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Edit the core content reference documentation

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I edited for the usual stuff: spelling, punctuation,
grammar, formatting, usage, and voice.
This commit is contained in:
Jay Bryant
2018-08-24 16:18:42 -05:00
committed by Brian Clozel
parent d0ada5653f
commit 395e3d008c
9 changed files with 3549 additions and 2890 deletions
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@@ -1,6 +1,7 @@
[[beans]]
= The IoC container
= The IoC Container
This chapter covers Spring's Inversion of Control (IoC) container.
@@ -143,7 +144,7 @@ The following example shows the basic structure of XML-based configuration metad
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd">
<bean id="..." class="..."> <1> <2>
<bean id="..." class="..."> <1> <2>
<!-- collaborators and configuration for this bean go here -->
</bean>
@@ -2136,6 +2137,7 @@ modes:
[[beans-factory-autowiring-modes-tbl]]
.Autowiring modes
[cols="20%,80%"]
|===
| Mode| Explanation
@@ -2568,6 +2570,7 @@ The following table describes the supported scopes:
[[beans-factory-scopes-tbl]]
.Bean scopes
[cols="20%,80%"]
|===
| Scope| Description
@@ -2957,7 +2960,7 @@ understand the "`why`" as well as the "`how`" behind it:
<!-- an HTTP Session-scoped bean exposed as a proxy -->
<bean id="userPreferences" class="com.something.UserPreferences" scope="session">
<!-- instructs the container to proxy the surrounding bean -->
<aop:scoped-proxy/> <1>
<aop:scoped-proxy/> <1>
</bean>
<!-- a singleton-scoped bean injected with a proxy to the above bean -->
@@ -4565,7 +4568,7 @@ references and values even when you use the class outside of a container.
[[beans-autowired-annotation]]
=== @Autowired
=== Using `@Autowired`
NOTE: JSR 330's `@Inject` annotation can be used in place of Spring's `@Autowired` annotation
in the examples included in this section. See <<beans-standard-annotations,here>> for more details.
@@ -5007,13 +5010,13 @@ The following example shows corresponding bean definitions.
<context:annotation-config/>
<bean class="example.SimpleMovieCatalog">
<qualifier value="main"/> <1>
<qualifier value="main"/> <1>
<!-- inject any dependencies required by this bean -->
</bean>
<bean class="example.SimpleMovieCatalog">
<qualifier value="action"/> <2>
<qualifier value="action"/> <2>
<!-- inject any dependencies required by this bean -->
</bean>
@@ -5201,7 +5204,7 @@ following example:
public class MovieRecommender {
@Autowired
@Offline <1>
@Offline <1>
private MovieCatalog offlineCatalog;
// ...
@@ -5217,7 +5220,7 @@ Now the bean definition only needs a qualifier `type`, as shown in the following
[subs="verbatim,quotes"]
----
<bean class="example.SimpleMovieCatalog">
<qualifier type="Offline"/> <1>
<qualifier type="Offline"/> <1>
<!-- inject any dependencies required by this bean -->
</bean>
----
@@ -5459,7 +5462,7 @@ demonstrated in the following example:
private MovieFinder movieFinder;
@Resource(name="myMovieFinder") <1>
@Resource(name="myMovieFinder") <1>
public void setMovieFinder(MovieFinder movieFinder) {
this.movieFinder = movieFinder;
}
@@ -5516,7 +5519,7 @@ named customerPreferenceDao and then falls back to a primary type match for the
private CustomerPreferenceDao customerPreferenceDao;
@Resource
private ApplicationContext context; <1>
private ApplicationContext context; <1>
public MovieRecommender() {
}
@@ -5630,7 +5633,7 @@ annotation. For example, the `@Service` annotation mentioned <<beans-stereotype-
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component <1>
@Component <1>
public @interface Service {
// ....
@@ -8181,7 +8184,7 @@ the following example shows:
public class AppConfig {
@Bean("dataSource")
@Profile("development") <1>
@Profile("development") <1>
public DataSource standaloneDataSource() {
return new EmbeddedDatabaseBuilder()
.setType(EmbeddedDatabaseType.HSQL)
@@ -8191,7 +8194,7 @@ the following example shows:
}
@Bean("dataSource")
**@Profile("production")**
@Profile("production") <2>
public DataSource jndiDataSource() throws Exception {
Context ctx = new InitialContext();
return (DataSource) ctx.lookup("java:comp/env/jdbc/datasource");
@@ -8199,6 +8202,7 @@ the following example shows:
}
----
<1> The `standaloneDataSource` method is available only in the `development` profile.
<2> The `jndiDataSource` method is available only in the `production` profile.
====
[NOTE]
@@ -8895,6 +8899,7 @@ The following table describes the standard events that Spring provides:
[[beans-ctx-events-tbl]]
.Built-in Events
[cols="30%,70%"]
|===
| Event| Explanation
@@ -9460,6 +9465,7 @@ The following table lists features provided by the `BeanFactory` and
[[context-introduction-ctx-vs-beanfactory-feature-matrix]]
.Feature Matrix
[cols="50%,25%,25%"]
|===
| Feature | `BeanFactory` | `ApplicationContext`

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@@ -1,69 +1,64 @@
[[databuffers]]
= Data Buffers and Codecs
== Introduction
The `DataBuffer` interface defines an abstraction over byte buffers.
The main reason for introducing it, and not use the standard `java.nio.ByteBuffer` instead, is Netty.
Netty does not use `ByteBuffer`, but instead offers `ByteBuf` as an alternative.
The main reason for introducing it (and not using the standard `java.nio.ByteBuffer` instead) is Netty.
Netty does not use `ByteBuffer` but instead offers `ByteBuf` as an alternative.
Spring's `DataBuffer` is a simple abstraction over `ByteBuf` that can also be used on non-Netty
platforms (i.e. Servlet 3.1+).
platforms (that is, Servlet 3.1+).
== `DataBufferFactory`
The `DataBufferFactory` offers functionality to allocate new data buffers, as well as to wrap
The `DataBufferFactory` offers functionality to allocate new data buffers as well as to wrap
existing data.
The `allocate` methods allocate a new data buffer, with a default or given capacity.
Though `DataBuffer` implementation grow and shrink on demand, it is more efficient to give the
The `allocateBuffer` methods allocate a new data buffer with a default or given capacity.
Though `DataBuffer` implementations grow and shrink on demand, it is more efficient to give the
capacity upfront, if known.
The `wrap` methods decorate an existing `ByteBuffer` or byte array.
Wrapping does not involve allocation: it simply decorates the given data with a `DataBuffer`
Wrapping does not involve allocation. It decorates the given data with a `DataBuffer`
implementation.
There are two implementation of `DataBufferFactory`: the `NettyDataBufferFactory` which is meant
to be used on Netty platforms, such as Reactor Netty.
The other implementation, the `DefaultDataBufferFactory`, is used on other platforms, such as
Servlet 3.1+ servers.
There are two implementation of `DataBufferFactory`: the `NettyDataBufferFactory`
(for Netty platforms, such as Reactor Netty) and
`DefaultDataBufferFactory` (for other platforms, such as
Servlet 3.1+ servers).
