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110 lines (94 loc) · 4.74 KB
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package dynamic.asm;
import clazz.MyClassLoader;
import jdk.internal.org.objectweb.asm.*;
import jdk.internal.org.objectweb.asm.commons.AdviceAdapter;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.lang.reflect.Method;
public class AsmTest {
public static void main(String[] args)throws IOException {
InputStream inputStream = AsmTest.class.getResourceAsStream("Cat.class");
ClassReader cr = new ClassReader(inputStream);//创建一个对象，接受一个被修改class类的inputStream，若只是生成class类传0
ClassWriter cw = new ClassWriter(cr, 0);//创建一个修改class类的对象，接受ClassReader对象参数，在ClassWriter构造方法中保存了对象cr的引用
ClassVisitor cv = new ChangeVisitor( cw);
// cr.accept(cv, ClassReader.EXPAND_FRAMES);//对象cr接受一个cv对象并完成class的修改
cr.accept( cv, ClassReader.SKIP_DEBUG);
byte[] code = cw.toByteArray();//返回class修改完后生成新的class字节流 // 获取修改后的 class 文件对应的字节数组
try {
FileOutputStream fos = new FileOutputStream(AsmTest.class.getResource("Cat.class").getFile()); // 将二进制流写到本地磁盘上
fos.write(code);
fos.close();
Class clazz = Class.forName("dynamic.asm.Cat");
Object personObj = clazz.newInstance();
Method nameMethod = clazz.getDeclaredMethod("sayHello", null);
nameMethod.invoke(personObj, null);
System.out.println("Success!");
} catch (Exception e) {
e.printStackTrace();
}
}
static class ChangeVisitor extends ClassVisitor {
ChangeVisitor(ClassVisitor classVisitor) {
super(Opcodes.ASM4, classVisitor);
}
@Override
public MethodVisitor visitMethod(int access, String name, String desc, String signature, String[] exceptions) {
MethodVisitor methodVisitor = super.visitMethod(access, name, desc, signature, exceptions);
if (name.equals("<init>")) {
return methodVisitor;
}
MethodVisitor superMV = super.visitMethod(access, name, desc, signature, exceptions);
return new DemoMethodVisitor(superMV, name);
}
}
static class ChangeAdapter extends AdviceAdapter {
private int startTimeId = -1;
private String methodName = null;
ChangeAdapter(int api, MethodVisitor mv, int access, String name, String desc) {
super(api, mv, access, name, desc);
methodName = name;
}
@Override
protected void onMethodEnter() {
super.onMethodEnter();
startTimeId = newLocal(Type.LONG_TYPE);
mv.visitMethodInsn(INVOKESTATIC, "java/lang/System", "currentTimeMillis", "()J", false);
mv.visitIntInsn(LSTORE, startTimeId);
}
@Override
protected void onMethodExit(int opcode) {
super.onMethodExit(opcode);
int durationId = newLocal(Type.LONG_TYPE);
mv.visitMethodInsn(INVOKESTATIC, "java/lang/System", "currentTimeMillis", "()J", false);
mv.visitVarInsn(LLOAD, startTimeId);
mv.visitInsn(LSUB);
mv.visitVarInsn(LSTORE, durationId);
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.visitLdcInsn("The cost time of " + methodName + " is ");
mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/StringBuilder", "append", "(Ljava/lang/String;)Ljava/lang/StringBuilder;", false);
mv.visitVarInsn(LLOAD, durationId);
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);
}
}
static class DemoMethodVisitor extends MethodVisitor {
private String methodName;
public DemoMethodVisitor(MethodVisitor mv, String methodName) {
super(Opcodes.ASM4, mv);
this.methodName = methodName;
}
public void visitCode() {
System.out.println("at Method ‘" + methodName + "’ Begin...");
super.visitCode();
}
public void visitEnd() {
System.out.println("at Method ‘" + methodName + "’End.");
super.visitEnd();
}
}
}