Java 自动化探针技术的核心原理和实践

  /*   64 : Get Method Name (and Signature) */  jvmtiError (JNICALL *GetMethodName) (jvmtiEnv* env,    jmethodID method,    char** name_ptr,    char** signature_ptr,    char** generic_ptr);

  /*   65 : Get Method Declaring Class */  jvmtiError (JNICALL *GetMethodDeclaringClass) (jvmtiEnv* env,    jmethodID method,    jclass* declaring_class_ptr);

  /*   66 : Get Method Modifiers */  jvmtiError (JNICALL *GetMethodModifiers) (jvmtiEnv* env,    jmethodID method,    jint* modifiers_ptr);

  /*   152 : Retransform Classes */  jvmtiError (JNICALL *RetransformClasses) (jvmtiEnv* env,    jint class_count,    const jclass* classes);

// class_count - pre-checked to be greater than or equal to 0// class_definitions - pre-checked for NULLjvmtiError JvmtiEnv::RedefineClasses(jint class_count, const jvmtiClassDefinition* class_definitions) {//TODO: add locking  VM_RedefineClasses op(class_count, class_definitions, jvmti_class_load_kind_redefine);  VMThread::execute(&op);  return (op.check_error());} /* end RedefineClasses */

//Java Agent 和目标进程一起启动模式java -javaagent:myagent.jar=mode=test Test

JNIEXPORT jint JNICALLAgent_OnLoad(JavaVM *vm, char *options, void *reserved); JNIEXPORT jint JNICALLAgent_OnAttach(JavaVM* vm, char* options, void* reserved);

JNIEXPORT void JNICALLAgent_OnUnload(JavaVM *vm); 

java.lang.instrument.*java.lang.instrument.Instrumentation;public interface Instrumentation {}

// 说明：添加ClassFileTransformer// 第一个参数：transformer，类转换器// 第二个参数：canRetransform，经过transformer转换过的类是否允许再次转换void Instrumentation.addTransformer(ClassFileTransformer transformer, boolean canRetransform)

// 说明：对类字节码进行增强，返回新的类字节码定义// 第一个参数：loader，类加载器// 第二个参数：className，内部定义的类全路径// 第三个参数：classBeingRedefined，待重定义/转换的类// 第四个参数：protectionDomain，保护域// 第五个参数：classfileBuffer，待重定义/转换的类字节码（不要直接在这个classfileBuffer对象上修改，需拷贝后进行）// 注：若不进行任何增强，当前方法返回null即可，若需要增强转换，则需要先拷贝一份classfileBuffer，在拷贝上进行增强转换，然后返回拷贝。byte[] ClassFileTransformer.transform(ClassLoader loader, String className, Class classBeingRedefined, ProtectionDomain protectionDomain, byte classfileBuffer)

java -javaagent:path/to/opentelemetry-javaagent.jar \     -jar myapp.jar

PreMain-Class: AgentMainCan-Redefine-Classes: trueCan-Retransform-Classes: true

// JVM启动时调用，其执行时Class 还未加载到JVMpublic static void premain(String agentArgs, Instrumentation inst);public static void premain(String agentArgs);

ClassFile {    u4             magic;           // 魔数，固定为0xCAFEBABE    u2             minor_version;   // 次版本    u2             major_version;   // 主版本，常见版本：52对应1.8，51对应1.7，其他依次类推    u2             constant_pool_count;                     // 常量池个数    cp_info        constant_pool[constant_pool_count-1];    // 常量池定义    u2             access_flags;    // 访问标志：ACC_PUBLIC, ACC_INTERFACE, ACC_ABSTRACT等    u2             this_class;      // 类索引    u2             super_class;     // 父类索引    u2             interfaces_count;    u2             interfaces[interfaces_count];    u2             fields_count;    field_info     fields[fields_count];    u2             methods_count;    method_info    methods[methods_count];    u2             attributes_count;    attribute_info attributes[attributes_count];}