== The `DataBuffer` Interface
== The `DataBuffer` interface
The `DataBuffer` interface is similar to `ByteBuffer`, but offers a number of advantages.
The `DataBuffer` interface is similar to `ByteBuffer` but offers a number of advantages.
Similar to Netty's `ByteBuf`, the `DataBuffer` abstraction offers independent read and write
positions.
This is different from the JDK's `ByteBuffer`, which only exposes one position for both reading and
writing, and a separate `flip()` operation to switch between the two I/O operations.
This is different from the JDK's `ByteBuffer`, which exposes only one position for both reading and
writing and a separate `flip()` operation to switch between the two I/O operations.
In general, the following invariant holds for the read position, write position, and the capacity:
====
[literal]
[subs="verbatim,quotes"]
--
0 <= read position <= write position <= capacity
--
====
When reading bytes from the `DataBuffer`, the read position is automatically updated in accordance with
the amount of data read from the buffer.
Similarly, when writing bytes to the `DataBuffer`, the write position is updated with the amount of
data written to the buffer.
Also, when writing data, the capacity of a `DataBuffer` is automatically expanded, just like `StringBuilder`,
Also, when writing data, the capacity of a `DataBuffer` is automatically expanded, in the same fashion as `StringBuilder`,
`ArrayList`, and similar types.
Besides the reading and writing functionality mentioned above, the `DataBuffer` also has methods to
view a (slice of a) buffer as `ByteBuffer`, `InputStream`, or `OutputStream`.
view a (slice of a) buffer as a `ByteBuffer`, an `InputStream`, or an `OutputStream`.
Additionally, it offers methods to determine the index of a given byte.
There are two implementation of `DataBuffer`: the `NettyDataBuffer` which is meant to be used on
Netty platforms, such as Reactor Netty.
The other implementation, the `DefaultDataBuffer`, is used on other platforms, such as Servlet 3.1+
servers.
As mentioned earlier, there are two implementation of `DataBufferFactory`: the `NettyDataBufferFactory`
(for Netty platforms, such as Reactor Netty) and
`DefaultDataBufferFactory` (for other platforms, such as
Servlet 3.1+ servers).
@@ -71,41 +66,42 @@ servers.
The `PooledDataBuffer` is an extension to `DataBuffer` that adds methods for reference counting.
The `retain` method increases the reference count by one.
The `release` method decreases the count by one, and releases the buffer's memory when the count
The `release` method decreases the count by one and releases the buffer's memory when the count
reaches 0.
Both of these methods are related to _reference counting_, a mechanism that is explained below.
Both of these methods are related to reference counting, a mechanism that we explain <<databuffer-reference-counting,later>>.
Note that `DataBufferUtils` offers useful utility methods for releasing and retaining pooled data
buffers.
These methods take a plain `DataBuffer` as parameter, but only call `retain` or `release` if the
These methods take a plain `DataBuffer` as a parameter but only call `retain` or `release` if the
passed data buffer is an instance of `PooledDataBuffer`.
[[databuffer-reference-counting]]
==== Reference Counting
Reference counting is not a common technique in Java; it is much more common in other programming
languages such as Object C and C++.
In and of itself, reference counting is not complex: it basically involves tracking the number of
Reference counting is not a common technique in Java. It is much more common in other programming
languages, such as Object C and C++.
In and of itself, reference counting is not complex. It basically involves tracking the number of
references that apply to an object.
The reference count of a `PooledDataBuffer` starts at 1, is incremented by calling `retain`,
and decremented by calling `release`.
As long as the buffer's reference count is larger than 0 the buffer will not be released.
When the number decreases to 0, the instance will be released.
In practice, this means that the reserved memory captured by the buffer will be returned back to
and is decremented by calling `release`.
As long as the buffer's reference count is larger than 0, the buffer is not released.
When the number decreases to 0, the instance is released.
In practice, this means that the reserved memory captured by the buffer is returned back to
the memory pool, ready to be used for future allocations.
In general, _the last component to access a `DataBuffer` is responsible for releasing it_.
In general, the last component to access a `DataBuffer` is responsible for releasing it.
Within Spring, there are two sorts of components that release buffers: decoders and transports.
Decoders are responsible for transforming a stream of buffers into other types (see <<codecs>> below),
and transports are responsible for sending buffers across a network boundary, typically as an HTTP message.
This means that if you allocate data buffers for the purpose of putting them into an outbound HTTP
message (i.e. client-side request or server-side response), they do not have to be released.
Decoders are responsible for transforming a stream of buffers into other types (see <<codecs>>),
and transports are responsible for sending buffers across a network boundary, typically as an HTTP message.
This means that, if you allocate data buffers for the purpose of putting them into an outbound HTTP
message (that is, a client-side request or server-side response), they do not have to be released.
The other consequence of this rule is that if you allocate data buffers that do not end up in the
body, for instance because of a thrown exception, you will have to release them yourself.
body (for instance, because of a thrown exception), you have to release them yourself.
The following snippet shows a typical `DataBuffer` usage scenario when dealing with methods that
throw exceptions:
====
[source,java,indent=0]
[subs="verbatim,quotes"]
----
@@ -130,46 +126,49 @@ throw exceptions:
<1> A new buffer is allocated.
<2> A boolean flag indicates whether the allocated buffer should be released.
<3> This example method loads data into the buffer. Note that the method can throw an `IOException`,
and therefore a `finally` block to release the buffer is required.
<4> If no exception occurred, we switch the `release` flag to `false` as the buffer will now be
<3> This example method loads data into the buffer. Note that the method can throw an `IOException`.
Therefore, a `finally` block to release the buffer is required.
<4> If no exception occurred, we switch the `release` flag to `false` as the buffer is now
released as part of sending the HTTP body across the wire.
<5> If an exception did occur, the flag is still set to `true`, and the buffer will be released
<5> If an exception did occur, the flag is still set to `true`, and the buffer is released
here.
====
=== DataBufferUtils
=== `DataBufferUtils`
`DataBufferUtils` contains various utility methods that operate on data buffers.
The `DataBufferUtils` class contains various utility methods that operate on data buffers.
It contains methods for reading a `Flux` of `DataBuffer` objects from an `InputStream` or NIO
`Channel`, and methods for writing a data buffer `Flux` to an `OutputStream` or `Channel`.
`Channel` and methods for writing a data buffer `Flux` to an `OutputStream` or `Channel`.
`DataBufferUtils` also exposes `retain` and `release` methods that operate on plain `DataBuffer`
instances (so that casting to a `PooledDataBuffer` is not required).
Additionally, `DataBufferUtils` exposes `compose`, which merges a stream of data buffers into one.
For instance, this method can be used to convert the entire HTTP body into a single buffer (and
from that, a `String`, or `InputStream`).
from that, a `String` or `InputStream`).
This is particularly useful when dealing with older, blocking APIs.
Note, however, that this puts the entire body in memory, and therefore uses more memory than a pure
streaming solution would.
