Why does using the Java Attach API fail on linux? (even though maven build completes)

问题

I've been using the Java Attach API (part of tools.jar) to attach to a running java process, and shut it down from within.

It works perfectly on Windows. However when trying to actually execute the attach code when running on linux I get a java.lang.NoClassDefFoundError with the following stack trace for the cause...

java.lang.ClassNotFoundException:com.sun.tools.attach.VirtualMachine...
    java.net.URLClassLoader$1.run(URLClassLoader.java:202)
    java.security.AccessController.doPrivileged(Native Method)
    java.net.URLClassLoader.findClass(URLClassLoader.java:190)
    java.lang.ClassLoader.loadClass(ClassLoader.java:306)
    sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
    java.lang.ClassLoader.loadClass(ClassLoader.java:247)

I'm using Maven and so far I have this section, in order to include tools.jar.

<dependency>
    <groupId>com.sun</groupId>
    <artifactId>tools</artifactId>
    <version>1.4.2</version>
    <scope>system</scope>
    <systemPath>${java.home}/../lib/tools.jar</systemPath>
</dependency>

Notably the ${java.home} evaluates to the jre but even if I change it to a direct path to the jdk, the issue is the same.

I'm pretty stumped...

回答1:

Turns out this was an issue with the maven build. The system scope requires the container to pass tools.jar on the classpath at launch. A simple java -jar does not do this (and I don't want to add an explicit classpath argument).

The solution I put together to solve this issue is to have the maven build choose the location using profiles, then pre-install the jar in the local repo before the package phase (allowing the dependancy to just be normal dependancy).

PROFILES SECTION...

<profiles>
    <profile>
        <id>default-profile</id>
        <activation>
            <activeByDefault>true</activeByDefault>
            <file>
                <exists>${java.home}/../lib/tools.jar</exists>
            </file>
        </activation>
        <properties>
            <toolsjar>${java.home}/../lib/tools.jar</toolsjar>
        </properties>
    </profile>
    <profile>
        <id>osx_profile</id>
        <activation>
            <activeByDefault>false</activeByDefault>
            <os>
                <family>mac</family>
            </os>
        </activation>
        <properties>
            <toolsjar>${java.home}/../Classes/classes.jar</toolsjar>
        </properties>
    </profile>
</profiles>

INSTALL-FILE SECTION...

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-install-plugin</artifactId>
    <executions>
        <execution>
            <id>jdk_tools</id>
            <phase>prepare-package</phase>
            <goals>
                <goal>install-file</goal>
            </goals>
            <configuration>
                <groupId>com.sun</groupId>
                <artifactId>tools</artifactId>
                <version>1.4.2</version>
                <packaging>jar</packaging>
                <file>${toolsjar}</file>
            </configuration>
        </execution>
    </executions>
</plugin>

DEPENDANCY

<dependency>
    <groupId>com.sun</groupId>
    <artifactId>tools</artifactId>
    <version>1.4.2</version>
</dependency>

来源：https://stackoverflow.com/questions/16379208/why-does-using-the-java-attach-api-fail-on-linux-even-though-maven-build-compl

标签

java

exception

maven

tools.jar