proxyfactory.java

Javassist是一个开源的分析、编辑和创建Java字节码的类库。是由东京技术学院的数学和计算机科学系的 Shigeru Chiba 所创建的。它已加入了开放源代码JBoss 应用服务器项目,通过使

            String key = (String)it.next();
            if (key.startsWith(name))
                return false;
        }

        return true;
    }

    /**
     * Returns true if the method is visible from the class.
     *
     * @param mod       the modifiers of the method. 
     */
    private static boolean isVisible(int mod, String from, Member meth) {
        if ((mod & Modifier.PRIVATE) != 0)
            return false;
        else if ((mod & (Modifier.PUBLIC | Modifier.PROTECTED)) != 0)
            return true;
        else {
            String p = getPackageName(from);
            String q = getPackageName(meth.getDeclaringClass().getName());
            if (p == null)
                return q == null;
            else
                return p.equals(q);
        }
    }

    private static String getPackageName(String name) {
        int i = name.lastIndexOf('.');
        if (i < 0)
            return null;
        else
            return name.substring(0, i);
    }

    private static HashMap getMethods(Class superClass, Class[] interfaceTypes) {
        HashMap hash = new HashMap();
        for (int i = 0; i < interfaceTypes.length; i++)
            getMethods(hash, interfaceTypes[i]);

        getMethods(hash, superClass);
        return hash;
    }

    private static void getMethods(HashMap hash, Class clazz) {
        Class[] ifs = clazz.getInterfaces();
        for (int i = 0; i < ifs.length; i++)
            getMethods(hash, ifs[i]);

        Class parent = clazz.getSuperclass();
        if (parent != null)
            getMethods(hash, parent);

        Method[] methods = clazz.getDeclaredMethods();
        for (int i = 0; i < methods.length; i++)
            if (!Modifier.isPrivate(methods[i].getModifiers())) {
                Method m = methods[i];
                String key = m.getName() + ':' + RuntimeSupport.makeDescriptor(m);
                hash.put(key, methods[i]);
            }
    }

    private static String keyToDesc(String key) {
        return key.substring(key.indexOf(':') + 1);
    }

    private static MethodInfo makeConstructor(String thisClassName, Constructor cons,
                                              ConstPool cp, Class superClass) {
        String desc = RuntimeSupport.makeDescriptor(cons.getParameterTypes(),
                                                    Void.TYPE);
        MethodInfo minfo = new MethodInfo(cp, "<init>", desc);
        minfo.setAccessFlags(Modifier.PUBLIC);      // cons.getModifiers() & ~Modifier.NATIVE
        setThrows(minfo, cp, cons.getExceptionTypes());
        Bytecode code = new Bytecode(cp, 0, 0);

        code.addAload(0);
        code.addGetstatic(thisClassName, DEFAULT_INTERCEPTOR, HANDLER_TYPE);
        code.addOpcode(Opcode.DUP);
        code.addOpcode(Opcode.IFNONNULL);
        code.addIndex(7);
        code.addOpcode(Opcode.POP);
        code.addGetstatic(NULL_INTERCEPTOR_HOLDER, DEFAULT_INTERCEPTOR, HANDLER_TYPE);
        code.addPutfield(thisClassName, HANDLER, HANDLER_TYPE);

        code.addAload(0);
        int s = addLoadParameters(code, cons.getParameterTypes(), 1);
        code.addInvokespecial(superClass.getName(), "<init>", desc);
        code.addOpcode(Opcode.RETURN);
        code.setMaxLocals(s + 1);
        minfo.setCodeAttribute(code.toCodeAttribute());
        return minfo;
    }

    private static MethodInfo makeDelegator(Method meth, String desc,
                ConstPool cp, Class declClass, String delegatorName) {
        MethodInfo delegator = new MethodInfo(cp, delegatorName, desc);
        delegator.setAccessFlags(Modifier.FINAL | Modifier.PUBLIC
                | (meth.getModifiers() & ~(Modifier.PRIVATE
                                           | Modifier.PROTECTED
                                           | Modifier.ABSTRACT
                                           | Modifier.NATIVE
                                           | Modifier.SYNCHRONIZED)));
        setThrows(delegator, cp, meth);
        Bytecode code = new Bytecode(cp, 0, 0);
        code.addAload(0);
        int s = addLoadParameters(code, meth.getParameterTypes(), 1);
        code.addInvokespecial(declClass.getName(), meth.getName(), desc);
        addReturn(code, meth.getReturnType());
        code.setMaxLocals(++s);
        delegator.setCodeAttribute(code.toCodeAttribute());
        return delegator;
    }

