参考资料

用过[Arthas]的都知道，Arthas是alibaba开源的一个非常强大的Java诊断工具。

不管是线上还是线下，我们都可以用Arthas分析程序的线程状态、查看jvm的实时运行状态、打印方法的出入参和返回类型、收集方法中每个代码块耗时，

甚至可以监控类、方法的调用次数、成功次数、失败次数、平均响应时长、失败率等。

前几天学习java动态字节码技术时，突然想起这款java诊断工具的trace功能：打印方法中每个节点的调用耗时。简简单单的，正好拿来做动态字节码入门学习的demo。

程序结构

src

├── agent-package.bat

├── java

│ ├── asm

│ │ ├── MANIFEST.MF

│ │ ├── TimerAgent.java

│ │ ├── TimerAttach.java

│ │ ├── TimerMethodVisitor.java

│ │ ├── TimerTrace.java

│ │ └── TimerTransformer.java

│ └── demo

│ ├── MANIFEST.MF

│ ├── Operator.java

│ └── Test.java

├── run-agent.bat

├── target-package.bat

└── tools.jar

编写目标程序

代码

package com.gravel.demo.test.asm;

/**

* @Auther: syh

* @Date: 2020/10/12

* @Description:

*/

public class Test {

public static boolean runnable = true;

public static void main(String[] args) throws Exception {

while (runnable) {

test();

}

}

// 目标：分析这个方法中每个节点的耗时

public static void test() throws Exception {

Operator.handler();

long time_wait = (long) ((Math.random() * 1000) + 2000);

Operator.callback();

Operator.pause(time_wait);

}

}

Operator.java

/**

* @Auther: syh

* @Date: 2020/10/28

* @Description: 辅助类，同样可用于分析耗时

*/

public class Operator {

public static void handler() throws Exception {

long time_wait = (long) ((Math.random() * 10) + 20);

sleep(time_wait);

}

public static void callback() throws Exception {

long time_wait = (long) ((Math.random() * 10) + 20);

sleep(time_wait);

}

public static void pause(long time_wait) throws Exception {

sleep(time_wait);

}

public static void stop() throws Exception {

Test.runnable = false;

System.out.println("business stopped.");

}

private static void sleep(long time_wait) throws Exception {

Thread.sleep(time_wait);

}

}

MANIFEST.MF

编写MANIFEST.MF文件，指定main-class。注意：冒号后面加空格，结尾加两行空白行。

Manifest-Version: 1.0

Archiver-Version: Plexus Archiver

Built-By: syh

Created-By: Apache Maven

Build-Jdk: 1.8.0_202

Main-Class: com.gravel.demo.test.asm.Target

打包

偷懒写了bat批命令，生成target.jar

@echo off & setlocal

attrib -s -h -r -a /s /d demo

rd /s /q demo

rd /q target.jar

javac -encoding utf-8 -d . ./java/demo/*.java

jar cvfm target.jar ./java/demo/MANIFEST.MF demo

rd /s /q demo

pause

java -jar target.jar

java agent探针

instrument 是 JVM 提供的一个可以修改已加载类文件的类库。而要实现代码的修改，我们需要实现一个 instrument agent。

jdk1.5时，agent有个内定方法premain。是在类加载前修改。所以无法做到修改正在运行的类。

jdk1.6后，agent新增了agentmain方法。agentmain是在虚拟机启动以后加载的。所以可以做拦截、热部署等。

讲JAVA探针技术，实际上我自己也是半吊子。所以这里用的是边分析别人例子边摸索的思路来实现我的简单的trace功能。

例子使用的是ASM字节码生成框架

MANIFEST.MF

首先一个可用的jar，关键之一是MAINFEST.MF文件是吧。

Manifest-Version: 1.0

Archiver-Version: Plexus Archiver

Created-By: Apache Maven

Built-By: syh

Build-Jdk: 1.8.0_202

Agent-Class: asm.TimerAgent

Can-Retransform-Classes: true

Can-Redefine-Classes: true

Class-Path: ./tools.jar

Main-Class: asm.TimerAttach

我们从MANIFEST.MF中提取几个关键的属性

属性

说明

Agent-Class

agentmain入口类

Premain-Class

premain入口类，与agent-class至少指定一个。

Can-Retransform-Classes

对于已经加载的类重新进行转换处理，即会触发重新加载类定义。

Can-Redefine-Classes

对已经加载的类不做转换处理，而是直接把处理结果(bytecode)直接给JVM

Class-Path

asm动态字节码技术依赖tools.jar，如果没有可以从jdk的lib目录下拷贝。

Main-Class

这里并不是agent的关键属性，为了方便，我把加载虚拟机的程序和agent合并了。

代码

然后我们来看看两个入口类，首先分析一个可执行jar的入口类Main-Class。

public class TimerAttach {

public static void main(String[] args) throws Exception {

/**

* 启动jar时，需要指定两个参数：1目标程序的pid。 2 要修改的类路径及方法，格式 package.class#methodName

*/

if (args.length < 2) {

System.out.println("pid and class must be specify.");

return;

}

if (!args[1].contains("#")) {

System.out.println("methodName must be specify.");

return;

