Java agent 探针

在 应用 main 之前执行， 可以做一些 字节码修改 类替换
很多应用监控组件就是这么干的

public static void premain(String agentArgs, Instrumentation inst)


META-INF/MANIFEST.MF 文件增加
Premain-Class: dyyx.agent.HelloAgent

需要在pom里增加




<build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-jar-plugin</artifactId>
                <version>2.3.1</version>
                <configuration>
                    <archive>
                        <manifestEntries>
                            <Premain-Class>dyyx.agent.HelloAgent</Premain-Class>
                        </manifestEntries>
                    </archive>
                </configuration>
            </plugin>
        </plugins>
    </build>
    




启动应用增加参数
-javaagent:/Users/dugang/fun/hellocode/project/helloagent/target/helloagent-1.0.0.jar=agentargs


java -javaagent:/Users/dugang/fun/hellocode/project/helloagent/target/helloagent-1.0.0.jar=agentargs  Hello


tomcat 测试

catalina.sh 里增加 jvm参数

-javaagent:/Users/dugang/soft/tomcat/agent9010/agent/helloagent-1.0.0.jar=agentargsForTomcat

JAVA_OPTS="$JAVA_OPTS -javaagent:/Users/dugang/soft/tomcat/agent9010/agent/helloagent-1.0.0.jar=agentargsForTomcat"


helloagent-1.0.0.jar 被所有应用共享


两个应用 共享  dyyx.agent.HelloAgent.map 

完整例子代码

https://gitee.com/dyyx/hellocode/tree/master/project/helloagent

应用读写 dyyx.agent.HelloAgent.map 的两个jsp代码

https://gitee.com/dyyx/hellocode/tree/master/project/helloagent/doc/webapp

 jvm外挂工具揭秘