从0开始，整点代理类

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使用JDK、ASM生成一个代理类。

预先准备工作

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// filename: IProcess.java
package moe.xinmu.test.proxy;

public interface IProcess {
    void run();
}
// filename: InvocationHandlerImpl.java
package moe.xinmu.test.proxy;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.util.Arrays;

public class InvocationHandlerImpl implements InvocationHandler {

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        System.out.println("ProxyClass--- " + proxy.getClass());
        System.out.println("Method--- " + method);
        System.out.println("Args--- " + Arrays.toString(args));
        return null;
    }
}

用JDK代理类

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// filename: Main.java
package moe.xinmu.test.proxy;

import java.lang.reflect.Proxy;

public class Main {
    public static void main(String[] args) {
        InvocationHandlerImpl impl = new InvocationHandlerImpl();
        Object proxy = Proxy.newProxyInstance(Main.class.getClassLoader(),
                new Class[]{IProcess.class},
                impl);
        ((IProcess) proxy).run();
    }
}
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ProxyClass--- class com.sun.proxy.$Proxy0
Method--- public abstract void moe.xinmu.test.proxy.IProcess.run()
Args--- null

用ASM代理类

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// filename: ASMProxy.java
package moe.xinmu.test.proxy;

import org.objectweb.asm.ClassWriter;
import org.objectweb.asm.MethodVisitor;
import org.objectweb.asm.Opcodes;
import org.objectweb.asm.Type;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.util.*;
import java.util.concurrent.atomic.AtomicInteger;

public class ASMProxy {
    final static AtomicInteger atomic = new AtomicInteger();
    static Map<ClassLoader, ProxyClassLoader> proxyClassLoaderMap = new Hashtable<>() {
        @Override
        public synchronized ProxyClassLoader get(Object key) {
            ClassLoader classLoader = (ClassLoader) key;
            ProxyClassLoader loader = super.get(key);
            if (loader == null) {
                loader = new ProxyClassLoader(classLoader);
            }
            put(classLoader, loader);
            return loader;
        }
    };

    public static Object newProxyInstance(ClassLoader loader,
                                          Class<?>[] interfaces,
                                          InvocationHandler h) {
        try {

