libraries/invocation-cache/src/main/java/org/qi4j/library/invocationcache/ReturnCachedValueOnExceptionConcern.java

/*
 * Copyright 2007 Rickard Öberg.
 *
 * Licensed  under the  Apache License,  Version 2.0  (the "License");
 * you may not use  this file  except in  compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed  under the  License is distributed on an "AS IS" BASIS,
 * WITHOUT  WARRANTIES OR CONDITIONS  OF ANY KIND, either  express  or
 * implied.
 *
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.qi4j.library.invocationcache;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.util.Arrays;
import org.qi4j.api.common.AppliesTo;
import org.qi4j.api.concern.ConcernOf;
import org.qi4j.api.injection.scope.This;

/**
 * Return value of @Cached calls on exceptions.
 * <p>
 * If an Exception occurs, try to reuse a previous result. Don't do anything on Throwables.
 * </p>
 */
@AppliesTo( Cached.class )
public class ReturnCachedValueOnExceptionConcern
    extends ConcernOf<InvocationHandler>
    implements InvocationHandler
{
    @This
    private InvocationCache cache;

    @Override
    public Object invoke( Object proxy, Method method, Object[] args )
        throws Throwable
    {
        boolean voidReturnType = method.getReturnType().equals( Void.TYPE );
        if( cache != null || voidReturnType ) // Skip if void return type or no InvocationCache has been defined.
        {
            String cacheName = method.getName();
            if( args != null )
            {
                cacheName += Arrays.asList( args );
            }
            try
            {
                // Invoke method
                Object result = next.invoke( proxy, method, args );
                // update cache
                cache.setCachedValue( cacheName, result );
                return result;
            }
            catch( Exception e )
            {
                // Try cache
                return cache.cachedValue( cacheName );
            }
        }
        // if no InvocationCache is present.
        return next.invoke( proxy, method, args );
    }
}