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