            //checkClassLoader
            if (loader == null) {
                throw new NullPointerException();
            }
            //checkInterfaces
            if (interfaces == null) {
                throw new NullPointerException();
            }
            //checkHandler
            if (h == null) {
                throw new NullPointerException();
            }
            String[] interfacesName = new String[interfaces.length];
            for (int i = 0; i < interfaces.length; i++) {
                Class<?> iface = interfaces[i];
                if (iface == null) {
                    throw new NullPointerException();
                }
                if (!iface.isInterface()) {
                    throw new NullPointerException();
                }
                if (loader.loadClass(iface.getName()) != iface) {
                    throw new ClassCastException();
                }
                interfacesName[i] = iface.getName().replace(".", "/");
            }
            String nClassName = ASMProxy.class.getName() + "$Proxy" + atomic.incrementAndGet();
            ProxyClassLoader proxyClassLoader = proxyClassLoaderMap.get(loader);
            ClassWriter cw = new ClassWriter(ClassWriter.COMPUTE_MAXS);
            String internalName = nClassName.replace(".", "/") ;
            cw.visit(Opcodes.V1_8,
                    Opcodes.ACC_SUPER | Opcodes.ACC_PUBLIC | Opcodes.ACC_FINAL,
                    internalName,
                    null,
                    "java/lang/Object",
                    interfacesName);
            // processAllMethod
            cw.visitField(Opcodes.ACC_FINAL | Opcodes.ACC_STATIC | Opcodes.ACC_PRIVATE, "$Method", "[Ljava/lang/reflect/Method;", null, null);
            cw.visitField(Opcodes.ACC_FINAL | Opcodes.ACC_PRIVATE, "$Handler", "Ljava/lang/reflect/InvocationHandler;", null, null);
            int methodIndex = 0;
            MethodVisitor clinitMethod = cw.visitMethod(Opcodes.ACC_PUBLIC | Opcodes.ACC_STATIC, "<clinit>", "()V", null, null);
            clinitMethod.visitFieldInsn(Opcodes.GETSTATIC, internalName, "$Methods", "I");
            clinitMethod.visitTypeInsn(Opcodes.ANEWARRAY, "java/lang/reflect/Method");
            clinitMethod.visitInsn(Opcodes.DUP);
            clinitMethod.visitFieldInsn(Opcodes.PUTSTATIC,internalName, "$Method", "[Ljava/lang/reflect/Method;");
            HashSet<String> methods = new HashSet<>();
            List<Class<?>> simClass = new ArrayList<>(Arrays.asList(interfaces));
            simClass.add(Object.class);
            for (Class<?> interfaceClass : simClass) {
                for (Method method : interfaceClass.getMethods()) {
                    if (Modifier.isStatic(method.getModifiers())) {
                        continue;
                    }
                    if (Modifier.isFinal(method.getModifiers())) {
                        continue;
                    }
                    String methodName = method.getName();
                    String methodDesc = getMethodDesc(method);
                    if (methods.contains(methodName + methodDesc)) {
                        continue;
                    }
                    methods.add(methodName + methodDesc);
                    Type[] argumentTypes = Type.getType(methodDesc).getArgumentTypes();
                    // method init
                    MethodVisitor visitor = cw.visitMethod(Opcodes.ACC_PUBLIC, methodName, methodDesc, null, null);
                    visitor.visitIntInsn(Opcodes.ALOAD, 0);
                    visitor.visitFieldInsn(Opcodes.GETFIELD,internalName, "$Handler", "Ljava/lang/reflect/InvocationHandler;");
                    visitor.visitIntInsn(Opcodes.ALOAD, 0);
                    visitor.visitFieldInsn(Opcodes.GETSTATIC, internalName, "$Method", "[Ljava/lang/reflect/Method;");
                    visitor.visitLdcInsn(methodIndex);
                    visitor.visitInsn(Opcodes.AALOAD);

