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>
posted @ 2018-08-05 23:51  liqipeng  阅读(887)  评论(0)  编辑  收藏  举报