网站建设文化服务公司,做app模板网站,黄岛网站开发,6生肖竞猜网站建设FieldVisitor使用abstract 修饰#xff0c;用于创建变量#xff0c;在使用时调用 ClassWriter.visitField即可创建FieldVisitor
方法介绍
visitField(Opcodes.ACC_PUBLIC, “str”, “Ljava/lang/String;”, null, “Hello World”)
第一个参数是修饰类型#xff0c;第二…FieldVisitor使用abstract 修饰用于创建变量在使用时调用 ClassWriter.visitField即可创建FieldVisitor
方法介绍
visitField(Opcodes.ACC_PUBLIC, “str”, “Ljava/lang/String;”, null, “Hello World”)
第一个参数是修饰类型第二个参数是变量名第三个是变量类型第四个签名第五个是变量的值设置值好像没什么用所以我在下面代码的初始化中重新初始化了str的值
示例代码如下
package com.example.asmapplicationimport org.junit.Test
import org.objectweb.asm.ClassWriter
import org.objectweb.asm.Opcodes
import java.io.File
import java.io.FileOutputStream
import java.net.URLClassLoaderclass DemoASMGenerateField {Testfun generate() {val filePath E:\\Develop\\ASMApplication2\\app\\src\\test\\java\\com\\example\\asmapplication\\generate\\GenerateField.classval file File(filePath)if (!file.parentFile.exists()) {file.parentFile.mkdir()}//创建ClassWriterval cw ClassWriter(ClassWriter.COMPUTE_FRAMES)//设定包名和类名cw.visit(Opcodes.V1_8,Opcodes.ACC_PUBLIC,com/example/asmapplication/generate/GenerateField,null,java/lang/Object,null)//创建全局变量val vfStr cw.visitField(Opcodes.ACC_PUBLIC, str, Ljava/lang/String;, null, Hello World)vfStr.visitEnd()//每个classFile都有一个init的初始化方法val mvInit cw.visitMethod(Opcodes.ACC_PUBLIC, init, ()V, null, null)mvInit.visitCode()mvInit.visitVarInsn(Opcodes.ALOAD, 0)mvInit.visitMethodInsn(Opcodes.INVOKESPECIAL, java/lang/Object, init, ()V, false)mvInit.visitVarInsn(Opcodes.ALOAD, 0)//初始化定义的变量的值mvInit.visitLdcInsn(Hello World)mvInit.visitFieldInsn(Opcodes.PUTFIELD, com/example/asmapplication/generate/GenerateField, str, Ljava/lang/String;)mvInit.visitInsn(Opcodes.RETURN)mvInit.visitMaxs(0, 0)mvInit.visitEnd()//创建一个test()方法val mvTest cw.visitMethod(Opcodes.ACC_PUBLIC, test, ()V, null, null)mvTest.visitCode()//打印Hello WordmvTest.visitVarInsn(Opcodes.ALOAD, 0);mvTest.visitFieldInsn(Opcodes.GETFIELD,com/example/asmapplication/generate/GenerateField,str,Ljava/lang/String;);mvTest.visitFieldInsn(Opcodes.GETSTATIC, java/lang/System, out, Ljava/io/PrintStream;)mvTest.visitInsn(Opcodes.SWAP)mvTest.visitMethodInsn(Opcodes.INVOKEVIRTUAL,java/io/PrintStream,println,(Ljava/lang/Object;)V,false)mvTest.visitInsn(Opcodes.RETURN)mvTest.visitMaxs(0, 0)mvTest.visitEnd()//类的访问结束cw.visitEnd()//输出为class文件val outputStream FileOutputStream(file)outputStream.write(cw.toByteArray())outputStream.flush()outputStream.close()val classLoader URLClassLoader(arrayOf(File(E:\\Develop\\ASMApplication2\\app\\src\\test\\java).toURI().toURL()))val clazz classLoader.loadClass(com.example.asmapplication.generate.GenerateField)val obj clazz.newInstance()clazz.getMethod(test).invoke(obj)}
}最终生成代码
//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//package com.example.asmapplication.generate;public class GenerateField {public String str Hello World;public GenerateField() {}public void test() {System.out.println(this.str);}
}技巧分享
假如我们想在MainActivity中动态生成两个变量 public int age 100;
public String str Hello World; 可以这样做
1、先在一个Test类中创建两个变量代码 如下
public class Test {public int age 100;public String str Hello World;private int sum(int i, int j) {return ij;}
}编译后通过ASM Bytecode Outline Rebooted等工具查看Test.class的字节码信息
public class com/baidu/main/test/Test {// access flags 0x1public I age// access flags 0x1public Ljava/lang/String; str// access flags 0x1public init()VALOAD 0INVOKESPECIAL java/lang/Object.init ()VALOAD 0BIPUSH 100PUTFIELD com/baidu/main/test/Test.age : IALOAD 0LDC Hello WorldPUTFIELD com/baidu/main/test/Test.str : Ljava/lang/String;RETURNMAXSTACK 2MAXLOCALS 1// access flags 0x2private sum(II)IILOAD 1ILOAD 2IADDIRETURNMAXSTACK 2MAXLOCALS 3
}对应的ASM信息如下
