
[[using-boot]]
= Using Spring Boot

[partintro]
--
This section goes into more detail about how you should use Spring Boot. It covers topics
such as build systems, auto-configuration and how to run your applications. We also cover
some Spring Boot best practices. Although there is nothing particularly special about
Spring Boot (it is just another library that you can consume), there are a few
recommendations that, when followed, will make your development process just a
little easier.

If you're just starting out with Spring Boot, you should probably read the
_<<getting-started.adoc#getting-started, Getting Started>>_ guide before diving into
this section.
--



[[using-boot-build-systems]]
== Build systems
It is strongly recommended that you choose a build system that supports _dependency
management_, and one that can consume artifacts published to the "`Maven Central`"
repository. We would recommend that you choose Maven or Gradle. It is possible to get
Spring Boot to work with other build systems (Ant for example), but they will not be
particularly well supported.



[[using-boot-maven]]
=== Maven
Maven users can inherit from the `spring-boot-starter-parent` project to obtain sensible
defaults. The parent project provides the following features:

* Java 1.6 as the default compiler level.
* UTF-8 source encoding.
* A Dependency Management section, allowing you to omit `<version>` tags for common
  dependencies, inherited from the `spring-boot-dependencies` POM.
* Sensible https://maven.apache.org/plugins/maven-resources-plugin/examples/filter.html[resource filtering].
* Sensible plugin configuration (http://mojo.codehaus.org/exec-maven-plugin/[exec plugin],
  http://maven.apache.org/surefire/maven-surefire-plugin/[surefire],
  https://github.com/ktoso/maven-git-commit-id-plugin[Git commit ID],
  http://maven.apache.org/plugins/maven-shade-plugin/[shade]).
* Sensible resource filtering for `application.properties` and `application.yml`

On the last point: since the default config files accept
Spring style placeholders (`${...}`) the Maven filtering is changed to
use `@..@` placeholders (you can override that with a Maven property
`resource.delimiter`).



[[using-boot-maven-parent-pom]]
==== Inheriting the starter parent
To configure your project to inherit from the `spring-boot-starter-parent` simply set
the `parent`:

[source,xml,indent=0,subs="verbatim,quotes,attributes"]
----
	<!-- Inherit defaults from Spring Boot -->
	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>{spring-boot-version}</version>
	</parent>
----

NOTE: You should only need to specify the Spring Boot version number on this dependency.
If you import additional starters, you can safely omit the version number.



[[using-boot-maven-without-a-parent]]
==== Using Spring Boot without the parent POM
Not everyone likes inheriting from the `spring-boot-starter-parent` POM. You may have your
own corporate standard parent that you need to use, or you may just prefer to explicitly
declare all your Maven configuration.

If you don't want to use the `spring-boot-starter-parent`, you can still keep the benefit
of the dependency management (but not the plugin management) by using a `scope=import`
dependency:

[source,xml,indent=0,subs="verbatim,quotes,attributes"]
----
	<dependencyManagement>
 		<dependencies>
			<dependency>
				<!-- Import dependency management from Spring Boot -->
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-dependencies</artifactId>
				<version>{spring-boot-version}</version>
				<type>pom</type>
		        <scope>import</scope>
			</dependency>
		</dependencies>
	</dependencyManagement>
----



[[using-boot-maven-java-version]]
==== Changing the Java version
The `spring-boot-starter-parent` chooses fairly conservative Java compatibility. If you
want to follow our recommendation and use a later Java version you can add a
`java.version` property:

[source,xml,indent=0,subs="verbatim,quotes,attributes"]
----
	<properties>
		<java.version>1.8</java.version>
	</properties>
----



[[using-boot-maven-plugin]]
==== Using the Spring Boot Maven plugin
Spring Boot includes a <<build-tool-plugins.adoc#build-tool-plugins-maven-plugin, Maven plugin>>
that can package the project as an executable jar. Add the plugin to your `<plugins>`
section if you want to use it:

[source,xml,indent=0,subs="verbatim,quotes,attributes"]
----
	<build>
		<plugins>
			<plugin>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-maven-plugin</artifactId>
			</plugin>
		</plugins>
	</build>
----

NOTE: If you use the Spring Boot starter parent pom, you only need to add the plugin,
there is no need for to configure it unless you want to change the settings defined in
the parent.



[[using-boot-gradle]]
=== Gradle
Gradle users can directly import "`starter POMs`" in their `dependencies` section. Unlike
Maven, there is no "`super parent`" to import to share some configuration.