[codecs]
[[codecs]]
== Codecs
The `org.springframework.core.codec` package contains the two main abstractions for converting a
stream of bytes into a stream of objects, or vice-versa.
stream of bytes into a stream of objects or vice-versa.
The `Encoder` is a strategy interface that encodes a stream of objects into an output stream of
data buffers.
The `Decoder` does the reverse: it turns a stream of data buffers into a stream of objects.
Note that a decoder instance needs to consider <<databuffer-reference-counting, reference counting>>.
The `Decoder` does the reverse: It turns a stream of data buffers into a stream of objects.
Note that a decoder instance needs to consider <<databuffer-reference-counting,reference counting>>.
Spring comes with a wide array of default codecs, capable of converting from/to `String`,
`ByteBuffer`, byte arrays, and also codecs that support marshalling libraries such as JAXB and
Spring comes with a wide array of default codecs (to convert from and to `String`,
`ByteBuffer`, and byte arrays) and codecs that support marshalling libraries such as JAXB and
Jackson (with https://github.com/FasterXML/jackson-core/issues/57[Jackson 2.9+ support for non-blocking parsing]).
Within the context of Spring WebFlux, codecs are used to convert the request body into a
`@RequestMapping` parameter, or to convert the return type into the response body that is sent back
`@RequestMapping` parameter or to convert the return type into the response body that is sent back
to the client.
The default codecs are configured in the `WebFluxConfigurationSupport` class, and can easily be
changed by overriding the `configureHttpMessageCodecs` when inheriting from that class.
For more information about using codecs in WebFlux, see <<web-reactive#webflux-codecs, this section>>.
The default codecs are configured in the `WebFluxConfigurationSupport` class. You can
change them by overriding the `configureHttpMessageCodecs` when you inherit from that class.
For more information about using codecs in WebFlux, see <<web-reactive#webflux-codecs>>.

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@@ -1,19 +1,19 @@
[[null-safety]]
= Null-safety
Although Java does not allow to express null-safety with its type system, Spring Framework
now provides following annotations in the `org.springframework.lang` package to declare
Although Java does not let you express null-safety with its type system, Spring Framework
now provides the following annotations in the `org.springframework.lang` package to let you declare
nullability of APIs and fields:
* {api-spring-framework}/lang/NonNull.html[`@NonNull`] annotation where specific parameter,
return value or field cannot be `null` (not needed on parameter and return value
where `@NonNullApi` and `@NonNullFields` apply) .
* {api-spring-framework}/lang/Nullable.html[`@Nullable`] annotation where specific
parameter, return value or field can be `null`.
* {api-spring-framework}/lang/NonNullApi.html[`@NonNullApi`] annotation at package level
declares non-null as the default behavior for parameters and return values.
* {api-spring-framework}/lang/NonNullFields.html[`@NonNullFields`] annotation at package
level declares non-null as the default behavior for fields.
* {api-spring-framework}/lang/NonNull.html[`@NonNull`]: Annotation to indicate that a specific parameter,
return value, or field cannot be `null` (not needed on parameter and return value
where `@NonNullApi` and `@NonNullFields` apply) .
* {api-spring-framework}/lang/Nullable.html[`@Nullable`]: Annotation to indicate that a specific
parameter, return value, or field can be `null`.
* {api-spring-framework}/lang/NonNullApi.html[`@NonNullApi`]: Annotation at the package level
that declares non-null as the default behavior for parameters and return values.
* {api-spring-framework}/lang/NonNullFields.html[`@NonNullFields`]: Annotation at the package
level that declares non-null as the default behavior for fields.
Spring Framework leverages itself these annotations, but they can also be used in any Spring based
Java project to declare null-safe APIs and optionally null-safe fields. Generic type arguments,
@@ -23,34 +23,30 @@ Nullability declaration are expected to be fine-tuned between Spring Framework r
including minor ones. Nullability of types used inside method bodies is outside of the
scope of this feature.
[NOTE]
====
Libraries like Reactor or Spring Data provide null-safe APIs leveraging this feature.
====
NOTE: Libraries like Reactor or Spring Data provide null-safe APIs that use this feature.
== Use cases
In addition to providing an explicit declaration for Spring Framework API nullability,
these annotation can be used by IDE (such as IDEA or Eclipse) to provide useful
warnings to Java developers related to null-safety in order to avoid `NullPointerException`
these annotations can be used by an IDE (such as IDEA or Eclipse) to provide useful
warnings related to null-safety in order to avoid `NullPointerException`
at runtime.
They are also used to make Spring API null-safe in Kotlin projects since Kotlin natively
They are also used to make Spring API null-safe in Kotlin projects, since Kotlin natively
supports https://kotlinlang.org/docs/reference/null-safety.html[null-safety]. More details
are available in <<languages#kotlin-null-safety,Kotlin support documentation>>.
are available in the <<languages#kotlin-null-safety,Kotlin support documentation>>.
== JSR 305 meta-annotations
Spring annotations are meta-annotated with https://jcp.org/en/jsr/detail?id=305[JSR 305]
annotations (a dormant but widely spread JSR). JSR 305 meta-annotations allows tooling vendors
like IDEA or Kotlin to provide null-safety support in a generic way, without having to hard-code
annotations (a dormant but widely spread JSR). JSR 305 meta-annotations let tooling vendors
like IDEA or Kotlin provide null-safety support in a generic way, without having to hard-code
support for Spring annotations.
It is not necessary nor recommended to add JSR 305 dependency in project classpath to
take advantage of Spring null-safe API. Only projects like
Spring-based libraries using null-safety annotations in their codebase should add
It is not necessary nor recommended to add JSR 305 dependency in the project classpath to
take advantage of Spring null-safe API. Only projects such as
Spring-based libraries that use null-safety annotations in their codebase should add
`com.google.code.findbugs:jsr305:3.0.2` with `compileOnly` Gradle configuration or Maven
`provided` scope to avoid compile warnings.

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@@ -1,16 +1,26 @@
[[resources]]
= Resources
This chapter covers how Spring handles resources and how you can work with resources in
Spring. It includes the following topics:
* <<resources-introduction>>
* <<resources-resource>>
* <<resources-implementations>>
* <<resources-resourceloader>>
* <<resources-resourceloaderaware>>
* <<resources-as-dependencies>>
* <<resources-app-ctx>>
[[resources-introduction]]
== Introduction
Java's standard `java.net.URL` class and standard handlers for various URL prefixes
unfortunately are not quite adequate enough for all access to low-level resources. For
Java's standard `java.net.URL` class and standard handlers for various URL prefixes,
unfortunately, are not quite adequate enough for all access to low-level resources. For
example, there is no standardized `URL` implementation that may be used to access a
resource that needs to be obtained from the classpath, or relative to a
resource that needs to be obtained from the classpath or relative to a
`ServletContext`. While it is possible to register new handlers for specialized `URL`
prefixes (similar to existing handlers for prefixes such as `http:`), this is generally
quite complicated, and the `URL` interface still lacks some desirable functionality,
@@ -18,13 +28,14 @@ such as a method to check for the existence of the resource being pointed to.