public class TestDump implements Opcodes {public static byte[] dump() throws Exception {ClassWriter classWriter new ClassWriter(0);FieldVisitor fieldVisitor;MethodVisitor methodVisitor;AnnotationVisitor annotationVisitor0;classWriter.visit(V1_8, ACC_PUBLIC | ACC_SUPER, com/baidu/main/test/Test, null, java/lang/Object, null);{fieldVisitor classWriter.visitField(ACC_PUBLIC, age, I, null, null);fieldVisitor.visitEnd();}{fieldVisitor classWriter.visitField(ACC_PUBLIC, str, Ljava/lang/String;, null, null);fieldVisitor.visitEnd();}{methodVisitor classWriter.visitMethod(ACC_PUBLIC, init, ()V, null, null);methodVisitor.visitCode();methodVisitor.visitVarInsn(ALOAD, 0);methodVisitor.visitMethodInsn(INVOKESPECIAL, java/lang/Object, init, ()V, false);methodVisitor.visitVarInsn(ALOAD, 0);methodVisitor.visitIntInsn(BIPUSH, 100);methodVisitor.visitFieldInsn(PUTFIELD, com/baidu/main/test/Test, age, I);methodVisitor.visitVarInsn(ALOAD, 0);methodVisitor.visitLdcInsn(Hello World);methodVisitor.visitFieldInsn(PUTFIELD, com/baidu/main/test/Test, str, Ljava/lang/String;);methodVisitor.visitInsn(RETURN);methodVisitor.visitMaxs(2, 1);methodVisitor.visitEnd();}{methodVisitor classWriter.visitMethod(ACC_PRIVATE, sum, (II)I, null, null);methodVisitor.visitCode();methodVisitor.visitVarInsn(ILOAD, 1);methodVisitor.visitVarInsn(ILOAD, 2);methodVisitor.visitInsn(IADD);methodVisitor.visitInsn(IRETURN);methodVisitor.visitMaxs(2, 3);methodVisitor.visitEnd();}classWriter.visitEnd();return classWriter.toByteArray();}
}
从ASM生成的代码中可以看到age和str两个变量后并没有立刻赋值赋值了不一定生效而是在init方法里面进行了赋值。
2.对MainActivity进行插装
package com.baidu.plugin.printimport org.objectweb.asm.AnnotationVisitor
import org.objectweb.asm.Attribute
import org.objectweb.asm.ClassVisitor
import org.objectweb.asm.FieldVisitor
import org.objectweb.asm.Label
import org.objectweb.asm.MethodVisitor
import org.objectweb.asm.Opcodes
import org.objectweb.asm.commons.AdviceAdapterclass PrintClassVisitor(nextVisitor: ClassVisitor, private val className: String): ClassVisitor(Opcodes.ASM5, nextVisitor) {override fun visit(version: Int,access: Int,name: String?,signature: String?,superName: String?,interfaces: Arrayout String?) {println(visit access $access className $className name $name signature $signature)val numFiledVisitor cv.visitField(Opcodes.ACC_PRIVATE, age, I, null, 25)numFiledVisitor.visitEnd()val strFiledVisitor cv.visitField(Opcodes.ACC_PUBLIC, str, Ljava/lang/String;, null, Hello World)strFiledVisitor.visitEnd()super.visit(version, access, name, signature, superName, interfaces)}override fun visitEnd() {super.visitEnd()}override fun visitField(access: Int,name: String?,descriptor: String?,signature: String?,value: Any?): FieldVisitor {println(visitField access $access className $className name $name descriptor $descriptor)val filedVisitor super.visitField(access, name, descriptor, signature, value)return MyPrintFieldVisitor(Opcodes.ASM5,filedVisitor)}override fun visitMethod(access: Int,name: String?,descriptor: String?,signature: String?,exceptions: Arrayout String?): MethodVisitor {val methodVisitor super.visitMethod(access, name, descriptor, signature, exceptions)return MyPrintMethodVisitor(Opcodes.ASM5,methodVisitor,access,className,name,descriptor)}}class MyPrintFieldVisitor(api: Int, filedVisitor: FieldVisitor) : FieldVisitor(api, filedVisitor) {override fun visitAnnotation(descriptor: String?, visible: Boolean): AnnotationVisitor {println(visitAnnotation descriptor $descriptor visible $visible)return super.visitAnnotation(descriptor, visible)}}class MyPrintMethodVisitor(api: Int,methodVisitor: MethodVisitor?,private val access: Int,private val className: String,private val name: String?,private val descriptor: String?
