javaagent笔记及一个基于javassit的应用监控程序demo

javaagent基本用法

1. 定义入口premain

   public static void premain(String agentArgs, Instrumentation inst) {
       System.out.println("Hello, world! JavaAgent");
       System.out.println("agentArgs: " + agentArgs);
   
       inst.addTransformer(new APMAentV1());
   }
   

2. 设置

   <build>
       <plugins>
           <plugin>
               <groupId>org.apache.maven.plugins</groupId>
               <artifactId>maven-jar-plugin</artifactId>
               <version>2.6</version>
               <configuration>
                   <archive>
                       <manifestEntries>
                           <Premain-Class>com.liq.app2.APMAgentV1</Premain-Class>
                       </manifestEntries>
                   </archive>
               </configuration>
           </plugin>
       </plugins>
   </build>
   

3. 定义转换器对class进行处理

   public class APMAentV1 implements ClassFileTransformer {
       @Override
       public byte[] transform(ClassLoader classLoader, String className, Class<?> classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException {
           ...
       }
   }
   

4. 给目标程序的启动增加-javaagent参数

   -javaagent:/home/xxx/code/app2-1.0-SNAPSHOT.jar=javaagentArg1,javaagentArg2
   # 后面的javaagentArg1,javaagentArg2会传入premain的agentArgs
   

   这样，目标程序就会加载这个javaagent了

Javassit

javassit是一个开源的分析、编辑和创建Java字节码的工具。

优点：简单、快速，不需要了解虚拟机指令。

类似的工具还有ASM。

比较而言，javassit性能没有ASM高，所以一般可以使用javaassit实现功能之后，再基于ASM去优化性能。

javaassit使用步骤：

1. 构造ClassPool对象；

2. 插入类查找路径：insertClassPath();

3. 获取CTclass；

   1. 构建新类makeClass；
   2. get加载已有类（找不到会报NotFound异常）；

4. 修改：

   1. 修改方法，如addMethod；
   2. 修改字段，如addField；
   3. 等等；

5. 生成类并装载class：

   1. toClass；
   2. toByteCode；

6. 例子

   import javassist.*;
   
   public class JavaSsistDemo1 {
       public static void main(String[] args) throws NotFoundException, CannotCompileException, IllegalAccessException, InstantiationException {
           ClassPool pool = new ClassPool(true);
           pool.insertClassPath(new LoaderClassPath(JavaSsistDemo1.class.getClassLoader()));
   
           CtClass targetClass = pool.makeClass("com.liq.Hello");
           targetClass.addInterface(pool.get(IHello.class.getName()));
           String methodName = "sayHello";
           CtClass returnType = pool.get(void.class.getName());
           CtClass[] parameters = new CtClass[]{pool.get(String.class.getName())};
           CtMethod method = new CtMethod(returnType, methodName, parameters, targetClass);
   
           String src = "{" +
                   "System.out.println(\"Hello \" + $1);" +
                   "}";
           method.setBody(src);
           targetClass.addMethod(method);
   
           Class cls = targetClass.toClass();
           IHello hello = (IHello) cls.newInstance();
           hello.sayHello("Tom");
       }
   
       public interface IHello {
           void sayHello(String name);
       }
   }
   
   

基于Javassit的一个简单应用程序监控的javaagent的完整简单例子

1. APMAgentV1.java

   package com.liq.app2;
   
   import com.liq.javaagent.collector.*;
   import javassist.ClassPool;
   import javassist.CtClass;
   import javassist.LoaderClassPath;
   
   import java.lang.instrument.ClassFileTransformer;
   import java.lang.instrument.IllegalClassFormatException;
   import java.lang.instrument.Instrumentation;
   import java.security.ProtectionDomain;
   import java.util.Map;
   import java.util.concurrent.ConcurrentHashMap;
   
   public class APMAgentV1 implements ClassFileTransformer {
   
       private static Collector[] collectors;
   
       static {
           collectors = new Collector[]{OtherCollector.INSTANCE};
       }
   
       private Map<ClassLoader, ClassPool> classPoolMap = new ConcurrentHashMap<>();
   
