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The Amazon Web Services 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 2010-2014 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.http;

import java.util.List;

import org.w3c.dom.Document;
import org.w3c.dom.Node;
import org.xml.sax.SAXParseException;

import com.amazonaws.AmazonClientException;
import com.amazonaws.AmazonServiceException;
import com.amazonaws.transform.Unmarshaller;
import com.amazonaws.util.XpathUtils;

/**
 * Implementation of HttpResponseHandler that handles only error responses from
 * Amazon Web Services. A list of unmarshallers is passed into the constructor,
 * and while handling a response, each unmarshaller is tried, in order, until
 * one is found that can successfully unmarshall the error response.  If no
 * unmarshaller is found that can unmarshall the error response, a generic
 * AmazonServiceException is created and populated with the AWS error response
 * information (error message, AWS error code, AWS request ID, etc).
 */
public class DefaultErrorResponseHandler
        implements HttpResponseHandler {

    /**
     * The list of error response unmarshallers to try to apply to error
     * responses.
     */
    private List> unmarshallerList;

    /**
     * Constructs a new DefaultErrorResponseHandler that will handle error
     * responses from Amazon services using the specified list of unmarshallers.
     * Each unmarshaller will be tried, in order, until one is found that can
     * unmarshall the error response.
     *
     * @param unmarshallerList
     *            The list of unmarshallers to try using when handling an error
     *            response.
     */
    public DefaultErrorResponseHandler(
            List> unmarshallerList) {
        this.unmarshallerList = unmarshallerList;
    }

    /* (non-Javadoc)
     * @see com.amazonaws.http.HttpResponseHandler#handle(com.amazonaws.http.HttpResponse)
     */
    public AmazonServiceException handle(HttpResponse errorResponse)
            throws Exception {
        Document document;
        try {
            document = XpathUtils.documentFrom(errorResponse.getContent());
        } catch (SAXParseException e) {
            AmazonServiceException exception =
                new AmazonServiceException(String.format("Unable to unmarshall error response (%s)", e.getMessage()), e);
            exception.setErrorCode(String.format("%s %s", errorResponse.getStatusCode(), errorResponse.getStatusText()));
            exception.setErrorType(AmazonServiceException.ErrorType.Unknown);
            exception.setStatusCode(errorResponse.getStatusCode());

            return exception;
        }

        /*
         * We need to select which exception unmarshaller is the correct one to
         * use from all the possible exceptions this operation can throw.
         * Currently we rely on the unmarshallers to return null if they can't
         * unmarshall the response, but we might need something a little more
         * sophisticated in the future.
         */
        for (Unmarshaller unmarshaller : unmarshallerList) {
            AmazonServiceException ase = unmarshaller.unmarshall(document);
            if (ase != null) {
                ase.setStatusCode(errorResponse.getStatusCode());
                return ase;
            }
        }

        throw new AmazonClientException("Unable to unmarshall error response from service");
    }

    /**
     * Since this response handler completely consumes all the data from the
     * underlying HTTP connection during the handle method, we don't need to
     * keep the HTTP connection open.
     *
     * @see com.amazonaws.http.HttpResponseHandler#needsConnectionLeftOpen()
     */
    public boolean needsConnectionLeftOpen() {
        return false;
    }

}