) : AdviceAdapter(api, methodVisitor, access, name, descriptor) {override fun onMethodEnter() {println(onMethodEnter access $access className $className name $name descriptor $descriptor)if (name.equals(init) descriptor.equals(()V)) {//每个classFile都有一个init的初始化方法(固定写法)mv.visitVarInsn(Opcodes.ALOAD, 0)mv.visitMethodInsn(Opcodes.INVOKESPECIAL, java/lang/Object, init, ()V, false)mv.visitVarInsn(Opcodes.ALOAD, 0)//初始化定义的变量的值mv.visitIntInsn(BIPUSH, 100)mv.visitFieldInsn(PUTFIELD, com/baidu/main/MainActivity, age, I )//String的初始化会在构造方法中mv.visitVarInsn(Opcodes.ALOAD, 0)mv.visitLdcInsn(Hello World)mv.visitFieldInsn(PUTFIELD, com/baidu/main/MainActivity, str, Ljava/lang/String )mv.visitInsn(RETURN)}if (name.equals(sum999)) {//System.out.println(999999);mv.visitFieldInsn(Opcodes.GETSTATIC, java/lang/System, out, Ljava/io/PrintStream;);mv.visitLdcInsn(999999-begin)mv.visitMethodInsn(Opcodes.INVOKEVIRTUAL, java/io/PrintStream, println, (Ljava/lang/String;)V, false);}super.onMethodEnter()}override fun onMethodExit(opcode: Int) {println(onMethodExit access $access className $className name $name descriptor $descriptor)if (name.equals(sum999)) {//System.out.println(999999);mv.visitFieldInsn(Opcodes.GETSTATIC, java/lang/System, out, Ljava/io/PrintStream;);mv.visitLdcInsn(999999-end)mv.visitMethodInsn(Opcodes.INVOKEVIRTUAL, java/io/PrintStream, println, (Ljava/lang/String;)V, false);}super.onMethodExit(opcode)}override fun visitFieldInsn(opcode: Int, owner: String?, name: String?, descriptor: String?) {println(visitFieldInsn opcode $opcode owner $owner name $name descriptor $descriptor)super.visitFieldInsn(opcode, owner, name, descriptor)}override fun visitLocalVariable(name: String?,descriptor: String?,signature: String?,start: Label?,end: Label?,index: Int) {println(visitLocalVariable name $name descriptor $descriptor start $start end $end index $index)super.visitLocalVariable(name, descriptor, signature, start, end, index)}override fun visitAttribute(attribute: Attribute?) {println(visitAttribute attribute $attribute)super.visitAttribute(attribute)}override fun visitLineNumber(line: Int, start: Label?) {println(visitLineNumber line $line start $start)super.visitLineNumber(line, start)}override fun visitFrame(type: Int,numLocal: Int,local: Arrayout Any?,numStack: Int,stack: Arrayout Any?) {println(visitFrame type $type numLocal $numLocal local $local numStack $numStack stack $stack)super.visitFrame(type, numLocal, local, numStack, stack)}override fun visitLabel(label: Label?) {println(visitLabel label $label)super.visitLabel(label)}override fun visitCode() {println(visitCode)super.visitCode()}override fun visitMaxs(maxStack: Int, maxLocals: Int) {println(visitMaxs maxStack $maxStack maxLocals $maxLocals)super.visitMaxs(maxStack, maxLocals)}override fun visitEnd() {println(visitEnd)super.visitEnd()}
}关键代码如下
创建变量