[source,groovy,indent=0,subs="attributes"]
----
	apply plugin: 'java'

	repositories {
ifeval::["{spring-boot-repo}" != "release"]
		maven { url "http://repo.spring.io/snapshot" }
		maven { url "http://repo.spring.io/milestone" }
endif::[]
ifeval::["{spring-boot-repo}" == "release"]
		jcenter()
endif::[]
	}

	dependencies {
		compile("org.springframework.boot:spring-boot-starter-web:{spring-boot-version}")
	}
----

The <<build-tool-plugins.adoc#build-tool-plugins-gradle-plugin,
`spring-boot-gradle-plugin`>> is also available and provides tasks to create executable
jars and run projects from source. It also provides
<<build-tool-plugins-gradle-dependency-management, dependency management>> that, among
other capabilities, allows you to omit the version number for any dependencies that are
managed by Spring Boot:

[source,groovy,indent=0,subs="attributes"]
----
	buildscript {
		repositories {
ifeval::["{spring-boot-repo}" != "release"]
			maven { url "http://repo.spring.io/snapshot" }
			maven { url "http://repo.spring.io/milestone" }
endif::[]
ifeval::["{spring-boot-repo}" == "release"]
			jcenter()
endif::[]
		}

		dependencies {
			classpath("org.springframework.boot:spring-boot-gradle-plugin:{spring-boot-version}")
		}
	}

	apply plugin: 'java'
	apply plugin: 'spring-boot'

	repositories {
ifeval::["{spring-boot-repo}" != "release"]
		maven { url "http://repo.spring.io/snapshot" }
		maven { url "http://repo.spring.io/milestone" }
endif::[]
ifeval::["{spring-boot-repo}" == "release"]
		jcenter()
endif::[]
	}

	dependencies {
		compile("org.springframework.boot:spring-boot-starter-web")
		testCompile("org.springframework.boot:spring-boot-starter-test")
	}
----



[[using-boot-ant]]
===  Ant
It is possible to build a Spring Boot project using Apache Ant+Ivy. The
`spring-boot-antlib` "`AntLib`" module is also available to help Ant create executable
jars.

To declare dependencies a typical `ivy.xml` file will look something like this:

[source,xml,indent=0]
----
	<ivy-module version="2.0">
		<info organisation="org.springframework.boot" module="spring-boot-sample-ant" />
		<configurations>
			<conf name="compile" description="everything needed to compile this module" />
			<conf name="runtime" extends="compile" description="everything needed to run this module" />
		</configurations>
		<dependencies>
			<dependency org="org.springframework.boot" name="spring-boot-starter"
				rev="${spring-boot.version}" conf="compile" />
		</dependencies>
	</ivy-module>
----

A typical `build.xml` will look like this:

[source,xml,indent=0]
----
	<project
		xmlns:ivy="antlib:org.apache.ivy.ant"
		xmlns:spring-boot="antlib:org.springframework.boot.ant"
		name="myapp" default="build">

		<property name="spring-boot.version" value="1.3.0.BUILD-SNAPSHOT" />

		<target name="resolve" description="--> retrieve dependencies with ivy">
			<ivy:retrieve pattern="lib/[conf]/[artifact]-[type]-[revision].[ext]" />
		</target>

		<target name="classpaths" depends="resolve">
			<path id="compile.classpath">
				<fileset dir="lib/compile" includes="*.jar" />
			</path>
		</target>

		<target name="init" depends="classpaths">
			<mkdir dir="build/classes" />
		</target>

		<target name="compile" depends="init" description="compile">
			<javac srcdir="src/main/java" destdir="build/classes" classpathref="compile.classpath" />
		</target>

		<target name="build" depends="compile">
			<spring-boot:exejar destfile="build/myapp.jar" classes="build/classes">
				<spring-boot:lib>
					<fileset dir="lib/runtime" />
				</spring-boot:lib>
			</spring-boot:exejar>
		</target>
	</project>
----

TIP: See the _<<howto.adoc#howto-build-an-executable-archive-with-ant>>_ "`How-to`" if
you don't want to use the `spring-boot-antlib` module.



[[using-boot-starter-poms]]
=== Starter POMs
Starter POMs are a set of convenient dependency descriptors that you can include in your
application. You get a one-stop-shop for all the Spring and related technology that you
need, without having to hunt through sample code and copy paste loads of dependency
descriptors. For example, if you want to get started using Spring and JPA for database
access, just include the `spring-boot-starter-data-jpa` dependency in your project, and
you are good to go.

The starters contain a lot of the dependencies that you need to get a project up and
running quickly and with a consistent, supported set of managed transitive dependencies.

.What's in a name
****
All **official** starters follow a similar naming pattern; `+spring-boot-starter-*+`,
where `+*+` is a particular type of application. This naming structure is intended to
help when you need to find a starter. The Maven integration in many IDEs allow you to
search dependencies by name. For example, with the appropriate Eclipse or STS plugin
installed, you can simply hit `ctrl-space` in the POM editor and type
"`spring-boot-starter`" for a complete list.