                    if (argumentTypes.length == 0) {
                        visitor.visitInsn(Opcodes.ACONST_NULL);
                    } else {
                        visitor.visitLdcInsn(argumentTypes.length);
                        visitor.visitTypeInsn(Opcodes.ANEWARRAY, "java/lang/Object");
                        int iMem = 1;
                        for (int i = 0; i < argumentTypes.length; i++) {
                            visitor.visitInsn(Opcodes.DUP);
                            visitor.visitLdcInsn(i);
                            Type type = argumentTypes[i];
                            switch (type.getSort()) {
                                case Type.BOOLEAN:
                                    visitor.visitIntInsn(Opcodes.ILOAD, iMem);
                                    visitor.visitMethodInsn(Opcodes.INVOKESTATIC, "java/lang/Boolean", "valueOf", "(Z)Ljava/lang/Boolean;", false);
                                    break;
                                case Type.CHAR:
                                    visitor.visitIntInsn(Opcodes.ILOAD, iMem);
                                    visitor.visitMethodInsn(Opcodes.INVOKESTATIC, "java/lang/Character", "valueOf", "(C)Ljava/lang/Character;", false);
                                    break;
                                case Type.BYTE:
                                    visitor.visitIntInsn(Opcodes.ILOAD, iMem);
                                    visitor.visitMethodInsn(Opcodes.INVOKESTATIC, "java/lang/Byte", "valueOf", "(B)Ljava/lang/Byte;", false);
                                    break;
                                case Type.SHORT:
                                    visitor.visitIntInsn(Opcodes.ILOAD, iMem);
                                    visitor.visitMethodInsn(Opcodes.INVOKESTATIC, "java/lang/Short", "valueOf", "(S)Ljava/lang/Short;", false);
                                    break;
                                case Type.INT:
                                    visitor.visitIntInsn(Opcodes.ILOAD, iMem);
                                    visitor.visitMethodInsn(Opcodes.INVOKESTATIC, "java/lang/Integer", "valueOf", "(I)Ljava/lang/Integer;", false);
                                    break;
                                case Type.FLOAT:
                                    visitor.visitIntInsn(Opcodes.FLOAD, iMem);
                                    visitor.visitMethodInsn(Opcodes.INVOKESTATIC, "java/lang/Float", "valueOf", "(F)Ljava/lang/Float;", false);
                                    break;
                                case Type.LONG:
                                    visitor.visitIntInsn(Opcodes.LLOAD, iMem++);
                                    visitor.visitMethodInsn(Opcodes.INVOKESTATIC, "java/lang/Long", "valueOf", "(J)Ljava/lang/Long;", false);
                                    break;
                                case Type.DOUBLE:
                                    visitor.visitIntInsn(Opcodes.DLOAD, iMem++);
                                    visitor.visitMethodInsn(Opcodes.INVOKESTATIC, "java/lang/Double", "valueOf", "(D)Ljava/lang/Double;", false);
                                    break;
                                default:
                                    visitor.visitIntInsn(Opcodes.ALOAD, iMem);
                                    break;
                            }
                            visitor.visitInsn(Opcodes.AASTORE);
                            iMem++;
                        }
                    }
                    visitor.visitMethodInsn(Opcodes.INVOKEINTERFACE, "java/lang/reflect/InvocationHandler", "invoke", "(Ljava/lang/Object;Ljava/lang/reflect/Method;[Ljava/lang/Object;)Ljava/lang/Object;", true);
                    Type retType = Type.getType(methodDesc).getReturnType();
                    switch (retType.getSort()) {
                        case Type.BOOLEAN:
                            visitor.visitTypeInsn(Opcodes.CHECKCAST, "java/lang/Boolean");
                            visitor.visitMethodInsn(Opcodes.INVOKEVIRTUAL, "java/lang/Boolean", "booleanValue", "()Z", false);
                            visitor.visitInsn(Opcodes.IRETURN);
                            break;
                        case Type.CHAR:
                            visitor.visitTypeInsn(Opcodes.CHECKCAST, "java/lang/Character");
                            visitor.visitMethodInsn(Opcodes.INVOKEVIRTUAL, "java/lang/Character", "charValue", "()C", false);
                            visitor.visitInsn(Opcodes.IRETURN);
                            break;
                        case Type.BYTE:
                            visitor.visitTypeInsn(Opcodes.CHECKCAST, "java/lang/Number");
                            visitor.visitMethodInsn(Opcodes.INVOKEVIRTUAL, "java/lang/Number", "byteValue", "()B", false);
                            visitor.visitInsn(Opcodes.IRETURN);
                            break;
                        case Type.SHORT:
                            visitor.visitTypeInsn(Opcodes.CHECKCAST, "java/lang/Number");
                            visitor.visitMethodInsn(Opcodes.INVOKEVIRTUAL, "java/lang/Number", "shortValue", "()S", false);
                            visitor.visitInsn(Opcodes.IRETURN);
                            break;
                        case Type.INT:
                            visitor.visitTypeInsn(Opcodes.CHECKCAST, "java/lang/Number");
                            visitor.visitMethodInsn(Opcodes.INVOKEVIRTUAL, "java/lang/Number", "intValue", "()I", false);
                            visitor.visitInsn(Opcodes.IRETURN);
                            break;
                        case Type.FLOAT:
                            visitor.visitTypeInsn(Opcodes.CHECKCAST, "java/lang/Number");
                            visitor.visitMethodInsn(Opcodes.INVOKEVIRTUAL, "java/lang/Number", "floatValue", "()F", false);
                            visitor.visitInsn(Opcodes.FRETURN);
                            break;
                        case Type.LONG:
                            visitor.visitTypeInsn(Opcodes.CHECKCAST, "java/lang/Number");
                            visitor.visitMethodInsn(Opcodes.INVOKEVIRTUAL, "java/lang/Number", "longValue", "()L", false);
                            visitor.visitInsn(Opcodes.LRETURN);
                            break;
                        case Type.DOUBLE:
                            visitor.visitTypeInsn(Opcodes.CHECKCAST, "java/lang/Number");
                            visitor.visitMethodInsn(Opcodes.INVOKEVIRTUAL, "java/lang/Number", "doubleValue", "()D", false);
                            visitor.visitInsn(Opcodes.DRETURN);
                            break;
                        case Type.VOID:
                            visitor.visitInsn(Opcodes.POP);
                            visitor.visitInsn(Opcodes.RETURN);
                            break;
                        default:
                            visitor.visitTypeInsn(Opcodes.CHECKCAST, retType.getClassName().replace('.', '/'));
                            visitor.visitInsn(Opcodes.ARETURN);
                            break;
                    }
                    visitor.visitMaxs(0, 0);
                    visitor.visitEnd();
                    // classloader init
                    clinitMethod.visitInsn(Opcodes.DUP);
                    clinitMethod.visitLdcInsn(methodIndex);
                    clinitMethod.visitLdcInsn(Type.getType(interfaceClass));
                    clinitMethod.visitLdcInsn(method.getName());
                    clinitMethod.visitLdcInsn(argumentTypes.length);
                    clinitMethod.visitTypeInsn(Opcodes.ANEWARRAY, "java/lang/Class");
                    for (int i = 0; i < argumentTypes.length; i++) {
                        clinitMethod.visitInsn(Opcodes.DUP);
                        clinitMethod.visitLdcInsn(i);
                        typeLdc(clinitMethod, argumentTypes[i]);
                        clinitMethod.visitInsn(Opcodes.AASTORE);
                    }
                    clinitMethod.visitMethodInsn(Opcodes.INVOKEVIRTUAL, "java/lang/Class", "getDeclaredMethod", "(Ljava/lang/String;[Ljava/lang/Class;)Ljava/lang/reflect/Method;", false);
                    clinitMethod.visitInsn(Opcodes.AASTORE);
                    //end
                    methodIndex++;
                }
            }
            clinitMethod.visitInsn(Opcodes.RETURN);
            clinitMethod.visitMaxs(0, 0);
            clinitMethod.visitEnd();
            cw.visitField(Opcodes.ACC_FINAL | Opcodes.ACC_STATIC | Opcodes.ACC_PRIVATE, "$Methods", "I", null, methodIndex);
            MethodVisitor mv = cw.visitMethod(Opcodes.ACC_PUBLIC, "<init>", "(Ljava/lang/reflect/InvocationHandler;)V", null, null);
            mv.visitIntInsn(Opcodes.ALOAD, 0);
            mv.visitMethodInsn(Opcodes.INVOKESPECIAL, "java/lang/Object", "<init>", "()V", false);
            mv.visitIntInsn(Opcodes.ALOAD, 0);
            mv.visitIntInsn(Opcodes.ALOAD, 1);
            mv.visitFieldInsn(Opcodes.PUTFIELD, internalName, "$Handler", "Ljava/lang/reflect/InvocationHandler;");
            mv.visitInsn(Opcodes.RETURN);
            mv.visitMaxs(0, 0);
            mv.visitEnd();
            cw.visitEnd();
            byte[] bytes = cw.toByteArray();
            return proxyClassLoader.pDefineClass(nClassName, bytes, 0, bytes.length)
                    .getDeclaredConstructor(InvocationHandler.class)
                    .newInstance(h);
        } catch (RuntimeException e) {
            throw e;
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    public static String getMethodDesc(Method method) {
        StringBuilder builder = new StringBuilder("(");
        Class<?>[] parameters = method.getParameterTypes();
        for (Class<?> parameter : parameters) {
            builder.append(getClassName(parameter));
        }
        builder.append(")");
        builder.append(getClassName(method.getReturnType()));
        return builder.toString();
    }