override fun visit(version: Int,access: Int,name: String?,signature: String?,superName: String?,interfaces: Arrayout String?) {println(visit access $access className $className name $name signature $signature)val numFiledVisitor cv.visitField(Opcodes.ACC_PRIVATE, age, I, null, 25)numFiledVisitor.visitEnd()val strFiledVisitor cv.visitField(Opcodes.ACC_PUBLIC, str, Ljava/lang/String;, null, Hello World)strFiledVisitor.visitEnd()super.visit(version, access, name, signature, superName, interfaces)} 注意 cv.visitField(Opcodes.ACC_PUBLIC, str, Ljava/lang/String;, null, Hello World)也给变量赋值了但是没有生效。 在init方法中给变量赋值 override fun onMethodEnter() {println(onMethodEnter access $access className $className name $name descriptor $descriptor)if (name.equals(init) descriptor.equals(()V)) {//每个classFile都有一个init的初始化方法(固定写法)mv.visitVarInsn(Opcodes.ALOAD, 0)mv.visitMethodInsn(Opcodes.INVOKESPECIAL, java/lang/Object, init, ()V, false)mv.visitVarInsn(Opcodes.ALOAD, 0)//初始化定义的变量的值mv.visitIntInsn(BIPUSH, 100)mv.visitFieldInsn(PUTFIELD, com/baidu/main/MainActivity, age, I )//String的初始化会在构造方法中mv.visitVarInsn(Opcodes.ALOAD, 0)mv.visitLdcInsn(Hello World)mv.visitFieldInsn(PUTFIELD, com/baidu/main/MainActivity, str, Ljava/lang/String )mv.visitInsn(RETURN)}super.onMethodEnter()}
如果不会写可以参考Test.class的ASM生成代码直接照抄就行。
插桩后的代码如下
package com.baidu.main;import android.os.Bundle;
import androidx.activity.ComponentActivity;
import kotlin.Metadata;/* compiled from: MainActivity.kt */
Metadata(d1 {\u0000\n\u0002\u0018\u0002\n\u0002\u0018\u0002\n\u0002\b\u0002\n\u0002\u0010\u0002\n\u0000\n\u0002\u0018\u0002\n\u0000\n\u0002\u0010\b\n\u0002\b\u0005\n\u0002\u0010\t\n\u0000\u0018\u00002\u00020\u0001B\u0005¢\u0006\u0002\u0010\u0002J\u0012\u0010\u0003\u001a\u00020\u00042\b\u0010\u0005\u001a\u0004\u0018\u00010\u0006H\u0014J\u0018\u0010\u0007\u001a\u00020\b2\u0006\u0010\t\u001a\u00020\b2\u0006\u0010\n\u001a\u00020\bH\u0002J\u0018\u0010\u000b\u001a\u00020\b2\u0006\u0010\t\u001a\u00020\b2\u0006\u0010\n\u001a\u00020\bH\u0002J\u0010\u0010\f\u001a\u00020\u00042\u0006\u0010\r\u001a\u00020\u000eH\u0002¨\u0006\u000f}, d2 {Lcom/baidu/main/MainActivity;, Landroidx/activity/ComponentActivity;, ()V, onCreate, , savedInstanceState, Landroid/os/Bundle;, sum, , i, j, sum999, test, time, , app_debug}, k 1, mv {1, 8, 0}, xi 48)
/* loaded from: classes4.dex */
public final class MainActivity extends ComponentActivity {private int age 100;public String str;public MainActivity() {this.str Hello World;}/* access modifiers changed from: protected */Override // androidx.activity.ComponentActivity, androidx.core.app.ComponentActivity, android.app.Activitypublic void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);test(100);sum(1, 2);}private final void test(long time) {Thread.sleep(time);}private final int sum(int i, int j) {return i j;}private final int sum999(int i, int j) {System.out.println(999999-begin);int i2 i j;System.out.println(999999-end);return i2;}
}