       @Override
       public byte[] transform(ClassLoader classLoader, String className, Class<?> classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException {
           if ((className == null) || (classLoader == null) || (classLoader.getClass().getName().equals("sun.reflect.DelegatingClassLoader")) || (classLoader.getClass().getName().equals("org.apache.catalina.loader.StandardClassLoader")) || (classLoader.getClass().getName().equals("javax.management.remote.rmi.NoCallStackClassLoader")) || (classLoader.getClass().getName().equals("com.alibaba.fastjson.util.ASMClassLoader")) || (className.indexOf("$Proxy") != -1) || (className.startsWith("java"))) {
               return null;
           }
   
           // 不同的ClassLoader使用不同的ClassPool
           ClassPool localClassPool;
           if (!this.classPoolMap.containsKey(classLoader)) {
               localClassPool = new ClassPool();
               localClassPool.insertClassPath(new LoaderClassPath(classLoader));
               this.classPoolMap.put(classLoader, localClassPool);
           } else {
               localClassPool = this.classPoolMap.get(classLoader);
           }
   
           try {
               className = className.replaceAll("/", ".");
               CtClass localCtClass = localClassPool.get(className);
               for (Collector collector : collectors) {
                   if (collector.isTarget(className, classLoader, localCtClass)) {
                       byte[] arrayOfByte = collector.transform(classLoader, className, classfileBuffer, localCtClass);
                       System.out.println(String.format("%s APM agent insert success", new Object[]{className}));
                       return arrayOfByte;
                   }
               }
           } catch (Throwable localThrowable) {
               new Exception(String.format("%s APM agent insert fail", new Object[]{className}), localThrowable).printStackTrace();
           }
           return new byte[0];
       }
   
       public static void premain(String agentArgs, Instrumentation inst) {
           System.out.println("Hello, world! JavaAgen");
           System.out.println("agentArgs: " + agentArgs);
   
           inst.addTransformer(new APMAgentV1());
       }
   }
   
   

2. ClassWrapper.java
   
   用于向目标类插入一些监控代码

   package com.liq.app2;
   
   import javassist.CtMethod;
   import javassist.NotFoundException;
   
   public class ClassWrapper {
       private String beginSrc;
       private String endSrc;
       private String errorSrc;
   
       public ClassWrapper beginSrc(String paramString) {
           this.beginSrc = paramString;
           return this;
       }
   
       public ClassWrapper endSrc(String paramString) {
           this.endSrc = paramString;
           return this;
       }
   
       public ClassWrapper errorSrc(String paramString) {
           this.errorSrc = paramString;
           return this;
       }
   
       public String beginSrc(CtMethod ctMethod) {
           try {
               String template = ctMethod.getReturnType().getName().equals("void")
                   ?
                   "{\n" +
                   "    %s        \n" +
                   "    try {\n" +
                   "        %s$agent($$);\n" +
                   "    } catch (Throwable e) {\n" +
                   "        %s\n" +
                   "        throw e;\n" +
                   "    }finally{\n" +
                   "        %s\n" +
                   "    }\n" +
                   "}"
                   :
                   "{\n" +
                   "    %s        \n" +
                   "    Object result=null;\n" +
                   "    try {\n" +
                   "        result=($w)%s$agent($$);\n" +
                   "    } catch (Throwable e) {\n" +
                   "        %s            \n" +
                   "        throw e;\n" +
                   "    }finally{\n" +
                   "        %s        \n" +
                   "    }\n" +
                   "    return ($r) result;\n" +
                   "}";
   
               String insertBeginSrc = this.beginSrc == null ? "" : this.beginSrc;
               String insertErrorSrc = this.errorSrc == null ? "" : this.errorSrc;
               String insertEndSrc = this.endSrc == null ? "" : this.endSrc;
               String result = String.format(template, new Object[]{insertBeginSrc, ctMethod.getName(), insertErrorSrc, insertEndSrc});
               return result;
           } catch (NotFoundException localNotFoundException) {
               throw new RuntimeException(localNotFoundException);
           }
       }
   }
   

3. ClassReplacer.java
   
   用于使用包装过的类替换目标类

   package com.liq.app2;
   
   import javassist.CannotCompileException;
   import javassist.CtClass;
   import javassist.CtMethod;
   import javassist.CtNewMethod;
   
   import java.io.IOException;
   
   public class ClassReplacer
   {
   private final String className;
   private final ClassLoader classLoader;
   private final CtClass ctClass;
   
   public ClassReplacer(String className, ClassLoader classLoader, CtClass ctClass)
   {
       this.className = className;
       this.classLoader = classLoader;
       this.ctClass = ctClass;
   }
   
   public void replace(CtMethod ctMethod, ClassWrapper paramd) throws CannotCompileException {
       String methodName = ctMethod.getName();
       CtMethod localCtMethod2 = CtNewMethod.copy(ctMethod, methodName, this.ctClass, null);
       localCtMethod2.setName(methodName + "$agent");
       this.ctClass.addMethod(localCtMethod2);
       ctMethod.setBody(paramd.beginSrc(ctMethod));
   }
   
   public byte[] replace() throws IOException, CannotCompileException {
       return this.ctClass.toBytecode();
   }
   }
   

