javassist/src/main/javassist/util/proxy/ProxyFactory.java

/*
 * Javassist, a Java-bytecode translator toolkit.
 * Copyright (C) 1999-2006 Shigeru Chiba. All Rights Reserved.
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (the "License"); you may not use this file except in compliance with
 * the License.  Alternatively, the contents of this file may be used under
 * the terms of the GNU Lesser General Public License Version 2.1 or later.
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 */

package javassist.util.proxy;

import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Constructor;
import java.lang.reflect.Member;
import java.lang.reflect.Modifier;
import java.security.ProtectionDomain;
import java.util.HashMap;
import java.util.WeakHashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
import java.lang.ref.WeakReference;

import javassist.CannotCompileException;
import javassist.bytecode.*;

/**
 * Factory of dynamic proxy classes.
 *
 * <p>This factory generates a class that extends the given super class and implements
 * the given interfaces.  The calls of the methods inherited from the super class are
 * forwarded and then <code>invoke()</code> is called on the method handler
 * associated with the generated class.  The calls of the methods from the interfaces
 * are also forwarded to the method handler.
 *
 * <p>For example, if the following code is executed,
 * 
 * <ul><pre>
 * ProxyFactory f = new ProxyFactory();
 * f.setSuperclass(Foo.class);
 * MethodHandler mi = new MethodHandler() {
 *     public Object invoke(Object self, Method m, Method proceed,
 *                          Object[] args) throws Throwable {
 *         System.out.println("Name: " + m.getName());
 *         return proceed.invoke(self, args);  // execute the original method.
 *     }
 * };
 * f.setHandler(mi);
 * f.setFilter(new MethodFilter() {
 *     public boolean isHandled(Method m) {
 *         // ignore finalize()
 *         return !m.getName().equals("finalize");
 *     }
 * });
 * Class c = f.createClass();
 * Foo foo = (Foo)c.newInstance();
 * </pre></ul>
 *
 * <p>Then, the following method call will be forwarded to MethodHandler
 * <code>mi</code> and prints a message before executing the originally called method
 * <code>bar()</code> in <code>Foo</code>.
 *
 * <ul><pre>
 * foo.bar();
 * </pre></ul>
 *
 * <p>To change the method handler during runtime,
 * execute the following code:
 *
 * <ul><pre>
 * MethodHandler mi2 = ... ;    // another handler
 * ((ProxyObject)foo).setHandler(mi2);
 * </pre></ul>
 *
 * <p>Here is an example of method handler.  It does not execute
 * anything except invoking the original method:
 *
 * <ul><pre>
 * class SimpleHandler implements MethodHandler {
 *     public Object invoke(Object self, Method m,
 *                          Method proceed, Object[] args) throws Exception {
 *         return proceed.invoke(self, args);
 *     }
 * }
 * </pre></ul>
 *
 * @see MethodHandler
 * @since 3.1
 */
public class ProxyFactory {
    private Class superClass;
    private Class[] interfaces;
    private MethodFilter methodFilter;
    private MethodHandler handler;
    private Class thisClass;

    /**
     * If the value of this variable is not null, the class file of
     * the generated proxy class is written under the directory specified
     * by this variable.  For example, if the value is 
     * <code>"."</code>, then the class file is written under the current
     * directory.  This method is for debugging.
     *
     * <p>The default value is null.
     */
    public String writeDirectory;

    private static final Class OBJECT_TYPE = Object.class;

    private static final String HOLDER = "_methods_";
    private static final String HOLDER_TYPE = "[Ljava/lang/reflect/Method;";
    private static final String HANDLER = "handler";
    private static final String NULL_INTERCEPTOR_HOLDER = "javassist.util.proxy.RuntimeSupport";
    private static final String DEFAULT_INTERCEPTOR = "default_interceptor";
    private static final String HANDLER_TYPE
        = 'L' + MethodHandler.class.getName().replace('.', '/') + ';';
    private static final String HANDLER_SETTER = "setHandler";
    private static final String HANDLER_SETTER_TYPE = "(" + HANDLER_TYPE + ")V";

