为什么在Linux上使用Java Attach API失败? (即使Maven构建完成) [英] Why does using the Java Attach API fail on linux? (even though maven build completes)

问题描述

我一直在使用Java Attach API(tools.jar的一部分)将其附加到正在运行的Java进程，并从内部将其关闭.

它在Windows上完美运行.但是，当尝试在Linux上运行时实际执行附加代码时，我得到一个java.lang.NoClassDefFoundError，其中包含以下堆栈跟踪原因...

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)

我正在使用Maven，到目前为止，为了包含tools.jar，我有此部分.

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

值得注意的是，$ {java.home}评估为jre，但是即使我将其更改为jdk的直接路径，问题也相同.

我很沮丧...

解决方案

原来这是maven构建的问题.系统范围要求容器在启动时在类路径上传递tools.jar.一个简单的java -jar不能做到这一点(并且我不想添加一个显式的classpath参数).

我汇总来解决此问题的解决方案是让Maven构建使用配置文件选择位置，然后在打包阶段之前将jar预先安装在本地存储库中(允许依赖关系成为常规依赖关系). /p>

配置文件部分...

<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> 

安装文件部分...

<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>

依赖

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

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...

解决方案

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>

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