Third party starters should not start with `spring-boot-starter` as it is reserved for
official starters. A third-party starter for `acme` will be typically named
`acme-spring-boot-starter`.
****

The following application starters are provided by Spring Boot under the
`org.springframework.boot` group:

.Spring Boot application starters
|===
| Name | Description

|`spring-boot-starter`
|The core Spring Boot starter, including auto-configuration support, logging and YAML.

|`spring-boot-starter-actuator`
|Production ready features to help you monitor and manage your application.

|`spring-boot-starter-amqp`
|Support for the "`Advanced Message Queuing Protocol`" via `spring-rabbit`.

|`spring-boot-starter-aop`
|Support for aspect-oriented programming including `spring-aop` and AspectJ.

|`spring-boot-starter-artemis`
|Support for "`Java Message Service API`" via Apache Artemis.

|`spring-boot-starter-batch`
|Support for "`Spring Batch`" including HSQLDB database.

|`spring-boot-starter-cache`
|Support for Spring's Cache abstraction.

|`spring-boot-starter-cloud-connectors`
|Support for "`Spring Cloud Connectors`" which simplifies connecting to services in cloud
platforms like Cloud Foundry and Heroku.

|`spring-boot-starter-data-elasticsearch`
|Support for the Elasticsearch search and analytics engine including
`spring-data-elasticsearch`.

|`spring-boot-starter-data-gemfire`
|Support for the GemFire distributed data store including `spring-data-gemfire`.

|`spring-boot-starter-data-jpa`
|Support for the "`Java Persistence API`" including `spring-data-jpa`, `spring-orm`
and Hibernate.

|`spring-boot-starter-data-mongodb`
|Support for the MongoDB NoSQL Database, including `spring-data-mongodb`.

|`spring-boot-starter-data-rest`
|Support for exposing Spring Data repositories over REST via `spring-data-rest-webmvc`.

|`spring-boot-starter-data-solr`
|Support for the Apache Solr search platform, including `spring-data-solr`.

|`spring-boot-starter-freemarker`
|Support for the FreeMarker templating engine.

|`spring-boot-starter-groovy-templates`
|Support for the Groovy templating engine.

|`spring-boot-starter-hateoas`
|Support for HATEOAS-based RESTful services via `spring-hateoas`.

|`spring-boot-starter-hornetq`
|Support for "`Java Message Service API`" via HornetQ.

|`spring-boot-starter-integration`
|Support for common `spring-integration` modules.

|`spring-boot-starter-jdbc`
|Support for JDBC databases.

|`spring-boot-starter-jersey`
|Support for the Jersey RESTful Web Services framework.

|`spring-boot-starter-jta-atomikos`
|Support for JTA distributed transactions via Atomikos.

|`spring-boot-starter-jta-bitronix`
|Support for JTA distributed transactions via Bitronix.

|`spring-boot-starter-mail`
|Support for `javax.mail`.

|`spring-boot-starter-mobile`
|Support for `spring-mobile`.

|`spring-boot-starter-mustache`
|Support for the Mustache templating engine.

|`spring-boot-starter-redis`
|Support for the REDIS key-value data store, including `spring-redis`.

|`spring-boot-starter-security`
|Support for `spring-security`.

|`spring-boot-starter-social-facebook`
|Support for `spring-social-facebook`.

|`spring-boot-starter-social-linkedin`
|Support for `spring-social-linkedin`.

|`spring-boot-starter-social-twitter`
|Support for `spring-social-twitter`.

|`spring-boot-starter-test`
|Support for common test dependencies, including JUnit, Hamcrest and Mockito along with
 the `spring-test` module.

|`spring-boot-starter-thymeleaf`
|Support for the Thymeleaf templating engine, including integration with Spring.

|`spring-boot-starter-velocity`
|Support for the Velocity templating engine.

|`spring-boot-starter-web`
|Support for full-stack web development, including Tomcat and `spring-webmvc`.

|`spring-boot-starter-websocket`
|Support for WebSocket development.

|`spring-boot-starter-ws`
|Support for Spring Web Services.
|===

In addition to the application starters, the following starters can be used to
add _<<production-ready-features.adoc#production-ready, production ready>>_ features.

.Spring Boot production ready starters
|===
| Name | Description

|`spring-boot-starter-actuator`
|Adds production ready features such as metrics and monitoring.

|`spring-boot-starter-remote-shell`
|Adds remote `ssh` shell support.
|===

Finally, Spring Boot includes some starters that can be used if you want to exclude or
swap specific technical facets.