    /**
     * If true, a generated proxy class is cached and it will be reused
     * when generating the proxy class with the same properties is requested.
     * The default value is true.
     *
     * @since 3.4
     */
    public static boolean useCache = true; 

    private static WeakHashMap proxyCache = new WeakHashMap();

    static class CacheKey {
        private String classes;
        private MethodFilter filter;
        private int hash;
        WeakReference proxyClass;

        public CacheKey(Class superClass, Class[] interfaces, MethodFilter f) {
            classes = getKey(superClass, interfaces);
            hash = classes.hashCode();
            filter = f;
            proxyClass = null;
        }

        public int hashCode() { return hash; }

        public boolean equals(Object obj) {
            if (obj instanceof CacheKey) {
                CacheKey target = (CacheKey)obj;
                return target.filter == filter && target.classes.equals(classes);
            }
            else
                return false;
        }

        static String getKey(Class superClass, Class[] interfaces) {
            StringBuffer sbuf = new StringBuffer();
            if (superClass != null)
                sbuf.append(superClass.getName());
            sbuf.append(':');
            if (interfaces != null) {
                int len = interfaces.length;
                for (int i = 0; i < len; i++)
                    sbuf.append(interfaces[i].getName()).append(',');
            }

            return sbuf.toString();
        }
    }

    /**
     * Constructs a factory of proxy class.
     */
    public ProxyFactory() {
        superClass = null;
        interfaces = null;
        methodFilter = null;
        handler = null;
        thisClass = null;
        writeDirectory = null;
    }

    /**
     * Sets the super class of a proxy class.
     */
    public void setSuperclass(Class clazz) {
        superClass = clazz;
    }

    /**
     * Obtains the super class set by <code>setSuperclass()</code>.
     *
     * @since 3.4
     */
    public Class getSuperclass() { return superClass; }

    /**
     * Sets the interfaces of a proxy class.
     */
    public void setInterfaces(Class[] ifs) {
        interfaces = ifs;
    }

    /**
     * Obtains the interfaces set by <code>setInterfaces</code>.
     *
     * @since 3.4
     */
    public Class[] getInterfaces() { return interfaces; }

    /**
     * Sets a filter that selects the methods that will be controlled by a handler.
     */
    public void setFilter(MethodFilter mf) {
        methodFilter = mf;
    }

    /**
     * Generates a proxy class.
     */
    public Class createClass() {
        if (thisClass == null) {
            ClassLoader cl = getClassLoader();
            if (useCache)
                createClass2(cl);
            else
                createClass3(cl);
        }

        return thisClass;
    }

    private void createClass2(ClassLoader cl) {
        CacheKey key = new CacheKey(superClass, interfaces, methodFilter);
        synchronized (proxyCache) {
            HashMap cacheForTheLoader = (HashMap)proxyCache.get(cl);
            if (cacheForTheLoader == null) {
                cacheForTheLoader = new HashMap();
                proxyCache.put(cl, cacheForTheLoader);
                cacheForTheLoader.put(key, key);
            }
            else {
                CacheKey found = (CacheKey)cacheForTheLoader.get(key);
                if (found == null)
                    cacheForTheLoader.put(key, key);
                else {
                    key = found;
                    Class c = isValidEntry(key);    // no need to synchronize
                    if (c != null) {
                        thisClass = c;
                        return;
                    }
                }
            }
        }

        synchronized (key) {
            Class c = isValidEntry(key);
            if (c == null) {
                createClass3(cl);
                key.proxyClass = new WeakReference(thisClass);
            }
            else
                thisClass = c; 
        }
    }

    private Class isValidEntry(CacheKey key) {
        WeakReference ref = key.proxyClass;
        if (ref != null) {
            Class c = (Class)ref.get();
            if(c != null && getHandler(c) == handler)
                return c;
        }

        return null;
    }

    private void createClass3(ClassLoader cl) {
        try {
            ClassFile cf = make();
            if (writeDirectory != null)
                FactoryHelper.writeFile(cf, writeDirectory);

            thisClass = FactoryHelper.toClass(cf, cl, getDomain());
            setHandler();
        }
        catch (CannotCompileException e) {
            throw new RuntimeException(e.getMessage(), e);
        }

    }

    /**
     * A provider of class loaders.
     *
     * @see #classLoaderProvider
     * @since 3.4
     */
    public static interface ClassLoaderProvider {
        /**
         * Returns a class loader.
         *
         * @param pf    a proxy factory that is going to obtain a class loader.
         */
        public ClassLoader get(ProxyFactory pf);
    }