}

VirtualMachine vm = VirtualMachine.attach(args[0]);

// 这里为了方便我把 vm和agent整合在一个jar里面了， args[1]就是agentmain的入参。

vm.loadAgent("agent.jar", args[1]);

}

}

代码很简单，1：args入参校验；2：加载目标进程pid(args[0])；3：加载agent jar包(因为合并了，所以这个jar其实就是自己)。

其中vm.loadAgent(agent.jar, args[1])会调用agent-class中的agentmain方法，而args[1]就是agentmain的第一个入参。

public class TimerAgent {

public static void agentmain(String agentArgs, Instrumentation inst) {

String[] ownerAndMethod = agentArgs.split("#");

inst.addTransformer(new TimerTransformer(ownerAndMethod[1]), true);

try {

inst.retransformClasses(Class.forName(ownerAndMethod[0]));

System.out.println("agent load done.");

} catch (Exception e) {

e.printStackTrace();

System.out.println("agent load failed!");

}

}

}

在 agentmain 方法里，我们调用retransformClassess方法载入目标类，调用addTransformer方法加载TimerTransformer类实现对目标类的重新定义。

类转换器

public class TimerTransformer implements ClassFileTransformer {

private String methodName;

public TimerTransformer(String methodName) {

this.methodName = methodName;

}

@Override

public byte[] transform(ClassLoader loader, String className, Class> classBeingRedefined, ProtectionDomain protectionDomain, byte[] classFileBuffer) {

ClassReader reader = new ClassReader(classFileBuffer);

ClassWriter classWriter = new ClassWriter(ClassWriter.COMPUTE_MAXS);

ClassVisitor classVisitor = new TimerTrace(Opcodes.ASM5, classWriter, methodName);

reader.accept(classVisitor, ClassReader.EXPAND_FRAMES);

return classWriter.toByteArray();

}

}

对被匹配到的类中的方法进行修改

public class TimerTrace extends ClassVisitor implements Opcodes {

private String owner;

private boolean isInterface;

private String methodName;

public TimerTrace(int i, ClassVisitor classVisitor, String methodName) {

super(i, classVisitor);

this.methodName = methodName;

}

@Override

public void visit(int version, int access, String name, String signature, String superName, String[] interfaces) {

super.visit(version, access, name, signature, superName, interfaces);

owner = name;

isInterface = (access & ACC_INTERFACE) != 0;

}

@Override

public MethodVisitor visitMethod(int access, String name, String descriptor, String signature,

String[] exceptions) {

MethodVisitor mv = super.visitMethod(access, name, descriptor, signature, exceptions);

// 匹配到指定methodName时，进行字节码修改

if (!isInterface && mv != null && name.equals(methodName)) {

// System.out.println(" package.className:methodName()")

mv.visitFieldInsn(GETSTATIC, "java/lang/System", "out", "Ljava/io/PrintStream;");

mv.visitTypeInsn(NEW, "java/lang/StringBuilder");

mv.visitInsn(DUP);

mv.visitMethodInsn(INVOKESPECIAL, "java/lang/StringBuilder", "", "()V", false);

mv.visitLdcInsn(" " + owner.replace("/", ".")

+ ":" + methodName + "() ");

mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/StringBuilder", "append",

"(Ljava/lang/String;)Ljava/lang/StringBuilder;", false);

mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/StringBuilder", "toString", "()Ljava/lang/String;", false);

mv.visitMethodInsn(INVOKEVIRTUAL, "java/io/PrintStream", "println", "(Ljava/lang/String;)V", false);

// 方法代码块耗时统计并打印

TimerMethodVisitor at = new TimerMethodVisitor(owner, access, name, descriptor, mv);

return at.getLocalVariablesSorter();

}

return mv;

}

public static void main(String[] args) throws IOException {

ClassWriter cw = new ClassWriter(ClassWriter.COMPUTE_MAXS);

TraceClassVisitor tv = new TraceClassVisitor(cw, new PrintWriter(System.out));

TimerTrace addFiled = new TimerTrace(Opcodes.ASM5, tv, "test");

ClassReader classReader = new ClassReader("demo.Test");

classReader.accept(addFiled, ClassReader.EXPAND_FRAMES);

File file = new File("out/production/asm-demo/demo/Test.class");

String parent = file.getParent();

File parent1 = new File(parent);

parent1.mkdirs();

file.createNewFile();

FileOutputStream fileOutputStream = new FileOutputStream(file);

fileOutputStream.write(cw.toByteArray());

}

}

要统计方法中每行代码耗时，只需要在每一行代码的前后加上当前时间戳然后相减即可。

所以我们的代码是这么写的。

public class TimerMethodVisitor extends MethodVisitor implements Opcodes {

private int start;

private int end;

private int maxStack;

private String lineContent;

public boolean instance = false;

private LocalVariablesSorter localVariablesSorter;

private AnalyzerAdapter analyzerAdapter;

public TimerMethodVisitor(String owner, int access, String name, String descriptor, MethodVisitor methodVisitor) {

super(Opcodes.ASM5, methodVisitor);

this.analyzerAdapter = new AnalyzerAdapter(owner, access, name, descriptor, this);

localVariablesSorter = new LocalVariablesSorter(access, descriptor, this.analyzerAdapter);

