The Maven Toolchains provide a way for plugins to discover what JDK (or other tools) are to be used during the build, without the need to configure them. With toolchains, a project can now be built using a specific version of JDK independent from the one Maven is running with. (Think how JDK versions can be set in IDEs like Idea, NetBeans and Eclipse)
Toolchains would only work in Maven 2.0.9 and higher versions. For more details about it's design and implementation, please see Toolchains.
Below are the plugins which are toolchain-aware, meaning they can be used with toolchains:
There are two essential components that you need to configure in order to use toolchains. These are the maven-toolchains-plugin and the toolchains.xml file.
The maven-toolchains-plugin is the one that sets the toolchain to be used by the toolchain-aware plugins in your project. For example, you want to use a different JDK version to build your project. You can configure the version you want to use via this plugin as shown in the pom.xml below.
<plugins> ... <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-compiler-plugin</artifactId> <version>3.1</version> </plugin> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-toolchains-plugin</artifactId> <version>1.0</version> <executions> <execution> <phase>validate</phase> <goals> <goal>toolchain</goal> </goals> </execution> </executions> <configuration> <toolchains> <jdk> <version>1.5</version> <vendor>sun</vendor> </jdk> </toolchains> </configuration> </plugin> ... </plugins>
As you can see in the example above, a JDK toolchain with <version> "1.5" and <vendor> "sun" is to be used. Now how does the plugin know where this JDK is installed? This is where the toolchains.xml file comes in.
The toolchains.xml file (see below) is the configuration file where you set the installation paths of your toolchains. This file should be put in your $user.home/.m2 directory. When the maven-toolchains-plugin executes, the maven-toolchain component used by the plugin would look for the toolchains.xml file, read it and look for the matching toolchain configured in the plugin. In our example, that would be a JDK toolchain with <version> "1.5" and <vendor> "sun". Once a match is found, the plugin then sets the toolchain to be used in the MavenSession. As you can see in our toolchains.xml below, there is indeed a JDK toolchain with <version> "1.5" and <vendor> "sun" configured. So when the maven-compiler-plugin we've configured in our pom.xml above executes, it would see that a JDK toolchain is set in the MavenSession and would thereby use that toolchain (that would be the JDK installed at /path/to/jdk/1.5 for our example) to compile the sources.
<?xml version="1.0" encoding="UTF8"?> <toolchains> <toolchain> <type>jdk</type> <provides> <version>1.5</version> <vendor>sun</vendor> <id>default</id> </provides> <configuration> <jdkHome>/path/to/jdk/1.5</jdkHome> </configuration> </toolchain> <toolchain> <type>jdk</type> <provides> <version>1.6</version> <vendor>sun</vendor> <id>ide</id> </provides> <configuration> <jdkHome>/path/to/jdk/1.6</jdkHome> </configuration> </toolchain> <toolchain> <type>netbeans</type> <provides> <version>5.5</version> </provides> <configuration> <installDir>/path/to/netbeans/5.5</installDir> </configuration> </toolchain> </toolchains>
Note that you can configure as many toolchains as you want in your toolchains.xml file.