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javassist-maven-plugin

A javassist maven plugin designed to alter class files after compilation. By creating your own ClassTransformer you can remove/add/edit code from/to/in your classes.

HelloWorldTransformer extends ClassTransformer

protected void applyTransformations(CtClass classToTransform) throws Exception

is where you do the actual work. Some operations are quite tricky in javassist.

To make this work create the following setup:

  • Project A, containing the classes you wish to process.

  • Project A-transformer, containing only the transformer class (you don't want this to end up in either A or A-android)

src/main/java/nl/topicus/hello/transformer/AndroidTransformer.java

<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>nl.topicus.hello</groupId>
	<artifactId>A-transformer</artifactId>
	<version>1.0-SNAPSHOT</version>
	<packaging>jar</packaging>

	<name>A Android Transformer</name>

	<dependencyManagement>
		<dependencies>
			<dependency>
				<groupId>nl.topicus.plugins</groupId>
				<artifactId>javassist-maven-plugin-core</artifactId>
				<version>2.1</version>
			</dependency>
		</dependencies>
	</dependencyManagement>

	<dependencies>
		<dependency>
			<groupId>nl.topicus.plugins</groupId>
			<artifactId>javassist-maven-plugin-core</artifactId>
		</dependency>
	</dependencies>

	<build>
		<plugins>
			<plugin>
				<groupId>org.apache.maven.plugins</groupId>
				<artifactId>maven-source-plugin</artifactId>
			</plugin>
		</plugins>
	</build>
</project>
  • Project A-android, containing nothing except a pom.xml (This can also be part of project A causing the compiled classfiles to be overridden)
<?xml version="1.0" encoding="UTF-8"?>
<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>nl.topicus.hello</groupId>
	<artifactId>A-android</artifactId>
	<version>1.0-SNAPSHOT</version>
	<packaging>jar</packaging>

	<dependencyManagement>
		<dependencies>
			<dependency>
				<groupId>nl.topicus.hello</groupId>
				<artifactId>A</artifactId>
				<version>${project.version}</version>
				<!-- set this to provided to make sure it won't be included in any android project -->
				<scope>provided</scope>
			</dependency>
		</dependencies>
	</dependencyManagement>

	<dependencies>
		<dependency>
			<groupId>nl.topicus.hello</groupId>
			<artifactId>A</artifactId>
		</dependency>
	</dependencies>

	<build>
		<pluginManagement>
			<plugins>
				<plugin>
					<groupId>nl.topicus.plugins</groupId>
					<artifactId>javassist-maven-plugin</artifactId>
					<version>2.1</version>
					<dependencies>
						<dependency>
							<groupId>nl.topicus.hello</groupId>
							<artifactId>A-transformer</artifactId>
							<version>1.0-SNAPSHOT</version>
						</dependency>
					</dependencies>
					<configuration>
<transformerClass>nl.topicus.hello.AndroidTransformer</transformerClass>
						<processInclusions>
							<inclusion>nl.topicus.hello</inclusion>
						</processInclusions>
						<processExclusions>
							<exclusion>nl.topicus.cobra.hello.exception</exclusion>
						</processExclusions>
						<exclusions>
							<exclusion>javax</exclusion>
						</exclusions>
					</configuration>
					<executions>
						<execution>
							<phase>process-classes</phase>
							<goals>
								<goal>javassist</goal>
							</goals>
						</execution>
					</executions>
				</plugin>
			</plugins>
		</pluginManagement>

		<plugins>
			<plugin>
				<groupId>nl.topicus.plugins</groupId>
				<artifactId>javassist-maven-plugin</artifactId>
			</plugin>
		</plugins>
	</build>
</project>

and this plugin will run the HelloWorldTransformer on all classes in (sub)package nl.topicus.hello but not nl.topicus.hello.country or nl.topicus.hello.universe. All 3 configuration lists are accessable in your ClassTransformer.

<project ...> ...

<dependencies>
	...
	<dependency>
		<groupId>nl.topicus.plugins</groupId>
		<artifactId>javassist-maven-plugin-core</artifactId>
		<version>1.0-SNAPSHOT</version>
		<scope>provided</scope>
	</dependency>
</dependencies>

<build>
	<plugins>
		...
		<plugin>
			<groupId>nl.topicus.plugins</groupId>
			<artifactId>javassist-maven-plugin</artifactId>
			<version>1.0-SNAPSHOT</version>
			<configuration>
				<transformerClass>com.example.HelloWorldTransformer</transformerClass>
				<processInclusions>
					<inclusion>nl.topicus.hello</<inclusion>
				</processInclusions>
				<processExclusions>
					<exclusion>nl.topicus.hello.country</<exclusion>
					<exclusion>nl.topicus.hello.universe</<exclusion>
				</processExclusions>
				<exclusions>
					<exclusion>nl.topicus.bye</<exclusion>
				</exclusions>
			</configuration>
			<executions>
				<execution>
					<phase>process-classes</phase>
					<goals>
						<goal>javassist</goal>
					</goals>
				</execution>
			</executions>
		</plugin>
	</plugins>
</build>