项目总结：java agent的使用

测试团队会做java agent的事，实现测试模拟，各种数据采集等等工作，而这些不需要开发改代码来做到，只需要挂载下agent。

javaagent认识和例子代码

例子：

java -javaagent:/Users/mubi/git_workspace/common1/common-test/target/common-test-1.0-SNAPSHOT-jar-with-dependencies.jar com.test.AgentTest

不改变代码，而是在java命令后加入-javaagent:xx.jar实现对class的干预

java.lang.instrument

https://docs.oracle.com/javase/8/docs/api/java/lang/instrument/package-summary.html

Provides services that allow Java programming language agents to instrument programs running on the JVM.

即在Java编程语言中，允许Java代理（Agents）进行代码插装（Instrumentation）的服务主要由Java Agent API提供。这个API允许开发者在运行时动态修改或增强Java应用程序的字节码，而无需修改源代码或重新编译。这对于性能监控、调试、安全增强等场景非常有用。

自定义实现一个javaagent

• MyAgent

package com.test;import java.lang.instrument.Instrumentation;/*** @Author mubi* @Date 2025/2/11 21:45*/
public class MyAgent {/*** jvm 参数形式启动，运行此方法** @param agentArgs agentArgs 是我们启动 Java Agent 时带进来的参数，比如-javaagent:xxx.jar agentArgs* @param inst*/public static void premain(String agentArgs, Instrumentation inst) {System.out.println("premain");customLogic(inst);}/*** 动态 attach 方式启动，运行此方法** @param agentArgs* @param inst*/public static void agentmain(String agentArgs, Instrumentation inst) {System.out.println("agentmain");customLogic(inst);}/*** 打印所有已加载的类名称 修改字节码** @param inst*/private static void customLogic(Instrumentation inst) {inst.addTransformer(new MyTransformer(), true);}
}

• 使用javaassist改变class文件

package com.test;import java.io.ByteArrayInputStream;
import java.lang.instrument.ClassFileTransformer;
import java.lang.instrument.IllegalClassFormatException;
import java.security.ProtectionDomain;
import javassist.ClassPool;
import javassist.CtClass;
import javassist.CtMethod;/*** javassist 官方文档：http://www.javassist.org/tutorial/tutorial.html*/
public class MyTransformer implements ClassFileTransformer {@Overridepublic byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined,ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException {
//        System.out.println("正在加载类：" + className);if (!"com/test/Hello".equals(className)) {return classfileBuffer;}CtClass cl = null;try {ClassPool classPool = ClassPool.getDefault();cl = classPool.makeClass(new ByteArrayInputStream(classfileBuffer));CtMethod ctMethod = cl.getDeclaredMethod("test");System.out.println("获取方法名称：" + ctMethod.getName());// 声明本地变量ctMethod.addLocalVariable("start", CtClass.longType);ctMethod.addLocalVariable("end", CtClass.longType);ctMethod.insertBefore("System.out.println(\" 动态插入的打印语句 \");");ctMethod.insertBefore("start = System.currentTimeMillis();");// $_在Javassist中是一个特殊的变量，代表当前正在处理的类或方法中的表达式ctMethod.insertAfter("System.out.println($_);");ctMethod.insertAfter("end = System.currentTimeMillis();");// 输出耗时ctMethod.insertAfter("System.out.println((end-start) + \" ms\");");byte[] transformed = cl.toBytecode();return transformed;} catch (Exception e) {e.printStackTrace();}return classfileBuffer;}
}

• 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"><parent><artifactId>common1</artifactId><groupId>com.container</groupId><version>1.0-SNAPSHOT</version></parent><modelVersion>4.0.0</modelVersion><artifactId>common-test</artifactId><repositories></repositories><build><plugins><plugin><artifactId>maven-compiler-plugin</artifactId><configuration><source>1.8</source><target>1.8</target></configuration></plugin><plugin><groupId>org.apache.maven.plugins</groupId><artifactId>maven-assembly-plugin</artifactId><version>2.5.5</version><executions><execution><goals><goal>attached</goal></goals><id>make-assembly</id><phase>package</phase><configuration><descriptorRefs><descriptorRef>jar-with-dependencies</descriptorRef></descriptorRefs><archive><manifestEntries><Premain-Class>com.test.MyAgent</Premain-Class><Agent-Class>com.test.MyAgent</Agent-Class><Can-Redefine-Classes>true</Can-Redefine-Classes><Can-Retransform-Classes>true</Can-Retransform-Classes></manifestEntries></archive></configuration></execution></executions></plugin></plugins></build><properties><spring.verson>5.1.3.RELEASE</spring.verson></properties><dependencies><dependency><groupId>org.javassist</groupId><artifactId>javassist</artifactId><version>3.27.0-GA</version></dependency><dependency><groupId>org.ow2.asm</groupId><artifactId>asm</artifactId><version>9.2</version></dependency><dependency><groupId>org.ow2.asm</groupId><artifactId>asm-commons</artifactId><version>9.2</version></dependency><dependency><groupId>cglib</groupId><artifactId>cglib</artifactId><version>3.3.0</version></dependency><dependency><groupId>junit</groupId><artifactId>junit</artifactId><version>4.12</version></dependency></dependencies></project>