.Spring Boot technical starters
|===
| Name | Description

|`spring-boot-starter-jetty`
|Imports the Jetty HTTP engine (to be used as an alternative to Tomcat).

|`spring-boot-starter-log4j`
|Support the Log4J logging framework.

|`spring-boot-starter-logging`
|Import Spring Boot's default logging framework (Logback).

|`spring-boot-starter-tomcat`
|Import Spring Boot's default HTTP engine (Tomcat).

|`spring-boot-starter-undertow`
|Imports the Undertow HTTP engine (to be used as an alternative to Tomcat).
|===

TIP: For a list of additional community contributed starter POMs, see the
{github-master-code}/spring-boot-starters/README.adoc[README file] in the
`spring-boot-starters` module on GitHub.



[[using-boot-structuring-your-code]]
== Structuring your code
Spring Boot does not require any specific code layout to work, however, there are some
best practices that help.



[[using-boot-using-the-default-package]]
=== Using the "`default`" package
When a class doesn't include a `package` declaration it is considered to be in the
"`default package`". The use of the "`default package`" is generally discouraged, and
should be avoided. It can cause particular problems for Spring Boot applications that
use `@ComponentScan`, `@EntityScan` or `@SpringBootApplication` annotations, since every
class from every jar, will be read.

TIP: We recommend that you follow Java's recommended package naming conventions
and use a reversed domain name (for example, `com.example.project`).



[[using-boot-locating-the-main-class]]
=== Locating the main application class
We generally recommend that you locate your main application class in a root package
above other classes. The `@EnableAutoConfiguration` annotation is often placed on your
main class, and it implicitly defines a base "`search package`" for certain items. For
example, if you are writing a JPA application, the package of the
`@EnableAutoConfiguration` annotated class will be used to search for `@Entity` items.

Using a root package also allows the `@ComponentScan` annotation to be used without
needing to specify a `basePackage` attribute. You can also use the
`@SpringBootApplication` annotation if your main class is in the root package.

Here is a typical layout:

[indent=0]
----
	com
	 +- example
	     +- myproject
	         +- Application.java
	         |
	         +- domain
	         |   +- Customer.java
	         |   +- CustomerRepository.java
	         |
	         +- service
	         |   +- CustomerService.java
	         |
	         +- web
	             +- CustomerController.java
----

The `Application.java` file would declare the `main` method, along with the basic
`@Configuration`.

[source,java,indent=0]
----
	package com.example.myproject;

	import org.springframework.boot.SpringApplication;
	import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
	import org.springframework.context.annotation.ComponentScan;
	import org.springframework.context.annotation.Configuration;

	@Configuration
	@EnableAutoConfiguration
	@ComponentScan
	public class Application {

		public static void main(String[] args) {
			SpringApplication.run(Application.class, args);
		}

	}
----



[[using-boot-configuration-classes]]
== Configuration classes
Spring Boot favors Java-based configuration. Although it is possible to call
`SpringApplication.run()` with an XML source, we generally recommend that your primary
source is a `@Configuration` class. Usually the class that defines the `main` method
is also a good candidate as the primary `@Configuration`.

TIP: Many Spring configuration examples have been published on the Internet that use XML
configuration. Always try to use the equivalent Java-base configuration if possible.
Searching for `+enable*+` annotations can be a good starting point.



[[using-boot-importing-configuration]]
=== Importing additional configuration classes
You don't need to put all your `@Configuration` into a single class. The `@Import`
annotation can be used to import additional configuration classes. Alternatively, you
can use `@ComponentScan` to automatically pickup all Spring components, including
`@Configuration` classes.



[[using-boot-importing-xml-configuration]]
=== Importing XML configuration
If you absolutely must use XML based configuration, we recommend that you still start
with a `@Configuration` class. You can then use an additional `@ImportResource`
annotation to load XML configuration files.



[[using-boot-auto-configuration]]
== Auto-configuration
Spring Boot auto-configuration attempts to automatically configure your Spring
application based on the jar dependencies that you have added. For example, If
`HSQLDB` is on your classpath, and you have not manually configured any database
connection beans, then we will auto-configure an in-memory database.

You need to opt-in to auto-configuration by adding the `@EnableAutoConfiguration` or
`@SpringBootApplication` annotations to one of your `@Configuration` classes.

TIP: You should only ever add one `@EnableAutoConfiguration` annotation. We generally
recommend that you add it to your primary `@Configuration` class.



[[using-boot-replacing-auto-configuration]]
=== Gradually replacing auto-configuration
Auto-configuration is noninvasive,  at any point you can start to define your own
configuration to replace specific parts of the auto-configuration. For example, if
you add your own `DataSource` bean, the default embedded database support will back away.