[[resources-resource]]
== The Resource interface
== The Resource Interface
Spring's `Resource` interface is meant to be a more capable interface for abstracting
access to low-level resources.
access to low-level resources. The following listing shows the `Resource` interface
definition:
====
[source,java,indent=0]
[subs="verbatim,quotes"]
----
@@ -46,7 +57,13 @@ access to low-level resources.
}
----
====
As the definition of the `Resource` interface shows, it extends the `InputStreamSource`
interface. The following listing shows the definition of the `InputStreamSource`
interface:
====
[source,java,indent=0]
[subs="verbatim,quotes"]
----
@@ -56,151 +73,158 @@ access to low-level resources.
}
----
====
Some of the most important methods from the `Resource` interface are:
* `getInputStream()`: locates and opens the resource, returning an `InputStream` for
* `getInputStream()`: Locates and opens the resource, returning an `InputStream` for
reading from the resource. It is expected that each invocation returns a fresh
`InputStream`. It is the responsibility of the caller to close the stream.
* `exists()`: returns a `boolean` indicating whether this resource actually exists in
* `exists()`: Returns a `boolean` indicating whether this resource actually exists in
physical form.
* `isOpen()`: returns a `boolean` indicating whether this resource represents a handle
with an open stream. If `true`, the `InputStream` cannot be read multiple times, and
must be read once only and then closed to avoid resource leaks. Will be `false` for
* `isOpen()`: Returns a `boolean` indicating whether this resource represents a handle
with an open stream. If `true`, the `InputStream` cannot be read multiple times and
must be read once only and then closed to avoid resource leaks. Returns `false` for
all usual resource implementations, with the exception of `InputStreamResource`.
* `getDescription()`: returns a description for this resource, to be used for error
* `getDescription()`: Returns a description for this resource, to be used for error
output when working with the resource. This is often the fully qualified file name or
the actual URL of the resource.
Other methods allow you to obtain an actual `URL` or `File` object representing the
resource (if the underlying implementation is compatible, and supports that
Other methods let you obtain an actual `URL` or `File` object representing the
resource (if the underlying implementation is compatible and supports that
functionality).
The `Resource` abstraction is used extensively in Spring itself, as an argument type in
Spring itself uses the `Resource` abstraction extensively, as an argument type in
many method signatures when a resource is needed. Other methods in some Spring APIs
(such as the constructors to various `ApplicationContext` implementations), take a
(such as the constructors to various `ApplicationContext` implementations) take a
`String` which in unadorned or simple form is used to create a `Resource` appropriate to
that context implementation, or via special prefixes on the `String` path, allow the
caller to specify that a specific `Resource` implementation must be created and used.
that context implementation or, via special prefixes on the `String` path, let the
caller specify that a specific `Resource` implementation must be created and used.
While the `Resource` interface is used a lot with Spring and by Spring, it's actually
While the `Resource` interface is used a lot with Spring and by Spring, it is actually
very useful to use as a general utility class by itself in your own code, for access to
resources, even when your code doesn't know or care about any other parts of Spring.
resources, even when your code does not know or care about any other parts of Spring.
While this couples your code to Spring, it really only couples it to this small set of
utility classes, which are serving as a more capable replacement for `URL`, and can be
utility classes, which serve as a more capable replacement for `URL` and can be
considered equivalent to any other library you would use for this purpose.
It is important to note that the `Resource` abstraction does not replace functionality:
it wraps it where possible. For example, a `UrlResource` wraps a URL, and uses the
NOTE: The `Resource` abstraction does not replace functionality.
It wraps it where possible. For example, a `UrlResource` wraps a URL and uses the
wrapped `URL` to do its work.
[[resources-implementations]]
== Built-in Resource implementations
== Built-in Resource Implementations
There are a number of `Resource` implementations that come supplied straight out of the
box in Spring:
Spring includes the following `Resource` implementations:
* <<resources-implementations-urlresource>>
* <<resources-implementations-classpathresource>>
* <<resources-implementations-filesystemresource>>
* <<resources-implementations-servletcontextresource>>
* <<resources-implementations-inputstreamresource>>
* <<resources-implementations-bytearrayresource>>
[[resources-implementations-urlresource]]
=== UrlResource
=== `UrlResource`
The `UrlResource` wraps a `java.net.URL`, and may be used to access any object that is
normally accessible via a URL, such as files, an HTTP target, an FTP target, etc. All
`UrlResource` wraps a `java.net.URL` and can be used to access any object that is
normally accessible with a URL, such as files, an HTTP target, an FTP target, and others. All
URLs have a standardized `String` representation, such that appropriate standardized
prefixes are used to indicate one URL type from another. This includes `file:` for
accessing filesystem paths, `http:` for accessing resources via the HTTP protocol,
`ftp:` for accessing resources via FTP, etc.
accessing filesystem paths, `http:` for accessing resources through the HTTP protocol,
`ftp:` for accessing resources through FTP, and others.
A `UrlResource` is created by Java code explicitly using the `UrlResource` constructor,
but will often be created implicitly when you call an API method which takes a `String`
argument which is meant to represent a path. For the latter case, a JavaBeans
`PropertyEditor` will ultimately decide which type of `Resource` to create. If the path
string contains a few well-known (to it, that is) prefixes such as `classpath:`, it will
create an appropriate specialized `Resource` for that prefix. However, if it doesn't
recognize the prefix, it will assume the this is just a standard URL string, and will
create a `UrlResource`.
A `UrlResource` is created by Java code by explicitly using the `UrlResource` constructor
but is often created implicitly when you call an API method that takes a `String`
argument meant to represent a path. For the latter case, a JavaBeans
`PropertyEditor` ultimately decides which type of `Resource` to create. If the path
string contains well-known (to it, that is) prefix (such as `classpath:`), it
creates an appropriate specialized `Resource` for that prefix. However, if it does not
recognize the prefix, it assume the string is a standard URL string and
creates a `UrlResource`.
[[resources-implementations-classpathresource]]
=== ClassPathResource
=== `ClassPathResource`
This class represents a resource which should be obtained from the classpath. This uses
This class represents a resource that should be obtained from the classpath. It uses
either the thread context class loader, a given class loader, or a given class for
loading resources.
This `Resource` implementation supports resolution as `java.io.File` if the class path
resource resides in the file system, but not for classpath resources which reside in a
jar and have not been expanded (by the servlet engine, or whatever the environment is)
to the filesystem. To address this the various `Resource` implementations always support
resource resides in the file system but not for classpath resources that reside in a
jar and have not been expanded (by the servlet engine or whatever the environment is)
to the filesystem. To address this, the various `Resource` implementations always support
resolution as a `java.net.URL`.
A `ClassPathResource` is created by Java code explicitly using the `ClassPathResource`
constructor, but will often be created implicitly when you call an API method which
takes a `String` argument which is meant to represent a path. For the latter case, a
JavaBeans `PropertyEditor` will recognize the special prefix `classpath:` on the string
path, and create a `ClassPathResource` in that case.
A `ClassPathResource` is created by Java code by explicitly using the `ClassPathResource`
constructor but is often created implicitly when you call an API method that
takes a `String` argument meant to represent a path. For the latter case, a
JavaBeans `PropertyEditor` recognizes the special prefix, `classpath:`, on the string
path and creates a `ClassPathResource` in that case.
