In this example we are going to see most of the capabilities from the maven compiler plugin.
Maven is a build automation tool used mainly for java projects from apache.
You can access to the maven compiler plugin here.
We are going to see some examples of the capabilities of the maven compiler plugin.
For this example we use the following technologies:
- MAC OSX
- Eclipse Mars.1
- Maven3
- JDK 1.8.0_65 64bits
- Maven compiler plugin 3.3
1. Introduction
The maven compiler plugin is called implicitely by the maven lifecycle in the appropiate phase so it is a special plugin. We don´t need to define it inside pom.xml it will be downloaded and executed when maven needs it.
Despite that, we can define it inside pom.xml in order to configure the way that maven should compile our classes.
The maven compiler plugin has two goals defined:
compile: Compile the classes undersrc/main/javatest-compile: Compile the classes undersrc/test/java
There is no need to define these goals inside pom.xml, as we said before, maven will invoke these goals when the maven lifecycle have to compile our classes.
Since maven 3 javax.tools.JavaCompiler (JDK 6 or newer) is used to compile java classes. The default source settings and also the default target settings is JDK 1.5 independently of the JDK you are using maven with.
We are going to see how we can change and control those things below.
2. Example project
For this example, we are going to use a java project with maven nature that will be packaged as a jar file. Eclipse Mars comes with maven support out of the box, so you don´t have to install anything. Our project will look like this
At this point, we have an empty maven project. We are going to define the maven compiler plugin inside plugin.xml in order to test the plugin capabilities.
The pom.xml will look like this
pom.xml:
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.javacodegeeks.examples</groupId>
<artifactId>maven-compiler-plugin-example</artifactId>
<version>1.0.0-SNAPSHOT</version>
<name>Maven compiler :: example</name>
<url>http://maven.apache.org</url>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>
<build>
<plugins>
<plugin>
<artifactId>maven-jar-plugin</artifactId>
<version>2.4</version>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.3</version>
</plugin>
</plugins>
</build>
</project>
3. Plugin options
We are going to see how we can do several things with the maven compiler plugin:
3.1. Set a different JDK to compile classes
We can set a different JDK in order to compile our classes, the following pom.xml shows how we can do it
pom.xml:
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.javacodegeeks.examples</groupId>
<artifactId>maven-compiler-plugin-example</artifactId>
<version>1.0.0-SNAPSHOT</version>
<name>Maven compiler :: example</name>
<url>http://maven.apache.org</url>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<JAVA_HOME_6>/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Home</JAVA_HOME_6>
</properties>
<build>
<plugins>
<plugin>
<artifactId>maven-jar-plugin</artifactId>
<version>2.4</version>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.3</version>
<configuration>
<executable>${JAVA_HOME_6}/bin/javac</executable>
<compilerVersion>1.6</compilerVersion>
</configuration>
</plugin>
</plugins>
</build>
</project>
You can set the JAVA_HOME_6 in maven settings.xml file or in another properties file in order to make your pom.xml more portable.
3.2. Specify a compatible JDK
If you want the compiled classes be compatible with a specific java version, you can set a specific JDK target and source, as you can see below
pom.xml:
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.javacodegeeks.examples</groupId>
<artifactId>maven-compiler-plugin-example</artifactId>
<version>1.0.0-SNAPSHOT</version>
<name>Maven compiler :: example</name>
<url>http://maven.apache.org</url>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<JAVA_HOME_6>/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Home</JAVA_HOME_6>
</properties>
<build>
<plugins>
<plugin>
<artifactId>maven-jar-plugin</artifactId>
<version>2.4</version>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.3</version>
<configuration>
<executable>${JAVA_HOME_6}/bin/javac</executable>
<compilerVersion>1.6</compilerVersion>
<source>1.4</source>
<target>1.4</target>
</configuration>
</plugin>
</plugins>
</build>
</project>
After compile your classes, it will be compatible with JDK 4.
3.3. Set some arguments to the compiler
You can pass arguments to the compiler, as you can see below
pom.xml:
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.javacodegeeks.examples</groupId>
<artifactId>maven-compiler-plugin-example</artifactId>
<version>1.0.0-SNAPSHOT</version>
<name>Maven compiler :: example</name>
<url>http://maven.apache.org</url>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<JAVA_HOME_6>/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Home</JAVA_HOME_6>
</properties>
<build>
<plugins>
<plugin>
<artifactId>maven-jar-plugin</artifactId>
<version>2.4</version>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.3</version>
<configuration>
<executable>${JAVA_HOME_6}/bin/javac</executable>
<compilerVersion>1.6</compilerVersion>
<source>1.4</source>
<target>1.4</target>
<fork>true</fork>
<meminitial>128m</meminitial>
<maxmem>512m</maxmem>
<verbose>true</verbose>
</configuration>
</plugin>
</plugins>
</build>
</project>
3.4. Set some specific arguments for the compiler that you have selected
If you have selected a specific compiler you can pass arguments to it with compilerArgs, as you can see below
pom.xml:
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.javacodegeeks.examples</groupId>
<artifactId>maven-compiler-plugin-example</artifactId>
<version>1.0.0-SNAPSHOT</version>
<name>Maven compiler :: example</name>
<url>http://maven.apache.org</url>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<JAVA_HOME_6>/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Home</JAVA_HOME_6>
</properties>
<build>
<plugins>
<plugin>
<artifactId>maven-jar-plugin</artifactId>
<version>2.4</version>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.3</version>
<configuration>
<executable>${JAVA_HOME_6}/bin/javac</executable>
<compilerVersion>1.6</compilerVersion>
<source>1.4</source>
<target>1.4</target>
<fork>true</fork>
<meminitial>128m</meminitial>
<maxmem>512m</maxmem>
<verbose>true</verbose>
<compilerArgs>
<arg>-verbose</arg>
<arg>-Xlint:all,-options,-path</arg>
</compilerArgs>
</configuration>
</plugin>
</plugins>
</build>
</project>
You can see all the arguments that you can pass to the maven compiler plugin here.
4. Conclusions
As we have saw the maven compiler plugin offers some interesting capabilities which we can take advantage of in order to make our code more portable and compatible.
5. Download the eclipse project
You can download the full source code of this example here: maven compiler plugin.zip