If you need to find out what auto-configuration is currently being applied, and why,
starting your application with the `--debug` switch. This will log an auto-configuration
report to the console.



[[using-boot-disabling-specific-auto-configutation]]
=== Disabling specific auto-configuration
If you find that specific auto-configure classes are being applied that you don't want,
you can use the exclude attribute of `@EnableAutoConfiguration` to disable them.

[source,java,indent=0]
----
	import org.springframework.boot.autoconfigure.*;
	import org.springframework.boot.autoconfigure.jdbc.*;
	import org.springframework.context.annotation.*;

	@Configuration
	@EnableAutoConfiguration(exclude={DataSourceAutoConfiguration.class})
	public class MyConfiguration {
	}
----



[[using-boot-spring-beans-and-dependency-injection]]
== Spring Beans and dependency injection
You are free to use any of the standard Spring Framework techniques to define your beans
and their injected dependencies. For simplicity, we often find that using `@ComponentScan`
to find your beans, in combination with `@Autowired` constructor injection works well.

If you structure your code as suggested above (locating your application class in a root
package), you can add `@ComponentScan` without any arguments. All of your application
components (`@Component`, `@Service`, `@Repository`, `@Controller` etc.) will be
automatically registered as Spring Beans.

Here is an example `@Service` Bean that uses constructor injection to obtain a
required `RiskAssessor` bean.

[source,java,indent=0]
----
	package com.example.service;

	import org.springframework.beans.factory.annotation.Autowired;
	import org.springframework.stereotype.Service;

	@Service
	public class DatabaseAccountService implements AccountService {

		private final RiskAssessor riskAssessor;

		@Autowired
		public DatabaseAccountService(RiskAssessor riskAssessor) {
			this.riskAssessor = riskAssessor;
		}

		// ...

	}
----

TIP: Notice how using constructor injection allows the `riskAssessor` field to be marked
as `final`, indicating that it cannot be subsequently changed.



[[using-boot-using-springbootapplication-annotation]]
== Using the @SpringBootApplication annotation
Many Spring Boot developers always have their main class annotated with `@Configuration`,
`@EnableAutoConfiguration` and `@ComponentScan`. Since these annotations are so frequently
used together (especially if you follow the <<using-boot-structuring-your-code, best practices>>
above), Spring Boot provides a convenient `@SpringBootApplication` alternative.

The `@SpringBootApplication` annotation is equivalent to using `@Configuration`,
`@EnableAutoConfiguration` and `@ComponentScan` with their default attributes:


[source,java,indent=0]
----
	package com.example.myproject;

	import org.springframework.boot.SpringApplication;
	import org.springframework.boot.autoconfigure.SpringBootApplication;

	@SpringBootApplication // same as @Configuration @EnableAutoConfiguration @ComponentScan
	public class Application {

		public static void main(String[] args) {
			SpringApplication.run(Application.class, args);
		}

	}
----



[[using-boot-running-your-application]]
== Running your application
One of the biggest advantages of packaging your application as jar and using an embedded
HTTP server is that you can run your application as you would any other. Debugging Spring
Boot applications is also easy; you don't need any special IDE plugins or extensions.

NOTE: This section only covers jar based packaging, If you choose to package your
application as a war file you should refer to your server and IDE documentation.



[[using-boot-running-from-an-ide]]
=== Running from an IDE
You can run a Spring Boot application from your IDE as a simple Java application, however,
first you will need to import your project. Import steps will vary depending on your IDE
and build system. Most IDEs can import Maven projects directly, for example Eclipse users
can select `Import...` -> `Existing Maven Projects` from the `File` menu.

If you can't directly import your project into your IDE, you may be able to generate IDE
metadata using a build plugin. Maven includes plugins for
http://maven.apache.org/plugins/maven-eclipse-plugin/[Eclipse] and
http://maven.apache.org/plugins/maven-idea-plugin/[IDEA]; Gradle offers plugins
for http://www.gradle.org/docs/current/userguide/ide_support.html[various IDEs].

TIP: If you accidentally run a web application twice you will see a "`Port already in
use`" error. STS users can use the `Relaunch` button rather than `Run` to ensure that
any existing instance is closed.



[[using-boot-running-as-a-packaged-application]]
=== Running as a packaged application
If you use the Spring Boot Maven or Gradle plugins to create an executable jar you can
run your application using `java -jar`. For example:

[indent=0,subs="attributes"]
----
	$ java -jar target/myproject-0.0.1-SNAPSHOT.jar
----

It is also possible to run a packaged application with remote debugging support enabled.
This allows you to attach a debugger to your packaged application:

[indent=0,subs="attributes"]
----
	$ java -Xdebug -Xrunjdwp:server=y,transport=dt_socket,address=8000,suspend=n \
	       -jar target/myproject-0.0.1-SNAPSHOT.jar
----



[[using-boot-running-with-the-maven-plugin]]
=== Using the Maven plugin
The Spring Boot Maven plugin includes a `run` goal which can be used to quickly compile
and run your application. Applications run in an exploded form, and you can edit
resources for instant "`hot`" reload.