即加入：

<plugin><groupId>org.apache.maven.plugins</groupId><artifactId>maven-assembly-plugin</artifactId><version>2.5.5</version><executions><execution><goals><goal>attached</goal></goals><id>make-assembly</id><phase>package</phase><configuration><descriptorRefs><descriptorRef>jar-with-dependencies</descriptorRef></descriptorRefs><archive><manifestEntries><Premain-Class>com.test.MyAgent</Premain-Class><Agent-Class>com.test.MyAgent</Agent-Class><Can-Redefine-Classes>true</Can-Redefine-Classes><Can-Retransform-Classes>true</Can-Retransform-Classes></manifestEntries></archive></configuration></execution></executions></plugin>

按照要求：

An agent JAR file may have both the Premain-Class and Agent-Class attributes present in the manifest. When the agent is started on the command-line using the -javaagent option then the Premain-Class attribute specifies the name of the agent class and the Agent-Class attribute is ignored. Similarly, if the agent is started sometime after the VM has started, then the Agent-Class attribute specifies the name of the agent class (the value of Premain-Class attribute is ignored).

一个代理 JAR 文件可能在清单中同时具有 Premain-Class 和 Agent-Class 属性。 当使用 -javaagent 选项在命令行上启动代理时，Premain-Class 属性指定代理类的名称，而 Agent-Class 属性将被忽略。 同样，如果代理在 VM 启动后的某个时间启动，则 Agent-Class 属性指定代理类的名称（忽略 Premain-Class 属性的值）

打包生成agent jar

agent jar测试

定义Hello类

package com.test;import java.util.concurrent.TimeUnit;/*** @Author mubi* @Date 2025/2/11 23:20*/
public class Hello {public String test() {try {TimeUnit.SECONDS.sleep(1);System.out.println("hello logic");} catch (Exception e) {}return "hello test";}
}

测试类并加上agent参数-javaagent:/Users/mubi/git_workspace/common1/common-test/target/common-test-1.0-SNAPSHOT-jar-with-dependencies.jar

测试输出如下：

即完成了代理行为。

回顾javaagent的作用

JVM启动后，JVM会执行指定Agent类的premain()方法，在premain()中可以调用Instrumentation对象的addTransformer方法注册ClassFileTransformer。当JVM加载类时会将类文件的字节数组传递给ClassFileTransformer的transform方法，在transform方法中对Class文件进行解析和修改，之后JVM就会加载转换后的Class文件。

这样实例化后执行代理了的方法就能完成，因为class文件被改过且加载好了。

项目中用到agent的例子

当一个入口流程开始后，可能因为不同的输入，执行了不同的链路。业务如果有扩展，那么就需要是否有执行，以及执行情况。

如下 AppProcess的entry方法 的入参不同，调用的扩展点实现也是不同，通过java agent 可以采集到信息

• 主程序

package com.pro.biz;import java.util.ArrayList;
import java.util.List;public class AppProcess {/*** 扩展点*/List<StrService> strServiceList;public AppProcess() {strServiceList = new ArrayList<>();}public void setStrServiceList(){strServiceList.add(new X());strServiceList.add(new Y());}public void entry(String name) {String s = null;if (name.equals("one")) {s = strServiceList.get(0).dealStr(name);System.out.println("entry:" + s);return;}if (name.equals("all")) {for (StrService strService : strServiceList) {s = strService.dealStr(name);System.out.println("entry:" + s);}return;}}
}

