1.概述
在上一篇文章：【字节码】Java Instrumentation 简介 以及 ASM 组合案例 因为这篇文章我一直找不到原因，然后找到了这篇文章。
转载：JVM插码之五：Java agent+ASM实战–监控所有方法执行时间
本文建立在对instrumentation和agent有初步的了解的前提下阅读，关于这2个类的讲解在其它文章中。
这是一个maven项目，pom中需要的配置，lib中有asm的jar包
maven如下
<groupId>org.example</groupId>
<artifactId>javaagent-apiv2</artifactId>
<version>1.0-SNAPSHOT</version>
<packaging>jar</packaging>
<properties>
<maven.compiler.source>8</maven.compiler.source>
<maven.compiler.target>8</maven.compiler.target>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<asm.version>9.0</asm.version>
</properties>
<dependencies>
<dependency>
<groupId>org.ow2.asm</groupId>
<artifactId>asm-analysis</artifactId>
<version>${asm.version}</version>
</dependency>
<dependency>
<groupId>org.ow2.asm</groupId>
<artifactId>asm-commons</artifactId>
<version>${asm.version}</version>
</dependency>
<dependency>
<groupId>org.ow2.asm</groupId>
<artifactId>asm-tree</artifactId>
<version>${asm.version}</version>
</dependency>
<dependency>
<groupId>org.ow2.asm</groupId>
<artifactId>asm-util</artifactId>
<version>${asm.version}</version>
</dependency>
<dependency>
<groupId>javassist</groupId>
<artifactId>javassist</artifactId>
<version>3.12.1.GA</version>
</dependency>
<!-- https://mvnrepository.com/artifact/cglib/cglib -->
<dependency>
<groupId>cglib</groupId>
<artifactId>cglib</artifactId>
<version>3.2.5</version>
</dependency>
<!-- https://mvnrepository.com/artifact/oro/oro -->
<dependency>
<groupId>oro</groupId>
<artifactId>oro</artifactId>
<version>2.0.8</version>
</dependency>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>3.8.1</version>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<source>1.8</source>
<target>1.8</target>
<encoding>utf-8</encoding>
</configuration>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-shade-plugin</artifactId>
<version>3.0.0</version>
<executions>
<execution>
<phase>package</phase>
<goals>
<goal>shade</goal>
</goals>
<configuration>
<transformers>
<transformer
implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
<manifestEntries>
<!-- <Premain-Class>com.dxz.chama.javaagent.patter.TimeMonitorPatterAgent</Premain-Class> -->
<!-- <Premain-Class>com.dxz.chama.javaagent.StatAgent</Premain-Class> -->
<Premain-Class>com.javaagent.api.UdAgent</Premain-Class>
</manifestEntries>
</transformer>
</transformers>
</configuration>
</execution>
</executions>
</plugin>
</plugins>
</build>
</project>
agent类，只有一个方法，就是把自定义的类修改器添加到instrumentation中。
public class UdAgent {
public static void premain(String agentArgs, Instrumentation instrumentation){
instrumentation.addTransformer(new LogTransformer());
}
}
类转换器实现：
import java.io.IOException;
import java.lang.instrument.ClassFileTransformer;
import java.lang.instrument.IllegalClassFormatException;
import java.security.ProtectionDomain;
import org.objectweb.asm.ClassReader;
import org.objectweb.asm.ClassWriter;
public class LogTransformer implements ClassFileTransformer {
@Override
public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined,
ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException {
try {
ClassReader cr = new ClassReader(className);
ClassWriter cw = new ClassWriter(ClassWriter.COMPUTE_MAXS);
TimeCountAdpter timeCountAdpter = new TimeCountAdpter(cw);
cr.accept(timeCountAdpter, ClassReader.EXPAND_FRAMES);
return cw.toByteArray();
} catch (IOException e) {
e.printStackTrace();
}
return null;
}
}
实际修改字节码的方法，这里给每个类添加了一个字段UDASMCN，用于记录当前类的名字（方便打印信息）。同时记录每个方法的名字，以及执行时间。
import org.objectweb.asm.ClassVisitor;
import org.objectweb.asm.FieldVisitor;