    public static String getClassName(Class<?> parameter) {
        StringBuilder builder = new StringBuilder();
        if (parameter.isArray()) {
            do {
                builder.append("[");
                parameter = parameter.getComponentType();
            } while (parameter.isArray());
        }
        if (!parameter.isPrimitive()) {
            builder.append("L")
                    .append(parameter.getName().replace(".", "/"))
                    .append(";");
        } else {
            if (parameter == Boolean.TYPE) {
                builder.append("Z");
            } else if (parameter == Character.TYPE) {
                builder.append("C");
            } else if (parameter == Byte.TYPE) {
                builder.append("B");
            } else if (parameter == Short.TYPE) {
                builder.append("S");
            } else if (parameter == Integer.TYPE) {
                builder.append("I");
            } else if (parameter == Long.TYPE) {
                builder.append("J");
            } else if (parameter == Float.TYPE) {
                builder.append("F");
            } else if (parameter == Double.TYPE) {
                builder.append("D");
            } else if (parameter == Void.TYPE) {
                builder.append("V");
            } else {
                throw new RuntimeException("Unknow " + parameter);
            }
        }
        return builder.toString();
    }

    static class ProxyClassLoader extends ClassLoader {
        public ProxyClassLoader(ClassLoader parent) {
            super("ASMProxy", parent);
        }

        public Class<?> pDefineClass(String name, byte[] b, int off, int len)
                throws ClassFormatError {
            return defineClass(name, b, off, len, null);
        }
    }

    static void typeLdc(MethodVisitor mv, Type type) {
        if (type.getSort() == Type.OBJECT) {
            mv.visitLdcInsn(type);
        }
        switch (type.getSort()) {
            case Type.BOOLEAN:
                mv.visitFieldInsn(Opcodes.GETSTATIC, "java/lang/Boolean", "TYPE", "Ljava/lang/Class;");
                break;
            case Type.CHAR:
                mv.visitFieldInsn(Opcodes.GETSTATIC, "java/lang/Character", "TYPE", "Ljava/lang/Class;");
                break;
            case Type.BYTE:
                mv.visitFieldInsn(Opcodes.GETSTATIC, "java/lang/Byte", "TYPE", "Ljava/lang/Class;");
                break;
            case Type.SHORT:
                mv.visitFieldInsn(Opcodes.GETSTATIC, "java/lang/Short", "TYPE", "Ljava/lang/Class;");
                break;
            case Type.INT:
                mv.visitFieldInsn(Opcodes.GETSTATIC, "java/lang/Integer", "TYPE", "Ljava/lang/Class;");
                break;
            case Type.FLOAT:
                mv.visitFieldInsn(Opcodes.GETSTATIC, "java/lang/Float", "TYPE", "Ljava/lang/Class;");
                break;
            case Type.LONG:
                mv.visitFieldInsn(Opcodes.GETSTATIC, "java/lang/Long", "TYPE", "Ljava/lang/Class;");
                break;
            case Type.DOUBLE:
                mv.visitFieldInsn(Opcodes.GETSTATIC, "java/lang/Double", "TYPE", "Ljava/lang/Class;");
                break;
        }
    }
}
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// filename: Main.java
package moe.xinmu.test.proxy;

import java.lang.reflect.Proxy;

public class Main {
    public static void main(String[] args) {
        InvocationHandlerImpl impl = new InvocationHandlerImpl();
        Object proxy = ASMProxy.newProxyInstance(Main.class.getClassLoader(),
                new Class[]{IProcess.class},
                impl);
        ((IProcess) proxy).run();
    }
}
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ProxyClass--- class moe.xinmu.test.proxy.ASMProxy$Proxy1
Method--- public abstract void moe.xinmu.test.proxy.IProcess.run()
Args--- null