通過java agent 探針和javassist 實(shí)現(xiàn)從字節(jié)碼層面的aop功能
首先我們要?jiǎng)?chuàng)建一個(gè)探針jar包
項(xiàng)目結(jié)構(gòu)如下：
image.png
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1幅恋、創(chuàng)建入口類
package com.wan;
import java.lang.instrument.Instrumentation;
public class MyAgent {
public static void premain(String agentOpts, Instrumentation instrumentation) {
System.out.println("====premain 方法執(zhí)行===");
instrumentation.addTransformer(new InsertTransformer());
}
public static void premain(String agentOps){
System.out.println("====premain方法執(zhí)行2====");
System.out.println(agentOps);
}
public static void main(String[] args) {
// TODO Auto-generated method stub
}
}
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2骤坐、創(chuàng)建MANIFEST.MF文件埠对，指定Premain-Class類
Manifest-Version: 1.0
Premain-Class: com.wan.MyAgent
Can-Redefine-Classes: true
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3斩祭、創(chuàng)建pom文件兵多，讓maven可以將MANIFEST.MF文件打入到j(luò)ar包
<?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>org.example</groupId>
<artifactId>my-agent</artifactId>
<version>1.0-SNAPSHOT</version>
<dependencies>
<dependency>
<groupId>org.javassist</groupId>
<artifactId>javassist</artifactId>
<version>3.27.0-GA</version>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-shade-plugin</artifactId>
<version>2.4.3</version>
<executions>
<execution>
<phase>package</phase>
<goals>
<goal>shade</goal>
</goals>
<configuration>
<transformers>
<transformer
implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
<manifestEntries>
<!--指明包含 premain 方法的類名尖啡，否則打包出來的文件會(huì)找不到 MANIFEST.MF -->
<Premain-Class>com.wan.MyAgent</Premain-Class>
</manifestEntries>
</transformer>
</transformers>
</configuration>
</execution>
</executions>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>
</plugins>
</build>
</project>
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4、創(chuàng)建轉(zhuǎn)換類
主要實(shí)現(xiàn)的作用就是在TongShuaiStockController的shareStockList ()方法一開始打印出我是before,關(guān)于javassit 可以查看相關(guān)資料 javassist使用全解析
這里有個(gè)關(guān)鍵是我們通過線程獲得上下文的類加載器剩膘，不然會(huì)找不到 TongShuaiStockController類衅斩，因?yàn)轫?xiàng)目是web項(xiàng)目，使用的是自定義的類加載器
package com.wan;
import javassist.ClassPool;
import javassist.CtClass;
import javassist.CtMethod;
import javassist.LoaderClassPath;
import java.lang.instrument.ClassFileTransformer;
import java.lang.instrument.IllegalClassFormatException;
import java.security.ProtectionDomain;
public class InsertTransformer implements ClassFileTransformer {
public final String injectedClassName = "com.haier.cbs.web.controller.stock.TongShuaiStockController";
public final String methodName = "shareStockList";
// public final String injectedClassName = "com.wan.spi.Solution";
// public final String methodName = "oddEvenList";
public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException {
className = className.replace("/", ".");
// System.out.println(className);
if (className.equals(injectedClassName)) {
CtClass ctclass = null;
try {
ClassPool classPool = ClassPool.getDefault();
//使用相同的類加載器援雇，不然找不controller
classPool.appendClassPath(new LoaderClassPath(this.getClass().getClassLoader()));
ctclass = classPool.get(className);// 使用全稱,用于取得字節(jié)碼類<使用javassist>
CtMethod ctmethod = ctclass.getDeclaredMethod(methodName);// 得到這方法實(shí)例
ctmethod.insertBefore("System.out.println("我是before");");
return ctclass.toBytecode();
} catch (Exception e) {
System.out.println(e.getMessage());
e.printStackTrace();
}
}
return null;
}
}
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5矛渴、使用maven進(jìn)行打包得到j(luò)ar包
image.png
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6、在需要使用探針的項(xiàng)目中加入虛擬機(jī)啟動(dòng)參數(shù)
-javaagent:D:/workspace/my-agent/target/my-agent-1.0-SNAPSHOT.jar="1212"
這個(gè)方法就是我們要處理的方法：
image.png
在我們調(diào)用接口的時(shí)候就會(huì)先打印“我是before”惫搏。
