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The AWS SDK for Java with support for OSGi. The AWS SDK for Java provides Java APIs for building software on AWS' cost-effective, scalable, and reliable infrastructure products. The AWS Java SDK allows developers to code against APIs for all of Amazon's infrastructure web services (Amazon S3, Amazon EC2, Amazon SQS, Amazon Relational Database Service, Amazon AutoScaling, etc).

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/*
 * Copyright 2015-2016 Amazon.com, Inc. or its affiliates. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License").
 * You may not use this file except in compliance with the License.
 * A copy of the License is located at
 *
 *  http://aws.amazon.com/apache2.0
 *
 * or in the "license" file accompanying this file. This file 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 com.amazonaws.handlers;

import java.util.List;
import java.util.Arrays;
import java.util.ArrayList;
import java.util.Collections;

import com.amazonaws.util.ValidationUtils;
import com.amazonaws.AmazonWebServiceRequest;
import com.amazonaws.Request;
import com.amazonaws.Response;
import com.amazonaws.annotation.ThreadSafe;
import com.amazonaws.http.HttpResponse;

/**
 * Composite {@link RequestHandler2} to execute a chain of {@link RequestHandler2} implementations
 * in stack order. That is if you have request handlers R1, R2, R3 the order of execution is as
 * follows
 * 
 *  *    
 * {@code   
 * R1.beforeMarshalling   
 * R2.beforeMarshalling   
 * R3.beforeMarshalling   
 *    
 * R1.beforeRequest   
 * R2.beforeRequest   
 * R3.beforeRequest   
 *    
 * R3.beforeUnmarshalling
 * R2.beforeUnmarshalling
 * R1.beforeUnmarshalling
 * 
 * R3.after(Response|Error)   
 * R2.after(Response|Error)   
 * R1.after(Response|Error)   
 * }
 * 
 */
@ThreadSafe
public class StackedRequestHandler implements IRequestHandler2 {

    private final List inOrderRequestHandlers;
    private final List reverseOrderRequestHandlers;

    public StackedRequestHandler(RequestHandler2...requestHandlers) {
       this(Arrays.asList(ValidationUtils.assertNotNull(requestHandlers, "requestHandlers")));
    }

    public StackedRequestHandler(List requestHandlers) {
        this.inOrderRequestHandlers = ValidationUtils.assertNotNull(requestHandlers, "requestHandlers");
        this.reverseOrderRequestHandlers = new ArrayList(requestHandlers);
        Collections.reverse(reverseOrderRequestHandlers);
    }

    @Override
    public AmazonWebServiceRequest beforeMarshalling(AmazonWebServiceRequest origRequest) {
        AmazonWebServiceRequest toReturn = origRequest;
        for (RequestHandler2 handler : inOrderRequestHandlers) {
            toReturn = handler.beforeMarshalling(toReturn);
        }
        return toReturn;
    }

    @Override
    public void beforeRequest(Request request) {
        for (RequestHandler2 handler : inOrderRequestHandlers) {
            handler.beforeRequest(request);
        }
    }

    @Override
    public HttpResponse beforeUnmarshalling(Request request, HttpResponse origHttpResponse) {
        HttpResponse toReturn = origHttpResponse;
        for(RequestHandler2 handler : reverseOrderRequestHandlers) {
            toReturn = handler.beforeUnmarshalling(request, toReturn);
        }
        return toReturn;
    }

    @Override
    public void afterResponse(Request request, Response response) {
        for(RequestHandler2 handler : reverseOrderRequestHandlers) {
            handler.afterResponse(request, response);
        }
    }

    @Override
    public void afterError(Request request, Response response, Exception e) {
        for(RequestHandler2 handler : reverseOrderRequestHandlers) {
            handler.afterError(request, response, e);
        }
    }

}