如何在类路径中放置javaagent的类

Question

我正在尝试开发一个javaagent,它可以在asm-4的帮助下编写代码.现在我遇到了一个非常基本的问题,javaagent的类加载器没有看到asm依赖,因此失败了.我是否必须提供一个jar-with-dependencies(又名maven build plugin),它包含代理所需的所有类,或者是否有另一种方法将类添加到java代理？直接在类路径中引用jar asm-all.jar没有帮助.构建jar-with-dependencies最初没有帮助,因为无法使用程序集插件设置Premain-Class属性.感谢帮助;-)

Answer 1

好的,通过实验找到它.依赖类应该是jar的一部分,可以通过maven程序集插件创建,例如:

    <plugin>
        <artifactId>maven-assembly-plugin</artifactId>
        <version>2.2</version>
        <configuration>
            <descriptorRefs>
                <descriptorRef>jar-with-dependencies</descriptorRef>
            </descriptorRefs>
            <archive>
                <index>true</index>
                <manifest>
                    <addDefaultImplementationEntries>true</addDefaultImplementationEntries>
                    <addDefaultSpecificationEntries>true</addDefaultSpecificationEntries>
                </manifest>
                <manifestEntries>
                    <Premain-Class>test.agent.MyAgent</Premain-Class>
                </manifestEntries>
            </archive>
        </configuration>
        <executions>
            <execution>
                <id>make-assembly</id>
                <!-- this is used for inheritance merges -->
                <phase>package</phase>
                <!-- append to the packaging phase. -->
                <goals>
                    <goal>single</goal>
                    <!-- goals == mojos -->
                </goals>
            </execution>
        </executions>
    </plugin>

使用jar作为javaagent路径,一切正常.

Answer 2

我关注了这篇博文.这是我如何使其工作,以获得对象的大小.

/MANIFEST.MF

Manifest-Version: 1.0
Premain-Class: ar.com.docdigital.InstrumentationApp
Can-Redefine-Classes: true
Can-Retransform-Classes: true
Can-Set-Native-Method-Prefix: true

在你的pom.xml中(注意我们引用自定义MANIFEST)

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-jar-plugin</artifactId>
    <configuration>
        <archive>
            <manifestFile>
                MANIFEST.MF
            </manifestFile>
            <manifest>
                <addClasspath>true</addClasspath>
                <mainClass>
                    ar.com.docdigital.App
                </mainClass>
            </manifest>
        </archive>
    </configuration>
</plugin>

我的仪器代理商:

package ar.com.docdigital;

import java.lang.instrument.Instrumentation;

/**
 *
 * @author juan.fernandez
 */
public class InstrumentationApp {
    private static Instrumentation instrumentation;

    public static void premain(String args, Instrumentation inst) {
        instrumentation = inst;
    }

    public static long getObjectSize(Object o) {
        return instrumentation.getObjectSize(o);
    }
}

我的主要应用:

包ar.com.docdigital;

import static ar.com.docdigital.InstrumentationApp.getObjectSize;

/**
 *
 * @author juan.fernandez
 */
public class App {
    public static void main (String[] args) {
        System.out.println("Size of CoprimeLong: " + getObjectSize(new CoprimesList.CoprimeLong(1L)));
        System.out.println("Size of Long: " + getObjectSize(new Long(1L)));

    }

}

全部放在一起和CLI输出:

$ mvn package
$ java -javaagent:target/primos-0.1.0-SNAPSHOT.jar -jar target/primos-0.1.0-SNAPSHOT.jar 
  Size of CoprimeLong: 24
  Size of Long: 24