[[resources-implementations-filesystemresource]]
=== FileSystemResource
=== `FileSystemResource`
This is a `Resource` implementation for `java.io.File` handles. It obviously supports
resolution as a `File`, and as a `URL`.
This is a `Resource` implementation for `java.io.File` handles. It supports
resolution as a `File` and as a `URL`.
[[resources-implementations-servletcontextresource]]
=== ServletContextResource
=== `ServletContextResource`
This is a `Resource` implementation for `ServletContext` resources, interpreting
This is a `Resource` implementation for `ServletContext` resources that interprets
relative paths within the relevant web application's root directory.
This always supports stream access and URL access, but only allows `java.io.File` access
It always supports stream access and URL access but allows `java.io.File` access only
when the web application archive is expanded and the resource is physically on the
filesystem. Whether or not it's expanded and on the filesystem like this, or accessed
directly from the JAR or somewhere else like a DB (it's conceivable) is actually
filesystem. Whether or not it is expanded and on the filesystem or accessed
directly from the JAR or somewhere else like a database (which is conceivable) is actually
dependent on the Servlet container.
[[resources-implementations-inputstreamresource]]
=== InputStreamResource
=== `InputStreamResource`
A `Resource` implementation for a given `InputStream`. This should only be used if no
An `InputStreamResource` is a `Resource` implementation for a given `InputStream`. It should be used only if no
specific `Resource` implementation is applicable. In particular, prefer
`ByteArrayResource` or any of the file-based `Resource` implementations where possible.
In contrast to other `Resource` implementations, this is a descriptor for an __already__
opened resource - therefore returning `true` from `isOpen()`. Do not use it if you need
to keep the resource descriptor somewhere, or if you need to read a stream multiple
In contrast to other `Resource` implementations, this is a descriptor for an already-opened
resource. Therefore, it returns `true` from `isOpen()`. Do not use it if you need
to keep the resource descriptor somewhere or if you need to read a stream multiple
times.
[[resources-implementations-bytearrayresource]]
=== ByteArrayResource
=== `ByteArrayResource`
This is a `Resource` implementation for a given byte array. It creates a
`ByteArrayInputStream` for the given byte array.
It's useful for loading content from any given byte array, without having to resort to a
It is useful for loading content from any given byte array without having to resort to a
single-use `InputStreamResource`.
[[resources-resourceloader]]
== The ResourceLoader
== The `ResourceLoader`
The `ResourceLoader` interface is meant to be implemented by objects that can return
(i.e. load) `Resource` instances.
(that is, load) `Resource` instances. The following listing shows the `ResourceLoader`
interface definition:
====
[source,java,indent=0]
[subs="verbatim,quotes"]
----
@@ -210,41 +234,49 @@ The `ResourceLoader` interface is meant to be implemented by objects that can re
}
----
====
All application contexts implement the `ResourceLoader` interface, and therefore all
All application contexts implement the `ResourceLoader` interface. Therefore, all
application contexts may be used to obtain `Resource` instances.
When you call `getResource()` on a specific application context, and the location path
specified doesn't have a specific prefix, you will get back a `Resource` type that is
specified doesn't have a specific prefix, you get back a `Resource` type that is
appropriate to that particular application context. For example, assume the following
snippet of code was executed against a `ClassPathXmlApplicationContext` instance:
====
[source,java,indent=0]
[subs="verbatim,quotes"]
----
Resource template = ctx.getResource("some/resource/path/myTemplate.txt");
----
====
What would be returned would be a `ClassPathResource`; if the same method was executed
against a `FileSystemXmlApplicationContext` instance, you'd get back a
`FileSystemResource`. For a `WebApplicationContext`, you'd get back a
`ServletContextResource`, and so on.
Against a `ClassPathXmlApplicationContext`, that code returns a `ClassPathResource`. If the same method were executed
against a `FileSystemXmlApplicationContext` instance, it would return a
`FileSystemResource`. For a `WebApplicationContext`, it would return a
`ServletContextResource`. It would similarly return appropriate objects for each context.
As such, you can load resources in a fashion appropriate to the particular application
As a result, you can load resources in a fashion appropriate to the particular application
context.
On the other hand, you may also force `ClassPathResource` to be used, regardless of the
application context type, by specifying the special `classpath:` prefix:
application context type, by specifying the special `classpath:` prefix, as the following
example shows:
====
[source,java,indent=0]
[subs="verbatim,quotes"]
----
Resource template = ctx.getResource("classpath:some/resource/path/myTemplate.txt");
----
====
Similarly, one can force a `UrlResource` to be used by specifying any of the standard
`java.net.URL` prefixes:
Similarly, you can force a `UrlResource` to be used by specifying any of the standard
`java.net.URL` prefixes. The following pair of examples use the `file` and `http`
prefixes:
====
[source,java,indent=0]
[subs="verbatim,quotes"]
----
@@ -256,8 +288,9 @@ Similarly, one can force a `UrlResource` to be used by specifying any of the sta
----
Resource template = ctx.getResource("http://myhost.com/resource/path/myTemplate.txt");
----
====
The following table summarizes the strategy for converting ``String``s to ``Resource``s:
The following table summarizes the strategy for converting `String` objects to `Resource` objects:
[[resources-resource-strings]]
.Resource strings
@@ -270,8 +303,7 @@ The following table summarizes the strategy for converting ``String``s to ``Reso
| file:
| `file:///data/config.xml`
| Loaded as a `URL`, from the filesystem. footnote:[But see also
pass:specialcharacters,macros[<<resources-filesystemresource-caveats>>].]
| Loaded as a `URL` from the filesystem. See also <<resources-filesystemresource-caveats>>.
| http:
| `http://myserver/logo.png`
@@ -284,13 +316,14 @@ The following table summarizes the strategy for converting ``String``s to ``Reso
[[resources-resourceloaderaware]]
== The ResourceLoaderAware interface
== The `ResourceLoaderAware` interface
The `ResourceLoaderAware` interface is a special marker interface, identifying objects
that expect to be provided with a `ResourceLoader` reference.
The `ResourceLoaderAware` interface is a special marker interface that identifies objects
that expect to be provided with a `ResourceLoader` reference. The following listing shows
the definition of the `ResourceLoaderAware` interface:
====
[source,java,indent=0]
[subs="verbatim,quotes"]
----
@@ -299,50 +332,51 @@ that expect to be provided with a `ResourceLoader` reference.
void setResourceLoader(ResourceLoader resourceLoader);
}
----
====
When a class implements `ResourceLoaderAware` and is deployed into an application
context (as a Spring-managed bean), it is recognized as `ResourceLoaderAware` by the
application context. The application context will then invoke the
application context. The application context then invokes
`setResourceLoader(ResourceLoader)`, supplying itself as the argument (remember, all
application contexts in Spring implement the `ResourceLoader` interface).