import org.objectweb.asm.MethodVisitor;
import org.objectweb.asm.Opcodes;
import org.objectweb.asm.Type;
import org.objectweb.asm.commons.AnalyzerAdapter;
import org.objectweb.asm.commons.LocalVariablesSorter;
public class TimeCountAdpter extends ClassVisitor implements Opcodes {
private String owner;
private boolean isInterface;
private String filedName = "UDASMCN";
private int acc = Opcodes.ACC_PUBLIC + Opcodes.ACC_STATIC + Opcodes.ACC_FINAL;
private boolean isPresent = false;
private String methodName;
public TimeCountAdpter(ClassVisitor classVisitor) {
super(ASM6, classVisitor);
}
@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 FieldVisitor visitField(int access, String name, String descriptor, String signature, Object value) {
if (name.equals(filedName)) {
isPresent = true;
}
return super.visitField(access, name, descriptor, signature, value);
}
@Override
public MethodVisitor visitMethod(int access, String name, String descriptor, String signature,
String[] exceptions) {
MethodVisitor mv = cv.visitMethod(access, name, descriptor, signature, exceptions);
if (!isInterface && mv != null && !name.equals("<init>") && !name.equals("<clinit>")) {
methodName = name;
AddTimerMethodAdapter at = new AddTimerMethodAdapter(mv);
at.aa = new AnalyzerAdapter(owner, access, name, descriptor, at);
at.lvs = new LocalVariablesSorter(access, descriptor, at.aa);
return at.lvs;
}
return mv;
}
public void visitEnd() {
if (!isInterface) {
FieldVisitor fv = cv.visitField(acc, filedName, "Ljava/lang/String;", null, owner);
if (fv != null) {
fv.visitEnd();
}
}
cv.visitEnd();
}
class AddTimerMethodAdapter extends MethodVisitor {
private int time;
private int maxStack;
public LocalVariablesSorter lvs;
public AnalyzerAdapter aa;
public AddTimerMethodAdapter(MethodVisitor methodVisitor) {
super(ASM6, methodVisitor);
}
@Override
public void visitCode() {
mv.visitCode();
mv.visitMethodInsn(INVOKESTATIC, "java/lang/System", "nanoTime", "()J", false);
time = lvs.newLocal(Type.LONG_TYPE);
mv.visitVarInsn(LSTORE, time);
maxStack = 4;
}
@Override
public void visitInsn(int opcode) {
if (((opcode >= IRETURN && opcode <= RETURN) || opcode == ATHROW) && !isPresent) {
mv.visitMethodInsn(INVOKESTATIC, "java/lang/System", "nanoTime", "()J", false);
mv.visitVarInsn(LLOAD, time);
mv.visitInsn(LSUB);
mv.visitVarInsn(LSTORE, time);
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", "<init>", "()V", false);
mv.visitFieldInsn(GETSTATIC, owner, filedName, "Ljava/lang/String;");
mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/StringBuilder", "append",
"(Ljava/lang/String;)Ljava/lang/StringBuilder;", false);
mv.visitLdcInsn(" " + methodName + ":");
mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/StringBuilder", "append",
"(Ljava/lang/String;)Ljava/lang/StringBuilder;", false);
mv.visitVarInsn(LLOAD, time);
mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/StringBuilder", "append", "(J)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);
maxStack = Math.max(aa.stack.size() + 4, maxStack);
}
mv.visitInsn(opcode);
}
@Override
public void visitMaxs(int maxStack, int maxLocals) {
super.visitMaxs(Math.max(maxStack, this.maxStack), maxLocals);
}
}
}
打包成jar包后，在另一个程序启动时调用，启动参数如下：
lcc@lcc javaagent-apiv2$ java -javaagent:./target/javaagent-apiv2-1.0-SNAPSHOT.jar
java/lang/Shutdown runHooks:3294
java/lang/Shutdown sequence:43843
java/lang/Shutdown shutdown:56371
执行效果：
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14292217 查看本文章
时间单位是纳秒，可以看到每个方法执行完时，都会打印这个方法 的执行时间，以com/Main main:11457636为例，说明类com/Main的main方法执行力11毫秒。