    /**
     * A provider used by <code>createClass()</code> for obtaining
     * a class loader.
     * <code>get()</code> on this <code>ClassLoaderProvider</code> object
     * is called to obtain a class loader.
     *
     * <p>The value of this field can be updated for changing the default
     * implementation.
     *
     * <p>Example:
     * <ul><pre>
     * ProxyFactory.classLoaderProvider = new ProxyFactory.ClassLoaderProvider() {
     *     public ClassLoader get(ProxyFactory pf) {
     *         return Thread.currentThread().getContextClassLoader();
     *     }
     * };
     * </pre></ul>
     *
     * @since 3.4
     */
    public static ClassLoaderProvider classLoaderProvider
        = new ClassLoaderProvider() {
              public ClassLoader get(ProxyFactory pf) {
                  return pf.getClassLoader0();
              }
          };

    protected ClassLoader getClassLoader() {
        return classLoaderProvider.get(this);
    }

    protected ClassLoader getClassLoader0() {
        ClassLoader loader = null;
        if (superClass != null && !superClass.getName().equals("java.lang.Object"))
            loader = superClass.getClassLoader();
        else if (interfaces != null && interfaces.length > 0)
            loader = interfaces[0].getClassLoader();
 
        if (loader == null) {
            loader = getClass().getClassLoader();
            // In case javassist is in the endorsed dir
            if (loader == null) {
                loader = Thread.currentThread().getContextClassLoader();
                if (loader == null)
                    loader = ClassLoader.getSystemClassLoader();
            }
        }

        return loader;
    }

    protected ProtectionDomain getDomain() {
        Class clazz;
        if (superClass != null && !superClass.getName().equals("java.lang.Object"))
            clazz = superClass;
        else if (interfaces != null && interfaces.length > 0)
            clazz = interfaces[0];
        else
            clazz = this.getClass();

        return clazz.getProtectionDomain();
    }

    /**
     * Creates a proxy class and returns an instance of that class.
     *
     * @param paramTypes    parameter types for a constructor.
     * @param args          arguments passed to a constructor.
     */
    public Object create(Class[] paramTypes, Object[] args)
        throws NoSuchMethodException, IllegalArgumentException,
               InstantiationException, IllegalAccessException, InvocationTargetException
    {
        Class c = createClass();
        Constructor cons = c.getConstructor(paramTypes);
        return cons.newInstance(args);
    }

    /**
     * Sets the default invocation handler.  This invocation handler is shared
     * among all the instances of a proxy class unless another is explicitly
     * specified.
     */
    public void setHandler(MethodHandler mi) {
        handler = mi;
        setHandler();
    }

    private void setHandler() {
        if (thisClass != null && handler != null)
            try {
                Field f = thisClass.getField(DEFAULT_INTERCEPTOR);
                f.setAccessible(true);
                f.set(null, handler);
                f.setAccessible(false);
            }
            catch (Exception e) {
                throw new RuntimeException(e);
            }
    }

    static MethodHandler getHandler(Class clazz) {
        try {
            Field f = clazz.getField(DEFAULT_INTERCEPTOR);
            f.setAccessible(true);
            MethodHandler h = (MethodHandler)f.get(null);
            f.setAccessible(false);
            return h;
        }
        catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    private static int counter = 0;

    private static synchronized String makeProxyName(String classname) {
        return classname + "_$$_javassist_" + counter++;
    }

    private ClassFile make() throws CannotCompileException {
        String superName, classname;
        if (interfaces == null)
            interfaces = new Class[0];

        if (superClass == null) {
            superClass = OBJECT_TYPE;
            superName = superClass.getName();
            classname = interfaces.length == 0 ? superName
                                               : interfaces[0].getName(); 
        }
        else {
            superName = superClass.getName();
            classname = superName;
        }

        if (Modifier.isFinal(superClass.getModifiers()))
            throw new CannotCompileException(superName + " is final");

        classname = makeProxyName(classname);
        if (classname.startsWith("java."))
            classname = "org.javassist.tmp." + classname;

        ClassFile cf = new ClassFile(false, classname, superName);
        cf.setAccessFlags(AccessFlag.PUBLIC);
        setInterfaces(cf, interfaces);
        ConstPool pool = cf.getConstPool();
        FieldInfo finfo = new FieldInfo(pool, DEFAULT_INTERCEPTOR, HANDLER_TYPE);
        finfo.setAccessFlags(AccessFlag.PUBLIC | AccessFlag.STATIC);
        cf.addField(finfo);

        FieldInfo finfo2 = new FieldInfo(pool, HANDLER, HANDLER_TYPE);
        finfo2.setAccessFlags(AccessFlag.PRIVATE);
        cf.addField(finfo2);