}

public LocalVariablesSorter getLocalVariablesSorter() {

return localVariablesSorter;

}

/**

* 进入方法后，最先执行

* 所以我们可以在这里定义一个最开始的时间戳, 然后创建一个局部变量var_end

* Long var_start = System.nanoTime();

* Long var_end;

*/

@Override

public void visitCode() {

mv.visitCode();

mv.visitMethodInsn(INVOKESTATIC, "java/lang/System", "nanoTime", "()J", false);

mv.visitMethodInsn(INVOKESTATIC, "java/lang/Long", "valueOf", "(J)Ljava/lang/Long;", false);

start = localVariablesSorter.newLocal(Type.LONG_TYPE);

mv.visitVarInsn(ASTORE, start);

end = localVariablesSorter.newLocal(Type.LONG_TYPE);

maxStack = 4;

}

/**

* 在每行代码后面增加以下代码

* var_end = System.nanoTime();

* System.out.println("[" + String.valueOf((var_end.doubleValue() - var_start.doubleValue()) / 1000000.0D) + "ms] " + "package.className:methodName() #lineNumber");

* var_start = var_end;

* @param lineNumber

* @param label

*/

@Override

public void visitLineNumber(int lineNumber, Label label) {

super.visitLineNumber(lineNumber, label);

if (instance) {

mv.visitMethodInsn(INVOKESTATIC, "java/lang/System", "nanoTime", "()J", false);

mv.visitMethodInsn(INVOKESTATIC, "java/lang/Long", "valueOf", "(J)Ljava/lang/Long;", false);

mv.visitVarInsn(ASTORE, end);

// System.out

mv.visitFieldInsn(GETSTATIC, "java/lang/System", "out", "Ljava/io/PrintStream;");

// new StringBuilder();

mv.visitTypeInsn(NEW, "java/lang/StringBuilder");

mv.visitInsn(DUP);

mv.visitMethodInsn(INVOKESPECIAL, "java/lang/StringBuilder", "", "()V", false);

mv.visitLdcInsn(" -[");

mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/StringBuilder", "append",

"(Ljava/lang/String;)Ljava/lang/StringBuilder;", false);

mv.visitVarInsn(ALOAD, end);

mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/Long", "doubleValue", "()D", false);

mv.visitVarInsn(ALOAD, start);

mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/Long", "doubleValue", "()D", false);

mv.visitInsn(DSUB);

mv.visitLdcInsn(new Double(1000 * 1000));

mv.visitInsn(DDIV);

// String.valueOf((end - start)/1000000)

mv.visitMethodInsn(INVOKESTATIC, "java/lang/String", "valueOf", "(D)Ljava/lang/String;", false);

mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/StringBuilder", "append",

"(Ljava/lang/String;)Ljava/lang/StringBuilder;", false);

mv.visitLdcInsn("ms] ");

mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/StringBuilder", "append",

"(Ljava/lang/String;)Ljava/lang/StringBuilder;", false);

// .append("owner:methodName() #line")

mv.visitLdcInsn(this.lineContent + "#" + lineNumber);

mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/StringBuilder", "append",

"(Ljava/lang/String;)Ljava/lang/StringBuilder;", false);

// stringBuilder.toString()

mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/StringBuilder", "toString", "()Ljava/lang/String;", false);

// println stringBuilder.toString()

mv.visitMethodInsn(INVOKEVIRTUAL, "java/io/PrintStream", "println", "(Ljava/lang/String;)V", false);

// start = end

mv.visitVarInsn(ALOAD, end);

mv.visitVarInsn(ASTORE, start);

maxStack = Math.max(analyzerAdapter.stack.size() + 4, maxStack);

}

instance = true;

}

/**

* 拼接字节码内容

* @param opcode

* @param owner

* @param methodName

* @param descriptor

* @param isInterface

*/

@Override

public void visitMethodInsn(int opcode, String owner, String methodName, String descriptor, boolean isInterface) {

super.visitMethodInsn(opcode, owner, methodName, descriptor, isInterface);

if (!isInterface && opcode == Opcodes.INVOKESTATIC) {

this.lineContent = owner.replace("/", ".")

+ ":" + methodName + "() ";

}

}

@Override

public void visitMaxs(int maxStack, int maxLocals) {

super.visitMaxs(Math.max(maxStack, this.maxStack), maxLocals);

}

}

如果初学者不会改字节码。可以利用idea自带的asm插件做参考。

打包

这样，一个可执行的agent jar就写完了，然后打包

@echo off

attrib -s -h -r -a /s /d asm

rd /s /q asm

rd /q agent.jar

javac -XDignore.symbol.file=true -encoding utf-8 -d . ./java/asm/*.java

jar cvfm agent.jar ./java/asm/MANIFEST.MF asm

rd /s /q asm

exit

测试

运行目标程序 target.jar

java -jar target.jar

打印Test.test中每个节点耗时

java -jar agent.jar [pid] demo.Test#test

结果

打印Operator.handler方法每个节点耗时