001// Copyright 2009, 2010, 2011 The Apache Software Foundation
002//
003// Licensed under the Apache License, Version 2.0 (the "License");
004// you may not use this file except in compliance with the License.
005// You may obtain a copy of the License at
006//
007// http://www.apache.org/licenses/LICENSE-2.0
008//
009// Unless required by applicable law or agreed to in writing, software
010// distributed under the License is distributed on an "AS IS" BASIS,
011// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
012// See the License for the specific language governing permissions and
013// limitations under the License.
014
015package org.apache.tapestry5.ioc.internal.services;
016
017import org.apache.tapestry5.commons.ObjectCreator;
018import org.apache.tapestry5.ioc.MethodAdviceReceiver;
019import org.apache.tapestry5.ioc.annotations.NotLazy;
020import org.apache.tapestry5.ioc.annotations.PreventServiceDecoration;
021import org.apache.tapestry5.ioc.internal.util.InternalUtils;
022import org.apache.tapestry5.ioc.services.LazyAdvisor;
023import org.apache.tapestry5.ioc.services.ThunkCreator;
024import org.apache.tapestry5.plastic.MethodAdvice;
025import org.apache.tapestry5.plastic.MethodInvocation;
026
027import java.lang.reflect.Method;
028
029@PreventServiceDecoration
030public class LazyAdvisorImpl implements LazyAdvisor
031{
032    private final ThunkCreator thunkCreator;
033
034    public LazyAdvisorImpl(ThunkCreator thunkCreator)
035    {
036        this.thunkCreator = thunkCreator;
037    }
038
039    @Override
040    public void addLazyMethodInvocationAdvice(MethodAdviceReceiver methodAdviceReceiver)
041    {
042        for (Method m : methodAdviceReceiver.getInterface().getMethods())
043        {
044            if (filter(m))
045                addAdvice(m, methodAdviceReceiver);
046        }
047    }
048
049    private void addAdvice(Method method, MethodAdviceReceiver receiver)
050    {
051        final Class thunkType = method.getReturnType();
052
053        final String description = String.format("<%s Thunk for %s>", thunkType.getName(),
054                InternalUtils.asString(method));
055
056        MethodAdvice advice = new MethodAdvice()
057        {
058            /**
059             * When the method is invoked, we don't immediately proceed. Instead, we return a thunk instance
060             * that defers its behavior to the lazily invoked invocation.
061             */
062            @Override
063            public void advise(final MethodInvocation invocation)
064            {
065                ObjectCreator deferred = new ObjectCreator()
066                {
067                    @Override
068                    public Object createObject()
069                    {
070                        invocation.proceed();
071
072                        return invocation.getReturnValue();
073                    }
074                };
075
076                ObjectCreator cachingObjectCreator = new CachingObjectCreator(deferred);
077
078                Object thunk = thunkCreator.createThunk(thunkType, cachingObjectCreator, description);
079
080                invocation.setReturnValue(thunk);
081            }
082        };
083
084        receiver.adviseMethod(method, advice);
085    }
086
087    private boolean filter(Method method)
088    {
089        if (method.getAnnotation(NotLazy.class) != null)
090            return false;
091
092        if (!method.getReturnType().isInterface())
093            return false;
094
095        for (Class extype : method.getExceptionTypes())
096        {
097            if (!RuntimeException.class.isAssignableFrom(extype))
098                return false;
099        }
100
101        return true;
102    }
103}