        HashMap allMethods = getMethods(superClass, interfaces);
        int size = allMethods.size();
        makeConstructors(classname, cf, pool, classname);
        int s = overrideMethods(cf, pool, classname, allMethods);
        addMethodsHolder(cf, pool, classname, s);
        addSetter(classname, cf, pool);

        thisClass = null;          
        return cf;
    }

    private static void setInterfaces(ClassFile cf, Class[] interfaces) {
        String setterIntf = ProxyObject.class.getName();
        String[] list;
        if (interfaces == null || interfaces.length == 0)
            list = new String[] { setterIntf };
        else {
            list = new String[interfaces.length + 1];
            for (int i = 0; i < interfaces.length; i++)
                list[i] = interfaces[i].getName();

            list[interfaces.length] = setterIntf;
        }

        cf.setInterfaces(list);
    }

    private static void addMethodsHolder(ClassFile cf, ConstPool cp,
                                         String classname, int size)
        throws CannotCompileException
    {
        FieldInfo finfo = new FieldInfo(cp, HOLDER, HOLDER_TYPE);
        finfo.setAccessFlags(AccessFlag.PRIVATE | AccessFlag.STATIC);
        cf.addField(finfo);
        MethodInfo minfo = new MethodInfo(cp, "<clinit>", "()V");
        Bytecode code = new Bytecode(cp, 0, 0);
        code.addIconst(size * 2);
        code.addAnewarray("java.lang.reflect.Method");
        code.addPutstatic(classname, HOLDER, HOLDER_TYPE);
        code.addOpcode(Bytecode.RETURN);
        minfo.setCodeAttribute(code.toCodeAttribute());
        cf.addMethod(minfo);
    }

    private static void addSetter(String classname, ClassFile cf, ConstPool cp)
        throws CannotCompileException
    {
        MethodInfo minfo = new MethodInfo(cp, HANDLER_SETTER,
                                          HANDLER_SETTER_TYPE);
        minfo.setAccessFlags(AccessFlag.PUBLIC);
        Bytecode code = new Bytecode(cp, 2, 2);
        code.addAload(0);
        code.addAload(1);
        code.addPutfield(classname, HANDLER, HANDLER_TYPE);
        code.addOpcode(Bytecode.RETURN);
        minfo.setCodeAttribute(code.toCodeAttribute());
        cf.addMethod(minfo);
    }

    private int overrideMethods(ClassFile cf, ConstPool cp, String className,
                                HashMap allMethods)
        throws CannotCompileException
    {
        String prefix = makeUniqueName("_d", allMethods);
        Set entries = allMethods.entrySet();
        Iterator it = entries.iterator();
        int index = 0;
        while (it.hasNext()) {
            Map.Entry e = (Map.Entry)it.next();
            String key = (String)e.getKey();
            Method meth = (Method)e.getValue();
            int mod = meth.getModifiers();
            if (!Modifier.isFinal(mod) && !Modifier.isStatic(mod)
                    && isVisible(mod, className, meth))
                if (methodFilter == null || methodFilter.isHandled(meth))
                    override(className, meth, prefix, index++,
                             keyToDesc(key), cf, cp);
        }

        return index;
    }

    private void override(String thisClassname, Method meth, String prefix,
                          int index, String desc, ClassFile cf, ConstPool cp)
        throws CannotCompileException
    {
        Class declClass = meth.getDeclaringClass();
        String delegatorName = prefix + index + meth.getName();
        if (Modifier.isAbstract(meth.getModifiers()))
            delegatorName = null;
        else {
            MethodInfo delegator
                = makeDelegator(meth, desc, cp, declClass, delegatorName);
            // delegator is not a bridge method.  See Sec. 15.12.4.5 of JLS 3rd Ed.
            delegator.setAccessFlags(delegator.getAccessFlags() & ~AccessFlag.BRIDGE);
            cf.addMethod(delegator);
        }

        MethodInfo forwarder
            = makeForwarder(thisClassname, meth, desc, cp, declClass,
                            delegatorName, index);
        cf.addMethod(forwarder);
    }

    private void makeConstructors(String thisClassName, ClassFile cf,
            ConstPool cp, String classname) throws CannotCompileException
    {
        Constructor[] cons = superClass.getDeclaredConstructors();
        for (int i = 0; i < cons.length; i++) {
            Constructor c = cons[i];
            int mod = c.getModifiers();
            if (!Modifier.isFinal(mod) && !Modifier.isPrivate(mod)
                    && isVisible(mod, classname, c)) {
                MethodInfo m = makeConstructor(thisClassName, c, cp, superClass);
                cf.addMethod(m);
            }
        }
    }

    private static String makeUniqueName(String name, HashMap hash) {
        Set keys = hash.keySet();
        if (makeUniqueName0(name, keys.iterator()))
            return name;

        for (int i = 100; i < 999; i++) {
            String s = name + i;
            if (makeUniqueName0(s, keys.iterator()))
                return s;
        }

        throw new RuntimeException("cannot make a unique method name");
    }

    private static boolean makeUniqueName0(String name, Iterator it) {
        while (it.hasNext()) {
            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());
    }
}