如何将tools.jar包含到uberjar中（使用maven-shade-plugin）？

Question

pom.xml:

<?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/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>test</groupId>
    <artifactId>test</artifactId>
    <version>1.0-SNAPSHOT</version>

    <dependencies>
        <dependency>
            <groupId>com.sun</groupId>
            <artifactId>tools</artifactId>
            <version>1.7</version>
            <scope>system</scope>
            <systemPath>${java.home}/../lib/tools.jar</systemPath>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-shade-plugin</artifactId>
                <version>2.3</version>
                <executions>
                    <execution>
                        <phase>package</phase>
                        <goals>
                            <goal>shade</goal>
                        </goals>
                        <configuration>
                            <transformers>
                                <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
                                    <mainClass>test.Test</mainClass>
                                </transformer>
                            </transformers>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>

</project>

mvn install completes successfully, (ie maven sees tools.jar dependency during the build), but on execution I have

Exception in thread "main" java.lang.NoClassDefFoundError: com/sun/tools/javac/api/JavacScope
    at test.Test.main(Test.java:24)
Caused by: java.lang.ClassNotFoundException: com.sun.tools.javac.api.JavacScope
...

Answer 1

maven-shade plugin assumes System dependencies be present and it doesn't actually include them inside fat-jar

fast dirty workaround is to install tools.jar into your maven repository and refer it as a compile scoped dependency

better workaround is to use maven-assembly-plugin and include tools.jar as a <file>

Answer 2

Most <scope>system</scope> dependencies are not made available to plugins.

Also, including the tools.jar in your uberjar isn't terribly portable across newer versions of JVMs. Its fine if you have a super controlled and limited deployment environment, but generally its better to discover the tools.jar and use it.

Here's an example from the maven-javadoc-plugin itself (it looks up the tools.jar and then validates that the active classloader has classes from the tools.jar)

In your case, instead of looking for com.sun.tools.doclets.Taglet , you'd look for com.sun.tools.javac.api.JavacScope to verify a valid environment.

From there it would be trivial to build up a new ClassLoader with your uberjar + tools.jar and then execute what you need from a valid Thread.currentThread().setContextClassLoader() scope