[indent=0,subs="attributes"]
----
	$ mvn spring-boot:run
----

You might also want to use the useful operating system environment variable:

[indent=0,subs="attributes"]
----
	$ export MAVEN_OPTS=-Xmx1024m -XX:MaxPermSize=128M -Djava.security.egd=file:/dev/./urandom
----

(The "`egd`" setting is to speed up Tomcat startup by giving it a faster source of
entropy for session keys.)



[[using-boot-running-with-the-gradle-plugin]]
=== Using the Gradle plugin
The Spring Boot Gradle plugin also includes a `bootRun` task which can be used to run
your application in an exploded form. The `bootRun` task is added whenever you import
the `spring-boot-plugin`

[indent=0,subs="attributes"]
----
	$ gradle bootRun
----

You might also want to use this useful operating system environment variable:

[indent=0,subs="attributes"]
----
	$ export JAVA_OPTS=-Xmx1024m -XX:MaxPermSize=128M -Djava.security.egd=file:/dev/./urandom
----



[[using-boot-hot-swapping]]
=== Hot swapping
Since Spring Boot applications are just plain Java applications, JVM hot-swapping should
work out of the box. JVM hot swapping is somewhat limited with the bytecode that it can
replace, for a more complete solution
http://zeroturnaround.com/software/jrebel/[JRebel] or the
https://github.com/spring-projects/spring-loaded[Spring Loaded] project can be used. The
`spring-boot-devtools` module also includes support for quick application restarts.

See the <<using-boot-devtools>> section below and the
<<howto.adoc#howto-hotswapping, Hot swapping "`How-to`">> for details.



[[using-boot-devtools]]
== Developer tools
Spring Boot includes an additional set of tools that can make the application
development experience a little more pleasant. The `spring-boot-devtools` module can be
included in any project to provide additional development-time features. To include
devtools support, simply add the module dependency to your build:

.Maven
[source,xml,indent=0,subs="verbatim,quotes,attributes"]
----
	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-devtools</artifactId>
		</dependency>
	</dependencies>
----

.Gradle
[source,groovy,indent=0,subs="attributes"]
----
	dependencies {
		compile("org.springframework.boot:spring-boot-devtools")
	}
----


NOTE: Developer tools are automatically disabled when running a fully packaged
application. If your application is launched using `java -jar` or if it's started using a
special classloader, then it is considered a "`production application`".



[[using-boot-devtools-property-defaults]]
=== Property defaults
Several of the libraries supported by Spring Boot use caches to improve performance. For
example, Thymeleaf will cache templates to save repeatedly parsing XML source files.
Whilst caching is very beneficial in production, it can be counter productive during
development. If you make a change to a template file in your IDE, you'll likely want to
immediately see the result.

Cache options are usually configured by settings in your `application.properties` file.
For example, Thymeleaf offers the `spring.thymeleaf.cache` property. Rather than needing
to set these properties manually, the `spring-boot-devtools` module will automatically
apply sensible development-time configuration.

TIP: For a complete list of the properties that are applied see
{sc-spring-boot-devtools}/autoconfigure/DevToolsPropertyDefaultsPostProcessor.{sc-ext}[DevToolsPropertyDefaultsPostProcessor].



[[using-boot-devtools-restart]]
=== Automatic restart
Applications that use `spring-boot-devtools` will automatically restart whenever files
on the classpath change. This can be a useful feature when working in an IDE as it gives
a very fast feedback loop for code changes. By default, any entry on the classpath that
points to a folder will be monitored for changes.

TIP: Automatic restart works very well when used with LiveReload.
<<using-boot-devtools-livereload,See below>> for details.

.Restart vs Reload
****
The restart technology provided by Spring Boot works by using two classloaders.
Classes that don't change (for example, those from third-party jars) are loaded into a
_base_ classloader. Classes that you're actively developing are loaded into a _restart_
classloader. When the application is restarted, the _restart_ classloader is thrown away
and a new one is created. This approach means that application restarts are typically much
faster than "`cold starts`" since the _base_ classloader is already available and
populated.