4. Collector.java
   
   监控信息搜集器接口

   package com.liq.app2.collector;
   
   import javassist.CtClass;
   
   public interface Collector {
   
       boolean isTarget(String className, ClassLoader classLoader, CtClass ctClass);
   
       byte[] transform(ClassLoader classLoader, String className, byte[] classfileBuffer, CtClass ctClass);
   
   }
   
   

5. OtherCollector.java
   
   监控信息搜集器实现，这里只是简单例子，所以写死了目标类名字“com.liq.service.UserService”

   package com.liq.app2.collector;
   
   import com.liq.app2.ClassReplacer;
   import com.liq.app2.ClassWrapper;
   import com.liq.app2.stat.Statistics;
   import javassist.*;
   
   public class OtherCollector implements Collector {
   
       public static final OtherCollector INSTANCE = new OtherCollector();
   
       private OtherCollector() {
       }
   
       private static final String beginSrc;
       private static final String endSrc = "inst.end(statistic);";
       private static final String errorSrc;
   
       static {
           StringBuilder stringBuilder = new StringBuilder();
           stringBuilder.append("com.liq.app2.collector.OtherCollector inst=com.liq.app2.collector.OtherCollector.INSTANCE;");
           stringBuilder.append("com.liq.app2.stat.Statistics statistic = inst.start(\"%s\");");
           beginSrc = stringBuilder.toString();
           errorSrc = "inst.error(statistic,e);";
       }
   
       @Override
       public boolean isTarget(String className, ClassLoader classLoader, CtClass ctClass) {
           return "com.liq.service.UserService".equals(className);
       }
   
       @Override
       public byte[] transform(ClassLoader classLoader, String className, byte[] classfileBuffer, CtClass ctClass) {
           try {
               ClassReplacer replacer = new ClassReplacer(className, classLoader, ctClass);
               for (CtMethod ctMethod : ctClass.getDeclaredMethods()) {
                   String str;
                   if ((Modifier.isPublic(ctMethod.getModifiers())) && (!Modifier.isStatic(ctMethod.getModifiers()) && (!Modifier.isNative(ctMethod.getModifiers())))) {
                       ClassWrapper classWrapper = new ClassWrapper();
                       classWrapper.beginSrc(String.format(beginSrc, ctMethod.getLongName()));
                       classWrapper.endSrc(endSrc);
                       classWrapper.errorSrc(errorSrc);
   
                       replacer.replace(ctMethod, classWrapper);
                   }
               }
               return replacer.replace();
           } catch (Exception e) {
               e.printStackTrace();
           }
   
           return new byte[0];
       }
   
       public Statistics start(String methodSign) {
           return new Statistics(methodSign);
       }
   
       public void end(Statistics statistics) {
           statistics.end();
       }
   
       public void error(Statistics statistics, Throwable e) {
           statistics.error(e);
       }
   }
   
   

6. Statistics

   package com.liq.app2.stat;
   
   public class Statistics {
   
       private String method;
       private long startTime;
       private long endTime;
       private Throwable error;
   
       public Statistics(String method) {
           this.method = method;
           this.startTime = System.currentTimeMillis();
       }
   
       public void end() {
           endTime = System.currentTimeMillis();
   
           System.out.println(this.toString());
       }
   
       public void error(Throwable e) {
           error = e;
       }
   
       @Override
       public String toString() {
           final StringBuilder sb = new StringBuilder("Statistics{");
           sb.append("method='").append(method).append('\'');
           sb.append(", startTime=").append(startTime);
           sb.append(", endTime=").append(endTime);
           sb.append(", error=").append(error);
           sb.append('}');
           return sb.toString();
       }
   }
   
   

7. maven依赖

   <dependency>
       <groupId>javassist</groupId>
       <artifactId>javassist</artifactId>
       <version>3.12.1.GA</version>
   </dependency>