public class ASMDemo extends ClassLoader{    public static <T> T getProxy(Class clazz) throws Exception {
        ClassReader classReader = new ClassReader(clazz.getName());        ClassWriter classWriter = new ClassWriter(classReader, ClassWriter.COMPUTE_MAXS);        classReader.accept(new ClassVisitor(ASM5, classWriter) {            @Override            public MethodVisitor visitMethod(int access, final String name, String descriptor, String signature, String[] exceptions) {                // 方法过滤                if (!"hi".equals(name))                    return super.visitMethod(access, name, descriptor, signature, exceptions);                final MethodVisitor methodVisitor = super.visitMethod(access, name, descriptor, signature, exceptions);                return new AdviceAdapter(ASM5, methodVisitor, access, name, descriptor) {                    @Override                    protected void onMethodEnter() {                        // 执行指令；获取静态属性                        methodVisitor.visitFieldInsn(Opcodes.GETSTATIC, "java/lang/System", "out", "Ljava/io/PrintStream;");                        // 加载常量 load constant                        methodVisitor.visitLdcInsn("方法名: "+name + "  你被代理了，By ASM！");                        // 在进入方法前，修改class，打印提示                        methodVisitor.visitMethodInsn(Opcodes.INVOKEVIRTUAL, "java/io/PrintStream", "println", "(Ljava/lang/String;)V", false);                        super.onMethodEnter();                    }                };            }        }, ClassReader.EXPAND_FRAMES);        byte[] bytes = classWriter.toByteArray();        return (T) new ASMDemo().defineClass(clazz.getName(), bytes, 0, bytes.length).newInstance();    }}  

public class HelloImpl implements Hello{    @Override    public String hi(String msg) {        return ("hello " + msg);    }}public interface Hello {    public String hi(String msg);}

Class<?> dynamicType = new ByteBuddy()  .subclass(Object.class)  .method(ElementMatchers.named("toString"))  .intercept(FixedValue.value("Hello World!"))  .make()  .load(getClass().getClassLoader())  .getLoaded();System.out.println(dynamicType.getSimpleName());// 输出：Object$ByteBuddy$ilIxkTl1

Manifest-Version: 1.0Premain-Class: com.laziobird.MyAgentDemoAgent-Class: com.laziobird.MyAgentDemoCan-Redefine-Classes: trueCan-Retransform-Classes: true

public class MyAgentDemo {    // JVM 启动时，Agent修改字节码    public static void premain(String args, Instrumentation inst) {        System.out.println(" premain agent loaded !");        inst.addTransformer(new PreMainTransformerDemo());        System.out.println(" agent addTransformer start !");    } ....   }

<dependency>   <groupId>org.javassist</groupId>   <artifactId>javassist</artifactId>   <version>3.25.0-GA</version></dependency>

public class PreMainTransformerDemo implements ClassFileTransformer{   final static String prefix = "\nlong startTime = System.currentTimeMillis();\n";   final static String postfix = "\nlong endTime = System.currentTimeMillis();\n";   @Override   public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined,                           ProtectionDomain protectionDomain, byte[] classfileBuffer){       // className 默认格式 com/laziobird 替换 com.laziobird       className = className.replace("/", ".");       //java自带的方法不进行处理,不是特别类的方法也不处理       if(className.startsWith("java") || className.startsWith("sun")|| !className.contains("com.laziobird")){           return null;       }       CtClass ctclass = null;       try {           // 使用全称,用于取得字节码类<使用javassist>           ctclass = ClassPool.getDefault().get(className);           for(CtMethod ctMethod : ctclass.getDeclaredMethods()){               String methodName = ctMethod.getName();               // 新定义一个方法叫做比如sayHello$old               String newMethodName = methodName + "$old";               // 将原来的方法名字修改               ctMethod.setName(newMethodName);               // 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 bodyStr = new StringBuilder();               bodyStr.append("{");               bodyStr.append("System.out.println(\"==============Enter Method: " + className + "." + methodName + " ==============\");");               //方法执行前，定义一个时间变量，记录方法开始前时间               bodyStr.append(prefix);               bodyStr.append(newMethodName + "($);\n");// 调用原有代码，类似于method();($)表示所有的参数               //定义方法完成时间变量               bodyStr.append(postfix);               //方法完成后，运算方法执行时间               bodyStr.append("System.out.println(\"==============Exit Method: " + className + "." + methodName + " Cost:\" +(endTime - startTime) +\"ms " + "===\");");               bodyStr.append("}");               // 新方法字节码替换原来的方法字节码               newMethod.setBody(bodyStr.toString());               ctclass.addMethod(newMethod);// 增加新方法           }           //返回新的字节流           return ctclass.toBytecode();       } catch (Exception e) {           e.printStackTrace();       }       return null;   }