Of course, since an `ApplicationContext` is a `ResourceLoader`, the bean could also
Since an `ApplicationContext` is a `ResourceLoader`, the bean could also
implement the `ApplicationContextAware` interface and use the supplied application
context directly to load resources, but in general, it's better to use the specialized
`ResourceLoader` interface if that's all that's needed. The code would just be coupled
to the resource loading interface, which can be considered a utility interface, and not
context directly to load resources. However, in general, it is better to use the specialized
`ResourceLoader` interface if that is all you need. The code would be coupled only
to the resource loading interface (which can be considered a utility interface) and not to
the whole Spring `ApplicationContext` interface.
As of Spring 2.5, you can rely upon autowiring of the `ResourceLoader` as an alternative
to implementing the `ResourceLoaderAware` interface. The "traditional" `constructor` and
to implementing the `ResourceLoaderAware` interface. The "`traditional`" `constructor` and
`byType` autowiring modes (as described in <<beans-factory-autowire>>) are now capable
of providing a dependency of type `ResourceLoader` for either a constructor argument or
setter method parameter respectively. For more flexibility (including the ability to
autowire fields and multiple parameter methods), consider using the new annotation-based
autowiring features. In that case, the `ResourceLoader` will be autowired into a field,
constructor argument, or method parameter that is expecting the `ResourceLoader` type as
of providing a dependency of type `ResourceLoader` for either a constructor argument or a
setter method parameter, respectively. For more flexibility (including the ability to
autowire fields and multiple parameter methods), consider using the annotation-based
autowiring features. In that case, the `ResourceLoader` is autowired into a field,
constructor argument, or method parameter that expects the `ResourceLoader` type as
long as the field, constructor, or method in question carries the `@Autowired`
annotation. For more information, see <<beans-autowired-annotation>>.
[[resources-as-dependencies]]
== Resources as dependencies
== Resources as Dependencies
If the bean itself is going to determine and supply the resource path through some sort
of dynamic process, it probably makes sense for the bean to use the `ResourceLoader`
interface to load resources. Consider as an example the loading of a template of some
interface to load resources. For example, consider the loading of a template of some
sort, where the specific resource that is needed depends on the role of the user. If the
resources are static, it makes sense to eliminate the use of the `ResourceLoader`
interface completely, and just have the bean expose the `Resource` properties it needs,
and expect that they will be injected into it.
interface completely, have the bean expose the `Resource` properties it needs,
and expect them to be injected into it.
What makes it trivial to then inject these properties, is that all application contexts
register and use a special JavaBeans `PropertyEditor` which can convert `String` paths
to `Resource` objects. So if `myBean` has a template property of type `Resource`, it can
be configured with a simple string for that resource, as follows:
What makes it trivial to then inject these properties is that all application contexts
register and use a special JavaBeans `PropertyEditor`, which can convert `String` paths
to `Resource` objects. So, if `myBean` has a template property of type `Resource`, it can
be configured with a simple string for that resource, as the following example shows:
====
[source,xml,indent=0]
[subs="verbatim,quotes"]
----
@@ -350,16 +384,18 @@ be configured with a simple string for that resource, as follows:
<property name="template" value="some/resource/path/myTemplate.txt"/>
</bean>
----
====
Note that the resource path has no prefix, so because the application context itself is
going to be used as the `ResourceLoader`, the resource itself will be loaded via a
`ClassPathResource`, `FileSystemResource`, or `ServletContextResource` (as appropriate)
Note that the resource path has no prefix. Consequetly, because the application context itself is
going to be used as the `ResourceLoader`, the resource itself is loaded through a
`ClassPathResource`, a `FileSystemResource`, or a `ServletContextResource`,
depending on the exact type of the context.
If there is a need to force a specific `Resource` type to be used, then a prefix may be
used. The following two examples show how to force a `ClassPathResource` and a
`UrlResource` (the latter being used to access a filesystem file).
If you need to force a specific `Resource` type to be used, you can use a prefix.
The following two examples show how to force a `ClassPathResource` and a
`UrlResource` (the latter being used to access a filesystem file):
====
[source,xml,indent=0]
[subs="verbatim,quotes"]
----
@@ -371,49 +407,56 @@ used. The following two examples show how to force a `ClassPathResource` and a
----
<property name="template" value="file:///some/resource/path/myTemplate.txt"/>
----
====
[[resources-app-ctx]]
== Application contexts and Resource paths
== Application Contexts and Resource Paths
This section covers how to create application contexts with resources, including shortcuts
that work with XML, how to use wildcards, and other details.
[[resources-app-ctx-construction]]
=== Constructing application contexts
=== Constructing Application Contexts
An application context constructor (for a specific application context type) generally
takes a string or array of strings as the location path(s) of the resource(s) such as
takes a string or array of strings as the location paths of the resources, such as
XML files that make up the definition of the context.
When such a location path doesn't have a prefix, the specific `Resource` type built from
that path and used to load the bean definitions, depends on and is appropriate to the
specific application context. For example, if you create a
`ClassPathXmlApplicationContext` as follows:
When such a location path does not have a prefix, the specific `Resource` type built from
that path and used to load the bean definitions depends on and is appropriate to the
specific application context. For example, consider the following example, which creates a
`ClassPathXmlApplicationContext`:
====
[source,java,indent=0]
[subs="verbatim,quotes"]
----
ApplicationContext ctx = new ClassPathXmlApplicationContext("conf/appContext.xml");
----
====
The bean definitions will be loaded from the classpath, as a `ClassPathResource` will be
used. But if you create a `FileSystemXmlApplicationContext` as follows:
The bean definitions are loaded from the classpath, because a `ClassPathResource` is
used. However, consider the following example, which creates a `FileSystemXmlApplicationContext`:
====
[source,java,indent=0]
[subs="verbatim,quotes"]
----
ApplicationContext ctx =
new FileSystemXmlApplicationContext("conf/appContext.xml");
----
====
The bean definition will be loaded from a filesystem location, in this case relative to
the current working directory.
Now the bean definition is loaded from a filesystem location (in this case, relative to
the current working directory).
Note that the use of the special classpath prefix or a standard URL prefix on the
location path will override the default type of `Resource` created to load the
definition. So this `FileSystemXmlApplicationContext`...
location path overrides the default type of `Resource` created to load the
definition. Consider the folowing example:
[source,java,indent=0]
[subs="verbatim,quotes"]
@@ -422,23 +465,24 @@ definition. So this `FileSystemXmlApplicationContext`...
new FileSystemXmlApplicationContext("classpath:conf/appContext.xml");
----
... will actually load its bean definitions from the classpath. However, it is still a
Using `FileSystemXmlApplicationContext` loads the bean definitions from the classpath. However, it is still a
`FileSystemXmlApplicationContext`. If it is subsequently used as a `ResourceLoader`, any
unprefixed paths will still be treated as filesystem paths.
unprefixed paths are still treated as filesystem paths.
[[resources-app-ctx-classpathxml]]
==== Constructing ClassPathXmlApplicationContext instances - shortcuts
==== Constructing `ClassPathXmlApplicationContext` Instances -- Shortcuts
The `ClassPathXmlApplicationContext` exposes a number of constructors to enable
convenient instantiation. The basic idea is that one supplies merely a string array
containing just the filenames of the XML files themselves (without the leading path
information), and one __also__ supplies a `Class`; the `ClassPathXmlApplicationContext`
will derive the path information from the supplied class.
convenient instantiation. The basic idea is that you can supply merely a string array
that contains only the filenames of the XML files themselves (without the leading path
information) and also supplies a `Class`. The `ClassPathXmlApplicationContext`
then derives the path information from the supplied class.