    /**
     * @param delegatorName     null if the original method is abstract.
     */
    private static MethodInfo makeForwarder(String thisClassName,
                    Method meth, String desc, ConstPool cp,
                    Class declClass, String delegatorName, int index) {
        MethodInfo forwarder = new MethodInfo(cp, meth.getName(), desc);
        forwarder.setAccessFlags(Modifier.FINAL
                    | (meth.getModifiers() & ~(Modifier.ABSTRACT
                                               | Modifier.NATIVE
                                               | Modifier.SYNCHRONIZED)));
        setThrows(forwarder, cp, meth);
        int args = Descriptor.paramSize(desc);
        Bytecode code = new Bytecode(cp, 0, args + 2);
        /*
         * if (methods[index * 2] == null) {
         *   methods[index * 2]
         *     = RuntimeSupport.findMethod(this, <overridden name>, <desc>);
         *   methods[index * 2 + 1]
         *     = RuntimeSupport.findMethod(this, <delegator name>, <desc>);
         *     or = null // the original method is abstract.
         * }
         * return ($r)handler.invoke(this, methods[index * 2],
         *                methods[index * 2 + 1], $args);
         */
        int origIndex = index * 2;
        int delIndex = index * 2 + 1;
        int arrayVar = args + 1;
        code.addGetstatic(thisClassName, HOLDER, HOLDER_TYPE);
        code.addAstore(arrayVar);
        code.addAload(arrayVar);
        code.addIconst(origIndex);
        code.addOpcode(Opcode.AALOAD);
        code.addOpcode(Opcode.IFNONNULL);
        int pc = code.currentPc();
        code.addIndex(0);

        callFindMethod(code, "findSuperMethod", arrayVar, origIndex, meth.getName(), desc);
        callFindMethod(code, "findMethod", arrayVar, delIndex, delegatorName, desc);

        code.write16bit(pc, code.currentPc() - pc + 1);
        code.addAload(0);
        code.addGetfield(thisClassName, HANDLER, HANDLER_TYPE);
        code.addAload(0);

        code.addAload(arrayVar);
        code.addIconst(origIndex);
        code.addOpcode(Opcode.AALOAD);

        code.addAload(arrayVar);
        code.addIconst(delIndex);
        code.addOpcode(Opcode.AALOAD);

        makeParameterList(code, meth.getParameterTypes());
        code.addInvokeinterface(MethodHandler.class.getName(), "invoke",
            "(Ljava/lang/Object;Ljava/lang/reflect/Method;Ljava/lang/reflect/Method;[Ljava/lang/Object;)Ljava/lang/Object;",
            5);
        Class retType = meth.getReturnType();
        addUnwrapper(code, retType);
        addReturn(code, retType);

        forwarder.setCodeAttribute(code.toCodeAttribute());
        return forwarder;
    }

    private static void setThrows(MethodInfo minfo, ConstPool cp, Method orig) {
        Class[] exceptions = orig.getExceptionTypes();
        setThrows(minfo, cp, exceptions);
    }

    private static void setThrows(MethodInfo minfo, ConstPool cp,
                                  Class[] exceptions) {
        if (exceptions.length == 0)
            return;

        String[] list = new String[exceptions.length];
        for (int i = 0; i < exceptions.length; i++)
            list[i] = exceptions[i].getName();