package com.laziobird;public class AgentTest {    public void test() {        System.out.println("hello the method: agentTest.test ");    }    public void testB() {        ClassC c = new ClassC();        c.methodD();        System.out.println("hello the method: agentTest.testB ");    }    public static void main(String[] args) {        AgentTest agentTest = new AgentTest();        agentTest.test();        agentTest.testB();    }}package com.laziobird;public class ClassC {    public void methodD(){        try {            System.out.println(" methodD start!");            Thread.sleep(500);        } catch (InterruptedException e) {            throw new RuntimeException(e);        }    }}

java -javaagent:/path/agentdemo/target/javaagent-demo-0.0.1-SNAPSHOT-jar-with-dependencies.jar  -jar  /path/gitproject/TestAgentDemo/out/artifacts/TestAgentDemo_jar/TestAgentDemo.jar

Agent-Class: com.laziobird.MyAgentDemoCan-Redefine-Classes: trueCan-Retransform-Classes: true

void retransformClasses(Class<?>... classes) {}/**Returns whether or not the current JVM configuration supports redefinition of classes. The ability to redefine an already loaded class is an optional capability of a JVM. Redefinition will only be supported if the Can-Redefine-Classes manifest attribute is set to true in the agent JAR file (as described in the package specification) and the JVM supports this capability. During a single instantiation of a single JVM, multiple calls to this method will always return the same answer.**/

Agent-Class: com.laziobird.MyAgentDemo

public class MyAgentDemo {  // JVM运行时，Agent修改字节码  public static void agentmain(String args, Instrumentation inst) {      System.out.println(" agentmain agent loaded !");      Class[] allClass = inst.getAllLoadedClasses();      for (Class c : allClass) {          inst.addTransformer(new AgentMainTransformerDemo(), true);          try {          //agentmain 是JVM运行时，需要调用 retransformClasses 重定义类 ！！          inst.retransformClasses(c);               } catch (UnmodifiableClassException e) {                 throw new RuntimeException(e); }          }    } ....   }

public class AgentMainTransformerDemo implements ClassFileTransformer {    @Override    public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined,                            ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException {        className = className.replace("/", ".");        //这次我们用另外一种简洁API方法修改字节码        if (className.contains("com.laziobird")) {            try {                // 得到类信息                CtClass ctclass = ClassPool.getDefault().get(className);                for (CtMethod ctMethod : ctclass.getDeclaredMethods()) {                    // 方法内部声明局部变量                    ctMethod.addLocalVariable("start", CtClass.longType);                    // 方法前插入Java代码片段                    ctMethod.insertBefore("start = System.currentTimeMillis();");                    String methodName = ctMethod.getLongName();                    ctMethod.insertAfter("System.out.println(\"" + methodName + " cost: \" + (System" +                            ".currentTimeMillis() - start));");                    // 方法结束尾部插入Java代码片段                    return ctclass.toBytecode();                }            } catch (Exception e) {                e.printStackTrace();            }        }        return null;    }}

public void test(int x) {    try {        long sleepTime = x*1000;        Thread.sleep(sleepTime);        System.out.println("the method: AgentAttachTest.test | sleep time = " + sleepTime+ "ms");    } catch (InterruptedException e) {        throw new RuntimeException(e);    }}public static void main(String[] args) {    AgentAttachTest agentTest = new AgentAttachTest();    while (1==1){        int x = new Random().nextInt(10);        agentTest.test(x);    }}

public class AttachJVM {    public static void main(String[] args) throws IOException, AttachNotSupportedException, AgentLoadException, AgentInitializationException {        // 获取运行中的JVM列表        List<VirtualMachineDescriptor> vmList = VirtualMachine.list();        // 我们编写探针的Jar包路径        String agentJar = "/Users/jiangzhiwei/eclipse-workspace/agentdemo/target/javaagent-demo-0.0.1-SNAPSHOT-jar-with-dependencies.jar";        for (VirtualMachineDescriptor vmd : vmList) {            // 找到测试的JVM            System.out.println("vmd name: "+vmd.displayName());            if (vmd.displayName().endsWith("AgentAttachTest")) {                // attach到目标ID的JVM上                VirtualMachine virtualMachine = VirtualMachine.attach(vmd.id());                // agent指定jar包到已经attach的JVM上                virtualMachine.loadAgent(agentJar);                virtualMachine.detach();}}}}