背景描述
javaagent是在JDK5之后提供的新特性，也可以叫java代理。开发者通过这种机制(Instrumentation)可以在加载class文件之前修改方法的字节码(此时字节码尚未加入JVM)，动态更改类方法实现AOP，提供监控服务如；方法调用时长、可用率、内存等。
开发简述
通过实现ClassFileTransformer接口方法，动态更改方法的字节码。在方法前后加上时间戳，最后执行完成输出执行时长。
环境准备
1、IntelliJ IDEA Community Edition 2018.3.1 x64
2、jdk1.8 64位
配置信息（路径相关修改为自己的）
1、java调试时配置
2.1、配置位置：Run/Debug Configurations ->VM options
2.2、配置内容(编译后的jar放到根目录下)：-javaagent:E:\itstack-demo-javaagent-1.0-SNAPSHOT.jar=agentargs
代码示例
itstack-demo-javaagent ├── pom.xml └── src └── main ├── java │ └── org.itstack.demo.agent │ ├── MyAgent.java │ └── MyTransformer.java ├── resources │ ├── META-INF │ │ └── MANIFEST.MF │ └── log4j2.xml └── test └── java └── org.itstack.demo.test └── AgentTest.java
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"> <modelVersion>4.0.0</modelVersion> <groupId>com.jd.jr.test</groupId> <artifactId>baitiao-test-javaagent</artifactId> <version>1.0-SNAPSHOT</version> <name>test-javaagent</name> <description>test-javaagent</description> <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> <maven.configuration.manifestFile>src/main/resources/META-INF/MANIFEST.MF</maven.configuration.manifestFile> </properties> <dependencies> <dependency> <groupId>org.javassist</groupId> <artifactId>javassist</artifactId> <version>3.22.0-GA</version> </dependency> </dependencies> <build> <sourceDirectory>src/main/java</sourceDirectory> <resources> <resource> <directory>src/main/resources</directory> <filtering>true</filtering> <includes> <include>**/**</include> </includes> </resource> </resources> <testSourceDirectory>src/test/java</testSourceDirectory> <testResources> <testResource> <directory>src/test/resources</directory> <filtering>true</filtering> <includes> <include>**/**</include> </includes> </testResource> </testResources> <plugins> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-jar-plugin</artifactId> <version>2.4</version> <configuration> <archive> <manifestFile>${maven.configuration.manifestFile}</manifestFile> </archive> </configuration> </plugin> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-resources-plugin</artifactId> <version>2.5</version> <configuration> <encoding>${project.build.sourceEncoding}</encoding> </configuration> </plugin> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-compiler-plugin</artifactId> <version>2.3.2</version> <configuration> <source>1.6</source> <target>1.6</target> <encoding>${project.build.sourceEncoding}</encoding> </configuration> </plugin> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-source-plugin</artifactId> <version>2.1.2</version> <executions> <execution> <id>attach-sources</id> <goals> <goal>jar</goal> </goals> </execution> </executions> </plugin> </plugins> </build> <profiles> <profile> <id>production</id> <activation> <activeByDefault>true</activeByDefault> <jdk>1.6</jdk> </activation> <properties> <maven.compiler.source>1.6</maven.compiler.source> <maven.compiler.target>1.6</maven.compiler.target> <maven.compiler.compilerVersion>1.6</maven.compiler.compilerVersion> </properties> </profile> </profiles> </project>
MyAgent.java
package org.itstack.demo.agent; import java.lang.instrument.Instrumentation; 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) { inst.addTransformer(new MyTransformer()); } //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) { } }
MyTransformer.java
package org.itstack.demo.agent; import javassist.ClassPool; import javassist.CtClass; import javassist.CtMethod; import javassist.CtNewMethod; import java.lang.instrument.ClassFileTransformer; import java.lang.instrument.IllegalClassFormatException; import java.security.ProtectionDomain; import java.util.ArrayList; import java.util.HashMap; import java.util.List; import java.util.Map; public class MyTransformer implements ClassFileTransformer { private final static String prefix = "\nlong startTime = System.currentTimeMillis();\n"; private final static String postfix = "\nlong endTime = System.currentTimeMillis();\n"; // 被处理的方法列表 private final static Map<String, List<String>> methodMap = new HashMap<String, List<String>>(); public MyTransformer() { //对指定方法监控 add("org.itstack.demo.test.AgentTest.queryUserAge"); add("org.itstack.demo.test.AgentTest.queryUserName"); } private void add(String methodString) { String className = methodString.substring(0, methodString.lastIndexOf(".")); String methodName = methodString.substring(methodString.lastIndexOf(".") + 1); List<String> list = methodMap.get(className); if (list == null) { list = new ArrayList<String>(); methodMap.put(className, list); } list.add(methodName); } @Override public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException { className = className.replace("/", "."); // 判断加载的class的包路径是不是需要监控的类 if (methodMap.containsKey(className)) { CtClass ctclass = null; try { ctclass = ClassPool.getDefault().get(className);// 使用全称,用于取得字节码类<使用javassist> for (String methodName : methodMap.get(className)) { String outputStr = "\nSystem.out.println(\"监控信息(执行耗时)：" + className + "." + methodName + " => \" +(endTime - startTime) +\"毫秒\");"; CtMethod ctmethod = ctclass.getDeclaredMethod(methodName);// 得到这方法实例 String newMethodName = methodName + "$new";// 新定义一个方法叫做比如queryUserAge$new ctmethod.setName(newMethodName);// 将原来的方法名字修改 // 创建新的方法，复制原来的方法，名字为原来的名字 CtMethod newMethod = CtNewMethod.copy(ctmethod, methodName, ctclass, null); // 构建新的方法体 StringBuilder methodBodyStr = new StringBuilder(); methodBodyStr.append("{"); methodBodyStr.append(prefix); methodBodyStr.append(newMethodName + "($$);\n");// 调用原有代码，类似于method();($$)表示所有的参数 methodBodyStr.append(postfix); methodBodyStr.append(outputStr); methodBodyStr.append("}"); newMethod.setBody(methodBodyStr.toString());// 替换新方法 ctclass.addMethod(newMethod); // 增加新方法 } return ctclass.toBytecode(); } catch (Exception e) { e.printStackTrace(); } } return null; } }
MANIFEST.MF
Manifest-Version: 1.0 Premain-Class: org.itstack.demo.agent.MyAgent Can-Redefine-Classes: true
AgentTest.java
package org.itstack.demo.test; import java.util.logging.Logger; /** * vm options = -javaagent:E:\itstack-demo-javaagent-1.0-SNAPSHOT.jar=agentargs */ public class AgentTest { private static Logger logger = Logger.getLogger("AgentTest"); public static void main(String[] args) { String userId = "100001"; queryUserAge(userId); queryUserName(userId); } private static void queryUserAge(String userId) { try { Thread.sleep(300); logger.info("hello userId：" + userId +" age 18"); } catch (InterruptedException e) { e.printStackTrace(); } } private static void queryUserName(String userId) { try { Thread.sleep(100); logger.info("hello userId：" + userId +" name agent"); } catch (InterruptedException e) { e.printStackTrace(); } } }
测试结果
2019-4-17 11:34:33 org.itstack.demo.test.AgentTest queryUserAge$new 信息: hello userId：100001 age 18 监控信息(执行耗时)：org.itstack.demo.test.AgentTest.queryUserAge => 316毫秒 2019-4-17 11:34:33 org.itstack.demo.test.AgentTest queryUserName$new 信息: hello userId：100001 name agent 监控信息(执行耗时)：org.itstack.demo.test.AgentTest.queryUserName => 100毫秒