An example will hopefully make this clear. Consider a directory layout that looks like
this:
Consider the following directory layout:
====
[literal]
[subs="verbatim,quotes"]
----
@@ -448,48 +492,53 @@ com/
daos.xml
MessengerService.class
----
====
A `ClassPathXmlApplicationContext` instance composed of the beans defined in the
`'services.xml'` and `'daos.xml'` could be instantiated like so...
The following example shows how a `ClassPathXmlApplicationContext` instance composed of the beans defined in
files named `services.xml` and `daos.xml` (which are on the classpath) can be instantiated:
====
[source,java,indent=0]
[subs="verbatim,quotes"]
----
ApplicationContext ctx = new ClassPathXmlApplicationContext(
new String[] {"services.xml", "daos.xml"}, MessengerService.class);
----
====
Please do consult the `ClassPathXmlApplicationContext` javadocs for details
See the {api-spring-framework}/jca/context/SpringContextResourceAdapter.html[`ClassPathXmlApplicationContext` Javadoc] for details
on the various constructors.
[[resources-app-ctx-wildcards-in-resource-paths]]
=== Wildcards in application context constructor resource paths
=== Wildcards in Application Context Constructor Resource Paths
The resource paths in application context constructor values may be a simple path (as
shown above) which has a one-to-one mapping to a target Resource, or alternately may
contain the special "classpath*:" prefix and/or internal Ant-style regular expressions
(matched using Spring's `PathMatcher` utility). Both of the latter are effectively
wildcards
The resource paths in application context constructor values may be simple paths (as
shown earlier), each of which has a one-to-one mapping to a target `Resource` or, alternately, may
contain the special "classpath*:" prefix or internal Ant-style regular expressions
(matched by using Spring's `PathMatcher` utility). Both of the latter are effectively
wildcards.
One use for this mechanism is when doing component-style application assembly. All
components can 'publish' context definition fragments to a well-known location path, and
when the final application context is created using the same path prefixed via
`classpath*:`, all component fragments will be picked up automatically.
One use for this mechanism is when you need to do component-style application assembly. All
components can 'publish' context definition fragments to a well-known location path, and,
when the final application context is created using the same path prefixed with
`classpath*:`, all component fragments are automatically picked up.
Note that this wildcarding is specific to use of resource paths in application context
constructors (or when using the `PathMatcher` utility class hierarchy directly), and is
Note that this wildcarding is specific to the use of resource paths in application context
constructors (or when you use the `PathMatcher` utility class hierarchy directly) and is
resolved at construction time. It has nothing to do with the `Resource` type itself.
It's not possible to use the `classpath*:` prefix to construct an actual `Resource`, as
You cannot use the `classpath*:` prefix to construct an actual `Resource`, as
a resource points to just one resource at a time.
[[resources-app-ctx-ant-patterns-in-paths]]
==== Ant-style Patterns
When the path location contains an Ant-style pattern, for example:
Path locations can contain Ant-style patterns, as the following example shows:
====
[literal]
[subs="verbatim"]
----
@@ -498,101 +547,103 @@ com/mycompany/**/applicationContext.xml
file:C:/some/path/*-context.xml
classpath:com/mycompany/**/applicationContext.xml
----
====
The resolver follows a more complex but defined procedure to try to resolve the
wildcard. It produces a Resource for the path up to the last non-wildcard segment and
When the path location contains an Ant-style pattern, the resolver follows a more complex procedure to try to resolve the
wildcard. It produces a `Resource` for the path up to the last non-wildcard segment and
obtains a URL from it. If this URL is not a `jar:` URL or container-specific variant
(e.g. `zip:` in WebLogic, `wsjar` in WebSphere, etc.), then a `java.io.File` is
(such as `zip:` in WebLogic, `wsjar` in WebSphere, and so on), a `java.io.File` is
obtained from it and used to resolve the wildcard by traversing the filesystem. In the
case of a jar URL, the resolver either gets a `java.net.JarURLConnection` from it or
manually parses the jar URL and then traverses the contents of the jar file to resolve
the wildcards.
[[resources-app-ctx-portability]]
===== Implications on portability
===== Implications on Portability
If the specified path is already a file URL (either explicitly, or implicitly because
the base `ResourceLoader` is a filesystem one), then wildcarding is guaranteed to work in
If the specified path is already a file URL (either implicitly because
the base `ResourceLoader` is a filesystem one or explicitly), wildcarding is guaranteed to work in
a completely portable fashion.
If the specified path is a classpath location, then the resolver must obtain the last
non-wildcard path segment URL via a `Classloader.getResource()` call. Since this is just
a node of the path (not the file at the end) it is actually undefined (in the
`ClassLoader` javadocs) exactly what sort of a URL is returned in this case. In
practice, it is always a `java.io.File` representing the directory, where the classpath
resource resolves to a filesystem location, or a jar URL of some sort, where the
classpath resource resolves to a jar location. Still, there is a portability concern on
If the specified path is a classpath location, the resolver must obtain the last
non-wildcard path segment URL by making a `Classloader.getResource()` call. Since this is just
a node of the path (not the file at the end), it is actually undefined (in the
`ClassLoader` Javadoc) exactly what sort of a URL is returned in this case. In
practice, it is always a `java.io.File` representing the directory (where the classpath
resource resolves to a filesystem location) or a jar URL of some sort w(here the
classpath resource resolves to a jar location). Still, there is a portability concern on
this operation.
If a jar URL is obtained for the last non-wildcard segment, the resolver must be able to
get a `java.net.JarURLConnection` from it, or manually parse the jar URL, to be able to
walk the contents of the jar, and resolve the wildcard. This will work in most
environments, but will fail in others, and it is strongly recommended that the wildcard
get a `java.net.JarURLConnection` from it or manually parse the jar URL, to be able to
walk the contents of the jar and resolve the wildcard. This does work in most
environments but fails in others, and we strongly recommend that the wildcard
resolution of resources coming from jars be thoroughly tested in your specific
environment before you rely on it.
[[resources-classpath-wildcards]]
==== The classpath*: prefix
==== The `classpath*:` Prefix
When constructing an XML-based application context, a location string may use the
special `classpath*:` prefix:
special `classpath*:` prefix, as the following example shows:
====
[source,java,indent=0]
[subs="verbatim,quotes"]
----
ApplicationContext ctx =
new ClassPathXmlApplicationContext("classpath*:conf/appContext.xml");
----
====
This special prefix specifies that all classpath resources that match the given name
must be obtained (internally, this essentially happens via a
`ClassLoader.getResources(...)` call), and then merged to form the final application
must be obtained (internally, this essentially happens through a call to
`ClassLoader.getResources(...)`) and then merged to form the final application
context definition.
