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Document @Value support for Resource/Resource[] injection in ref docs

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See gh-26447
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Sam Brannen
2021-02-17 12:55:53 +01:00
parent ac58614be8
commit 87761397b0
1 changed files with 88 additions and 3 deletions
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91
src/docs/asciidoc/core/core-resources.adoc
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@@ -474,12 +474,37 @@ bean expose the `Resource` properties it needs, and expect them to be injected i
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:
to `Resource` objects. For example, the following `MyBean` class has a `template`
property of type `Resource`.
[source,java,indent=0,subs="verbatim,quotes",role="primary"]
.Java
----
package example;
public class MyBean {
private Resource template;
public setTemplate(Resource template) {
this.template = template;
}
// ...
}
----
[source,kotlin,indent=0,subs="verbatim,quotes",role="secondary"]
.Kotlin
----
class MyBean(var template: Resource)
----
In an XML configuration file, the `template` property can be configured with a simple
string for that resource, as the following example shows:
[source,xml,indent=0,subs="verbatim,quotes"]
----
<bean id="myBean" class="...">
<bean id="myBean" class="example.MyBean">
<property name="template" value="some/resource/path/myTemplate.txt"/>
</bean>
----
@@ -503,6 +528,66 @@ latter being used to access a file in the filesystem):
<property name="template" value="file:///some/resource/path/myTemplate.txt"/>
----
If the `MyBean` class is refactored for use with annotation-driven configuration, the
path to `myTemplate.txt` can be stored under a key named `template.path` -- for example,
in a properties file made available to the Spring `Environment` (see
<<beans-environment>>). The template path can then be referenced via the `@Value`
annotation using a property placeholder (see <<beans-value-annotations>>). Spring will
retrieve the value of the template path as a string, and a special `PropertyEditor` will
convert the string to a `Resource` object to be injected into the `MyBean` constructor.
The following example demonstrates how to achieve this.
[source,java,indent=0,subs="verbatim,quotes",role="primary"]
.Java
----
@Component
public class MyBean {
private final Resource template;
public MyBean(@Value("${template.path}") Resource template) {
this.template = template;
}
// ...
}
----
[source,kotlin,indent=0,subs="verbatim,quotes",role="secondary"]
.Kotlin
----
@Component
class MyBean(@Value("\${template.path}") private val template: Resource)
----
If we want to support multiple templates discovered under the same path in multiple
locations in the classpath -- for example, in multiple jars in the classpath -- we can
use the special `classpath*:` prefix and wildcarding to define a `templates.path` key as
`classpath*:/config/templates/*.txt`. If we redefine the `MyBean` class as follows,
Spring will convert the template path pattern into an array of `Resource` objects that
can be injected into the `MyBean` constructor.
[source,java,indent=0,subs="verbatim,quotes",role="primary"]
.Java
----
@Component
public class MyBean {
private final Resource[] templates;
public MyBean(@Value("${templates.path}") Resource[] templates) {
this.templates = templates;
}
// ...
}
----
[source,kotlin,indent=0,subs="verbatim,quotes",role="secondary"]
.Kotlin
----
@Component
class MyBean(@Value("\${templates.path}") private val templates: Resource[])
----