• 扩展点和实现类
  

• Agent类

package com.pro.agent;import java.lang.instrument.Instrumentation;/*** @Author mubi* @Date 2025/2/12 22:54*/
public class StatAgent {/*** jvm 参数形式启动，运行此方法** @param agentArgs agentArgs 是我们启动 Java Agent 时带进来的参数，比如-javaagent:xxx.jar agentArgs* @param inst*/public static void premain(String agentArgs, Instrumentation inst) {
//        System.out.println("premain");customLogic(inst);}/*** 动态 attach 方式启动，运行此方法** @param agentArgs* @param inst*/public static void agentmain(String agentArgs, Instrumentation inst) {
//        System.out.println("agentmain");customLogic(inst);}/*** 打印所有已加载的类名称 修改字节码** @param inst*/private static void customLogic(Instrumentation inst) {inst.addTransformer(new StatTransformer(), true);}
}

package com.pro.agent;import javassist.ClassPool;
import javassist.CtClass;
import javassist.CtMethod;import java.io.ByteArrayInputStream;
import java.lang.instrument.ClassFileTransformer;
import java.lang.instrument.IllegalClassFormatException;
import java.security.ProtectionDomain;/*** @Author mubi* @Date 2025/2/12 22:55*/
public class StatTransformer implements ClassFileTransformer {@Overridepublic byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException {
//        if (!"com/pro/biz/AppProcess".equals(className)) {
//            return classfileBuffer;
//        }CtClass cl = null;try {ClassPool classPool = ClassPool.getDefault();cl = classPool.makeClass(new ByteArrayInputStream(classfileBuffer));CtMethod ctMethod = null;try{ctMethod = cl.getDeclaredMethod("dealStr");}catch (Exception e){}if(ctMethod != null && !className.equals("com/pro/biz/StrService")) {
//                System.out.println("获取到方法名称：" + ctMethod.getName());
//                System.out.println(className);//                ctMethod.insertBefore("System.out.println(\"入参: \" + $1);");
//                ctMethod.insertAfter("System.out.println(\"出参: \" + $_);");ctMethod.insertAfter("com.pro.stat.StrServiceCallStats.addCallInfo($0.getClass().getName(), $1, $_);");//                StringBuilder methodBody = new StringBuilder();
//                methodBody.append("{")
//                        .append("System.out.println(\"Input: \" + $1);") // input parameter
//                        .append("$r = $proceed($$);") // proceed with the original method
                        .append("System.out.println(\"Output: \" + result);") // output
//                        .append("return $r;")
//                        .append("}");
//
//                // Modify the method
//                ctMethod.setBody(methodBody.toString());}// 插入统计代码
//            String insertBeforeCode = "{ $_ = $proceed($$); " +
//                    "StrServiceCallStats.addCallInfo($0.strServiceList.get($index).getClass().getName(), $1, $_); }";
//            entryMethod.insertBefore(insertBeforeCode);byte[] transformed = cl.toBytecode();return transformed;} catch (Exception e) {e.printStackTrace();}return classfileBuffer;}
}

• 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"><parent><artifactId>common1</artifactId><groupId>com.container</groupId><version>1.0-SNAPSHOT</version></parent><modelVersion>4.0.0</modelVersion><artifactId>common-project</artifactId><build><plugins><plugin><artifactId>maven-compiler-plugin</artifactId><configuration><source>1.8</source><target>1.8</target></configuration></plugin><plugin><groupId>org.apache.maven.plugins</groupId><artifactId>maven-assembly-plugin</artifactId><version>2.5.5</version><executions><execution><goals><goal>attached</goal></goals><id>make-assembly</id><phase>package</phase><configuration><descriptorRefs><descriptorRef>jar-with-dependencies</descriptorRef></descriptorRefs><archive><manifestEntries><Premain-Class>com.pro.agent.StatAgent</Premain-Class><Agent-Class>com.pro.agent.StatAgent</Agent-Class><Can-Redefine-Classes>true</Can-Redefine-Classes><Can-Retransform-Classes>true</Can-Retransform-Classes></manifestEntries></archive></configuration></execution></executions></plugin></plugins></build><properties><spring.verson>5.1.3.RELEASE</spring.verson></properties><dependencies><dependency><groupId>org.javassist</groupId><artifactId>javassist</artifactId><version>3.29.0-GA</version></dependency><dependency><groupId>org.ow2.asm</groupId><artifactId>asm</artifactId><version>9.2</version></dependency><dependency><groupId>org.ow2.asm</groupId><artifactId>asm-commons</artifactId><version>9.2</version></dependency><dependency><groupId>cglib</groupId><artifactId>cglib</artifactId><version>3.3.0</version></dependency><dependency><groupId>junit</groupId><artifactId>junit</artifactId><version>4.12</version></dependency></dependencies></project>

打包后生成agent jar， 运行时加上-javaagent:/Users/mubi/git_workspace/common1/common-project/target/common-project-1.0-SNAPSHOT-jar-with-dependencies.jar