If you find that restarts aren't quick enough for your applications, you could consider
reloading technologies such as http://zeroturnaround.com/software/jrebel/[JRebel] from
ZeroTurnaround. These work by rewriting classes as they are loaded to make them more
amenable to reloading. https://github.com/spring-projects/spring-loaded[Spring Loaded]
provides another option, however it doesn't support as many frameworks and it isn't
commercially supported.
****



==== Excluding resources
Certain resources don't necessarily need to trigger a restart when they are changed. For
example, Thymeleaf templates can just be edited in-place. By default changing resources
in `/META-INF/maven`, `/META-INF/resources` ,`/resources` ,`/static` ,`/public` or
`/templates` will not trigger a restart. If you want to customize these exclusions you
can use the `spring.devtools.restart.exclude` property. For example, to exclude only
`/static` and `/public` you would set the following:

[indent=0]
----
	spring.devtools.restart.exclude=static/**,public/**
----



[[using-boot-devtools-restart-disable]]
==== Disabling restart
If you don't want to use the restart feature you can disable it using the
`spring.devtools.restart.enabled` property. In most cases you can set this in your
`application.properties` (this will still initialize the restart classloader but it won't
watch for file changes).

If you need to _completely_ disable restart support, for example, because it doesn't work
with a specific library, you need to set a `System` property before calling
`SpringApplication.run(...)`. For example:

[source,java,indent=0]
----
	public static void main(String[] args) {
		System.setProperty("spring.devtools.restart.enabled", "false");
		SpringApplication.run(MyApp.class, args);
	}
----



[[using-boot-devtools-restart-triggerfile]]
==== Using a trigger file
If you work with an IDE that continuously compiles changed files, you might prefer to
trigger restarts only at specific times. To do this you can use a "`trigger file`", which
is a special file that must be modified when you want to actually trigger a restart check.
The trigger file could be updated manually, or via an IDE plugin.

To use a trigger file use the `spring.devtools.restart.trigger-file` property.

TIP: You might want to set `spring.devtools.restart.trigger-file` as a
<<using-boot-devtools-globalsettings,global setting>> so that all your projects behave
in the same way.



[[using-boot-devtools-livereload]]
=== LiveReload
The `spring-boot-devtools` module includes an embedded LiveReload server that can be used
to trigger a browser refresh when a resource is changed. LiveReload browser extensions are
freely available for Chrome, Firefox and Safari from
http://livereload.com/extensions/[livereload.com].

If you don't want to start the LiveReload server when your application runs you can set
the `spring.devtools.livereload.enabled` property to `false`.

NOTE: You can only run one LiveReload server at a time, if you start multiple applications
from your IDE only the first will have livereload support.



[[using-boot-devtools-globalsettings]]
=== Global settings
You can configure global devtools settings by adding a file named
`.spring-boot-devtools.properties` to your `$HOME` folder (note that the filename starts
with "`.`"). Any properties added to this file will apply to _all_ Spring Boot
applications on your machine that use devtools. For example, to configure restart to
always use a <<using-boot-devtools-restart-triggerfile, trigger file>>, you would add
the following:

.~/.spring-boot-devtools.properties
[source,properties,indent=0]
----
	spring.devtools.reload.trigger-file=.reloadtrigger
----



[[using-boot-devtools-remote]]
=== Remote applications
The Spring Boot developer tools are not just limited to local development. You can also
use several features when running applications remotely. Remote support is opt-in, to
enable it you need to set a `spring.devtools.remote.secret` property. For example:

[source,properties,indent=0]
----
	spring.devtools.remote.secret=mysecret
----

WARNING: Enabling `spring-boot-devtools` on a remote application is a security risk. You
should never enable support on a production deployment.

Remote devtools support is provided in two parts; there is a server side endpoint that
accepts connections, and a client application that you run in your IDE. The server
component is automatically enabled when the `spring.devtools.remote.secret` property
is set. The client component must be launched manually.



==== Running the remote client application
The remote client application is designed to be run from within you IDE. You need to run
`org.springframework.boot.devtools.RemoteSpringApplication` using the same classpath as
the remote project that you're connecting to. The _non-option_ argument passed to the
application should be the remote URL that you are connecting to.

For example, if you are using Eclipse or STS, and you have a project named `my-app` that
you've deployed to Cloud Foundry, you would do the following:

* Select `Run Configurations...` from the `Run` menu.
* Create a new `Java Application` "`launch configuration`".
* Browse for the `my-app` project.
* Use `org.springframework.boot.devtools.RemoteSpringApplication` as the main class.
* Add `+++https://myapp.cfapps.io+++` to the `Program arguments` (or whatever your remote
  URL is).

