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# 基于JavaAgent的全链路监控三《ByteBuddy操作监控方法字节码》

作者：小傅哥
博客：https://bugstack.cn (opens new window)

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# 案例简述

在第二章中我们已经可以监控方法执行耗时，虽然它能完成我们一些基本需要，但是为了增强代码的扩展性，我们需要使用字节码操作工具ByteBuddy来帮助我们实现更完善的监控程序。

Byte Buddy (opens new window) is a code generation and manipulation library for creating and modifying Java classes during the runtime of a Java application and without the help of a compiler. Other than the code generation utilities that ship with the Java Class Library (opens new window), Byte Buddy allows the creation of arbitrary classes and is not limited to implementing interfaces for the creation of runtime proxies. Furthermore, Byte Buddy offers a convenient API for changing classes either manually, using a Java agent or during a build.

# 环境准备

  1. IntelliJ IDEA Community Edition
  2. jdk1.8.0_45 64位

# 配置信息（路径相关修改为自己的）

  1. 配置位置：Run/Debug Configurations -> VM options
  2. 配置内容：-javaagent:E:\itstack\GIT\itstack.org\itstack-demo-agent\itstack-demo-agent-03\target\itstack-demo-agent-03-1.0.0-SNAPSHOT.jar=testargs

# 代码示例

itstack-demo-agent-03
├── pom.xml
└── src
    ├── main
    │   ├── java
    │   │   └── org.itstack.demo.agent
    │   │          ├── MethodCostTime.java
    │   │	         └── MyAgent.java
    │	 └── resources
    │         └── META-INF
    │                └── MANIFEST.MF 	
    └── test
         └── java
               └── org.itstack.demo.test
                     └── ApiTest.java
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pom.xml (引入ByteBuddy并打入到Agent包中)

<properties>
    <!-- Build args -->
	<argline>-Xms512m -Xmx512m</argline>
	<skip_maven_deploy>false</skip_maven_deploy>
	<updateReleaseInfo>true</updateReleaseInfo>
	<project.build.sourceEncoding>utf-8</project.build.sourceEncoding>
	<maven.test.skip>true</maven.test.skip>
	<!-- 自定义MANIFEST.MF -->
	<maven.configuration.manifestFile>src/main/resources/META-INF/MANIFEST.MF</maven.configuration.manifestFile>
</properties>

<dependencies>
	<dependency>
		<groupId>javassist</groupId>
		<artifactId>javassist</artifactId>
		<version>3.12.1.GA</version>
		<type>jar</type>
	</dependency>
	<dependency>
		<groupId>net.bytebuddy</groupId>
		<artifactId>byte-buddy</artifactId>
		<version>1.8.20</version>
	</dependency>
	<dependency>
		<groupId>net.bytebuddy</groupId>
		<artifactId>byte-buddy-agent</artifactId>
		<version>1.8.20</version>
	</dependency>
</dependencies>

<!-- 将javassist包打包到Agent中 -->
<plugin>
	<groupId>org.apache.maven.plugins</groupId>
	<artifactId>maven-shade-plugin</artifactId>
	<executions>
		<execution>
			<phase>package</phase>
			<goals>
				<goal>shade</goal>
			</goals>
		</execution>
	</executions>
	<configuration>
		<artifactSet>
			<includes>
				<include>javassist:javassist:jar:</include>
				<include>net.bytebuddy:byte-buddy:jar:</include>
                <include>net.bytebuddy:byte-buddy-agent:jar:</include>
			</includes>
		</artifactSet>
	</configuration>
</plugin>
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MethodCostTime.java

/**
 * 博客：http://itstack.org
 * 论坛：http://bugstack.cn
 * 公众号：bugstack虫洞栈  ｛获取学习源码｝
 * create by fuzhengwei on 2019
 */
public class MethodCostTime {

    @RuntimeType
    public static Object intercept(@Origin Method method, @SuperCall Callable<?> callable) throws Exception {
        long start = System.currentTimeMillis();
        try {
            // 原有函数执行
            return callable.call();
        } finally {
            System.out.println(method + " 方法耗时： " + (System.currentTimeMillis() - start) + "ms");
        }
    }

}
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MyAgent.java

/**
 * javaagent
 * 博客：http://itstack.org
 * 论坛：http://bugstack.cn
 * 公众号：bugstack虫洞栈  ｛获取学习源码｝
 * create by fuzhengwei on 2019
 */
public class MyAgent {

    //JVM 首先尝试在代理类上调用以下方法
    public static void premain(String agentArgs, Instrumentation inst) {
        System.out.println("this is my agent：" + agentArgs);
        
        AgentBuilder.Transformer transformer = (builder, typeDescription, classLoader, javaModule) -> {
            return builder
                    .method(ElementMatchers.any()) // 拦截任意方法
                    .intercept(MethodDelegation.to(MethodCostTime.class)); // 委托
        };

        AgentBuilder.Listener listener = new AgentBuilder.Listener() {
            @Override
            public void onDiscovery(String s, ClassLoader classLoader, JavaModule javaModule, boolean b) {

            }

            @Override
            public void onTransformation(TypeDescription typeDescription, ClassLoader classLoader, JavaModule javaModule, boolean b, DynamicType dynamicType) {

            }

            @Override
            public void onIgnored(TypeDescription typeDescription, ClassLoader classLoader, JavaModule javaModule, boolean b) {

            }

            @Override
            public void onError(String s, ClassLoader classLoader, JavaModule javaModule, boolean b, Throwable throwable) {

            }

            @Override
            public void onComplete(String s, ClassLoader classLoader, JavaModule javaModule, boolean b) {

            }

        };

        new AgentBuilder
                .Default()
                .type(ElementMatchers.nameStartsWith("org.itstack.demo.test")) // 指定需要拦截的类
                .transform(transformer)
                .with(listener)
                .installOn(inst);
    }


    //如果代理类没有实现上面的方法，那么 JVM 将尝试调用该方法
    public static void premain(String agentArgs) {
    }

}
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MANIFEST.MF

Manifest-Version: 1.0
Premain-Class: org.itstack.demo.agent.MyAgent
Can-Redefine-Classes: true
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ApiTest.java

/**
 * 博客：http://itstack.org
 * 论坛：http://bugstack.cn
 * 公众号：bugstack虫洞栈  ｛获取学习源码｝
 * create by fuzhengwei on 2019
 *
 * VM options：
 * -javaagent:E:\itstack\GIT\itstack.org\itstack-demo-agent\itstack-demo-agent-03\target\itstack-demo-agent-03-1.0.0-SNAPSHOT.jar=testargs
 */
public class ApiTest {

    public static void main(String[] args) throws InterruptedException {
        ApiTest apiTest = new ApiTest();
        apiTest.echoHi();
    }

    private void echoHi() throws InterruptedException {
        System.out.println("hi agent");
        Thread.sleep((long) (Math.random() * 500));
    }

}
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# 测试结果

this is my agent：testargs
hi agent
private void org.itstack.demo.test.ApiTest.echoHi() throws java.lang.InterruptedException 方法耗时： 329ms
public static void org.itstack.demo.test.ApiTest.main(java.lang.String[]) throws java.lang.InterruptedException 方法耗时： 329ms

Process finished with exit code 0
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