[NOTE]
====
The wildcard classpath relies on the `getResources()` method of the underlying
NOTE: The wildcard classpath relies on the `getResources()` method of the underlying
classloader. As most application servers nowadays supply their own classloader
implementation, the behavior might differ especially when dealing with jar files. A
implementation, the behavior might differ, especially when dealing with jar files. A
simple test to check if `classpath*` works is to use the classloader to load a file from
within a jar on the classpath:
`getClass().getClassLoader().getResources("<someFileInsideTheJar>")`. Try this test with
files that have the same name but are placed inside two different locations. In case an
inappropriate result is returned, check the application server documentation for
settings that might affect the classloader behavior.
====
The `classpath*:` prefix can also be combined with a `PathMatcher` pattern in the
rest of the location path, for example `classpath*:META-INF/*-beans.xml`. In this
case, the resolution strategy is fairly simple: a `ClassLoader.getResources()` call is
You can also combine the `classpath*:` prefix with a `PathMatcher` pattern in the
rest of the location path (for example, `classpath*:META-INF/*-beans.xml`). In this
case, the resolution strategy is fairly simple: A `ClassLoader.getResources()` call is
used on the last non-wildcard path segment to get all the matching resources in the
class loader hierarchy, and then off each resource the same PathMatcher resolution
strategy described above is used for the wildcard subpath.
class loader hierarchy and then, off each resource, the same `PathMatcher` resolution
strategy described earlier is used for the wildcard subpath.
[[resources-wildcards-in-path-other-stuff]]
==== Other notes relating to wildcards
==== Other Notes Relating to Wildcards
Please note that `classpath*:` when combined with Ant-style patterns will only work
Note that `classpath*:`, when combined with Ant-style patterns, only works
reliably with at least one root directory before the pattern starts, unless the actual
target files reside in the file system. This means that a pattern like
target files reside in the file system. This means that a pattern such as
`classpath*:*.xml` might not retrieve files from the root of jar files but rather only
from the root of expanded directories.
Spring's ability to retrieve classpath entries originates from the JDK's
`ClassLoader.getResources()` method which only returns file system locations for a
passed-in empty string (indicating potential roots to search). Spring evaluates
`URLClassLoader` runtime configuration and the "java.class.path" manifest in jar files
as well but this is not guaranteed to lead to portable behavior.
`ClassLoader.getResources()` method, which only returns file system locations for an
empty string (indicating potential roots to search). Spring evaluates
`URLClassLoader` runtime configuration and the `java.class.path` manifest in jar files
as well, but this is not guaranteed to lead to portable behavior.
[NOTE]
====
The scanning of classpath packages requires the presence of corresponding directory
entries in the classpath. When you build JARs with Ant, make sure that you do __not__
entries in the classpath. When you build JARs with Ant, do not
activate the files-only switch of the JAR task. Also, classpath directories may not
get exposed based on security policies in some environments, e.g. standalone apps on
JDK 1.7.0_45 and higher (which requires 'Trusted-Library' setup in your manifests; see
get exposed based on security policies in some environments -- for example, stand-alone applications on
JDK 1.7.0_45 and higher (which requires 'Trusted-Library' to be set up in your manifests. See
http://stackoverflow.com/questions/19394570/java-jre-7u45-breaks-classloader-getresources).
On JDK 9's module path (Jigsaw), Spring's classpath scanning generally works as expected.
@@ -602,15 +653,17 @@ avoiding the aforementioned portability problems with searching the jar file roo
Ant-style patterns with `classpath:` resources are not guaranteed to find matching
resources if the root package to search is available in multiple class path locations.
This is because a resource such as
Consider the following example of a resource location:
====
[literal]
[subs="verbatim,quotes"]
----
com/mycompany/package1/service-context.xml
----
====
may be in only one location, but when a path such as
Now consider an Ant-style path that someone might use to try to find that file:
[literal]
[subs="verbatim,quotes"]
@@ -618,29 +671,31 @@ may be in only one location, but when a path such as
classpath:com/mycompany/**/service-context.xml
----
is used to try to resolve it, the resolver will work off the (first) URL returned by
`getResource("com/mycompany")`;. If this base package node exists in multiple
classloader locations, the actual end resource may not be underneath. Therefore,
preferably, use " `classpath*:`" with the same Ant-style pattern in such a case, which
will search all class path locations that contain the root package.
Such a resource may be in only one location, but when a path such as the preceding example
is used to try to resolve it, the resolver works off the (first) URL returned by
`getResource("com/mycompany");`. If this base package node exists in multiple
classloader locations, the actual end resource may not be there. Therefore, in such a case
you should prefer using `classpath*:` with the same Ant-style pattern, which
searches all class path locations that contain the root package.
[[resources-filesystemresource-caveats]]
=== FileSystemResource caveats
=== `FileSystemResource` Caveats
A `FileSystemResource` that is not attached to a `FileSystemApplicationContext` (that
is, a `FileSystemApplicationContext` is not the actual `ResourceLoader`) will treat
absolute vs. relative paths as you would expect. Relative paths are relative to the
is, when a `FileSystemApplicationContext` is not the actual `ResourceLoader`) treats
absolute and relative paths as you would expect. Relative paths are relative to the
current working directory, while absolute paths are relative to the root of the
filesystem.
For backwards compatibility (historical) reasons however, this changes when the
`FileSystemApplicationContext` is the `ResourceLoader`. The
`FileSystemApplicationContext` simply forces all attached `FileSystemResource` instances
`FileSystemApplicationContext` forces all attached `FileSystemResource` instances
to treat all location paths as relative, whether they start with a leading slash or not.
In practice, this means the following are equivalent:
In practice, this means the following examples are equivalent:
====
[source,java,indent=0]
[subs="verbatim,quotes"]
----
@@ -654,10 +709,12 @@ In practice, this means the following are equivalent:
ApplicationContext ctx =
new FileSystemXmlApplicationContext("/conf/context.xml");
----
====
As are the following: (Even though it would make sense for them to be different, as one
case is relative and the other absolute.)
The following exmaples are also equivalent (even though it would make sense for them to be different, as one
case is relative and the other absolute):
====
[source,java,indent=0]
[subs="verbatim,quotes"]
----
@@ -671,11 +728,14 @@ case is relative and the other absolute.)
FileSystemXmlApplicationContext ctx = ...;
ctx.getResource("/some/resource/path/myTemplate.txt");
----
====
In practice, if true absolute filesystem paths are needed, it is better to forgo the use
of absolute paths with `FileSystemResource` / `FileSystemXmlApplicationContext`, and
just force the use of a `UrlResource`, by using the `file:` URL prefix.
In practice, if you need true absolute filesystem paths, you should avoid using
absolute paths with `FileSystemResource` or `FileSystemXmlApplicationContext` and
force the use of a `UrlResource` by using the `file:` URL prefix. The following examples
show how to do so:
====
[source,java,indent=0]
[subs="verbatim,quotes"]
----
@@ -690,3 +750,4 @@ just force the use of a `UrlResource`, by using the `file:` URL prefix.
ApplicationContext ctx =
new FileSystemXmlApplicationContext("file:///conf/context.xml");
----
====

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