A running remote client will look like this:

[indent=0,subs="attributes"]
----
	  .   ____          _                                              __ _ _
	 /\\ / ___'_ __ _ _(_)_ __  __ _          ___               _      \ \ \ \
	( ( )\___ | '_ | '_| | '_ \/ _` |        | _ \___ _ __  ___| |_ ___ \ \ \ \
	 \\/  ___)| |_)| | | | | || (_| []::::::[]   / -_) '  \/ _ \  _/ -_) ) ) ) )
	  '  |____| .__|_| |_|_| |_\__, |        |_|_\___|_|_|_\___/\__\___|/ / / /
	 =========|_|==============|___/===================================/_/_/_/
	 :: Spring Boot Remote :: {spring-boot-version}

	2015-06-10 18:25:06.632  INFO 14938 --- [           main] o.s.b.devtools.RemoteSpringApplication   : Starting RemoteSpringApplication on pwmbp with PID 14938 (/Users/pwebb/projects/spring-boot/code/spring-boot-devtools/target/classes started by pwebb in /Users/pwebb/projects/spring-boot/code/spring-boot-samples/spring-boot-sample-devtools)
	2015-06-10 18:25:06.671  INFO 14938 --- [           main] s.c.a.AnnotationConfigApplicationContext : Refreshing org.springframework.context.annotation.AnnotationConfigApplicationContext@2a17b7b6: startup date [Wed Jun 10 18:25:06 PDT 2015]; root of context hierarchy
	2015-06-10 18:25:07.043  WARN 14938 --- [           main] o.s.b.d.r.c.RemoteClientConfiguration    : The connection to http://localhost:8080 is insecure. You should use a URL starting with 'https://'.
	2015-06-10 18:25:07.074  INFO 14938 --- [           main] o.s.b.d.a.OptionalLiveReloadServer       : LiveReload server is running on port 35729
	2015-06-10 18:25:07.130  INFO 14938 --- [           main] o.s.b.devtools.RemoteSpringApplication   : Started RemoteSpringApplication in 0.74 seconds (JVM running for 1.105)
----

NOTE: Because the remote client is using the same classpath as the real application it
can directly read application properties. This is how the `spring.devtools.remote.secret`
property is read and passed to the server for authentication.

TIP: It's always advisable to use `https://` as the connection protocol so that traffic is
encrypted and passwords cannot be intercepted.



[[using-boot-devtools-remote-update]]
==== Remote update
The remote client will monitor your application classpath for changes in the same way as
the <<using-boot-devtools-restart,local restart>>. Any updated resource will be pushed
to the remote application and _(if required)_ trigger a restart. This can be quite helpful
if you are iterating on a feature that uses a cloud service that you don't have locally.
Generally remote updates and restarts are much quicker than a full rebuild and deploy
cycle.

NOTE: Files are only monitored when the remote client is running. If you change a file
before starting the remote client, it won't be pushed to the remote server.



[[using-boot-devtools-remote-debugtunnel]]
==== Remote debug tunnel
Java remote debugging is useful when diagnosing issues on a remote application.
Unfortunately, it's not always possible to enable remote debugging when your application
is deployed outside of your data center. Remote debugging can also be tricky to setup if
you are using a container based technology such as Docker.

To help work around these limitations, devtools supports tunneling of remote debug traffic
over HTTP. The remote client provides a local server on port `8000` that you can attach
a remote debugger to. Once a connection is established, debug traffic is sent over HTTP
to the remote application. You can use the `spring.devtools.remote.debug.local-port`
property if you want to use a different port.

You'll need to ensure that your remote application is started with remote debugging
enabled. Often this can be achieved by configuring `JAVA_OPTS`. For example, with
Cloud Foundry you can add the following to your `manifest.yml`:

[source,yaml,indent=0]
----
	---
	  env:
	    JAVA_OPTS: "-Xdebug -Xrunjdwp:server=y,transport=dt_socket,suspend=n"
----

TIP: Notice that you don't need to pass an `address=NNNN` option to `-Xrunjdwp`. If
omitted Java will simply pick a random free port.

NOTE: Debugging a remote service over the Internet can be slow and you might need to
increase timeouts in your IDE. For example, in Eclipse you can select `Java` -> `Debug`
from `Preferences...` and change the `Debugger timeout (ms)` to a more suitable value
(`60000` works well in most situations).



[[using-boot-packaging-for-production]]
== Packaging your application for production
Executable jars can be used for production deployment. As they are self-contained, they
are also ideally suited for cloud-based deployment.

For additional "`production ready`" features, such as health, auditing and metric REST
or JMX end-points; consider adding `spring-boot-actuator`. See
_<<production-ready-features.adoc#production-ready>>_ for details.



[[using-boot-whats-next]]
== What to read next
You should now have good understanding of how you can use Spring Boot along with some best
practices that you should follow. You can now go on to learn about specific
_<<spring-boot-features#boot-features, Spring Boot features>>_ in depth, or you
could skip ahead and read about the
"`<<production-ready-features#production-ready, production ready>>`" aspects of Spring
Boot.