        ExceptionsAttribute ea = new ExceptionsAttribute(cp);
        ea.setExceptions(list);
        minfo.setExceptionsAttribute(ea);
    }

    private static int addLoadParameters(Bytecode code, Class[] params,
                                         int offset) {
        int stacksize = 0;
        int n = params.length;
        for (int i = 0; i < n; ++i)
            stacksize += addLoad(code, stacksize + offset, params[i]);

        return stacksize;
    }

    private static int addLoad(Bytecode code, int n, Class type) {
        if (type.isPrimitive()) {
            if (type == Long.TYPE) {
                code.addLload(n);
                return 2;
            }
            else if (type == Float.TYPE)
                code.addFload(n);
            else if (type == Double.TYPE) {
                code.addDload(n);
                return 2;
            }
            else
                code.addIload(n);
        }
        else
            code.addAload(n);

        return 1;
    }

    private static int addReturn(Bytecode code, Class type) {
        if (type.isPrimitive()) {
            if (type == Long.TYPE) {
                code.addOpcode(Opcode.LRETURN);
                return 2;
            }
            else if (type == Float.TYPE)
                code.addOpcode(Opcode.FRETURN);
            else if (type == Double.TYPE) {
                code.addOpcode(Opcode.DRETURN);
                return 2;
            }
            else if (type == Void.TYPE) {
                code.addOpcode(Opcode.RETURN);
                return 0;
            }
            else
                code.addOpcode(Opcode.IRETURN);
        }
        else
            code.addOpcode(Opcode.ARETURN);

        return 1;
    }

    private static void makeParameterList(Bytecode code, Class[] params) {
        int regno = 1;
        int n = params.length;
        code.addIconst(n);
        code.addAnewarray("java/lang/Object");
        for (int i = 0; i < n; i++) {
            code.addOpcode(Opcode.DUP);
            code.addIconst(i);
            Class type = params[i];
            if (type.isPrimitive())
                regno = makeWrapper(code, type, regno);
            else {
                code.addAload(regno);
                regno++;
            }

            code.addOpcode(Opcode.AASTORE);
        }
    }

    private static int makeWrapper(Bytecode code, Class type, int regno) {
        int index = FactoryHelper.typeIndex(type);
        String wrapper = FactoryHelper.wrapperTypes[index]; 
        code.addNew(wrapper);
        code.addOpcode(Opcode.DUP);
        addLoad(code, regno, type);
        code.addInvokespecial(wrapper, "<init>",
                              FactoryHelper.wrapperDesc[index]);
        return regno + FactoryHelper.dataSize[index];
    }

    /**
     * @param methodName        might be null.
     */
    private static void callFindMethod(Bytecode code, String findMethod,
            int arrayVar, int index, String methodName, String desc) {
        String findClass = RuntimeSupport.class.getName();
        String findDesc
            = "(Ljava/lang/Object;Ljava/lang/String;Ljava/lang/String;)Ljava/lang/reflect/Method;";

        code.addAload(arrayVar);
        code.addIconst(index);
        if (methodName == null)
            code.addOpcode(Opcode.ACONST_NULL);
        else {
            code.addAload(0);
            code.addLdc(methodName);
            code.addLdc(desc);
            code.addInvokestatic(findClass, findMethod, findDesc);
        }

        code.addOpcode(Opcode.AASTORE);
    }

    private static void addUnwrapper(Bytecode code, Class type) {
        if (type.isPrimitive()) {
            if (type == Void.TYPE)
                code.addOpcode(Opcode.POP);
            else {
                int index = FactoryHelper.typeIndex(type);
                String wrapper = FactoryHelper.wrapperTypes[index];
                code.addCheckcast(wrapper);
                code.addInvokevirtual(wrapper,
                                      FactoryHelper.unwarpMethods[index],
                                      FactoryHelper.unwrapDesc[index]);
            }
        }
        else
            code.addCheckcast(type.getName());
    }

    private static MethodInfo makeWriteReplace(ConstPool cp) {
        MethodInfo minfo = new MethodInfo(cp, "writeReplace", "()Ljava/lang/Object;");
        String[] list = new String[1];
        list[0] = "java.io.ObjectStreamException";
        ExceptionsAttribute ea = new ExceptionsAttribute(cp);
        ea.setExceptions(list);
        minfo.setExceptionsAttribute(ea);
        Bytecode code = new Bytecode(cp, 0, 1);
        code.addAload(0);
        code.addInvokestatic("javassist.util.proxy.RuntimeSupport",
                             "makeSerializedProxy",
                             "(Ljava/lang/Object;)Ljavassist/util/proxy/SerializedProxy;");
        code.addOpcode(Opcode.ARETURN);
        minfo.setCodeAttribute(code.toCodeAttribute());
        return minfo;
    }
}