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Allows Java applications written for a servlet container to run in AWS Lambda

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/*
 * Copyright 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.serverless.proxy;

import java.io.IOException;
import java.io.OutputStream;

/**
 * Implementing sub-classes of this interface are used by container objects to handle exceptions. Normally, exceptions are
 * handled by the client applications directly within the container and a valid HTTP response is expected. This handler
 * is used for exceptions thrown by the library while marshalling and unmarshalling requests and responses.
 *
 * The interface declares two methods. A typed handle method for requests that are being proxied using a
 * request and response type LambdaContainerHandler, and a stream-based
 * handle method for 
 * Lambda's RequestStreamHandler.
 *
 * @see com.amazonaws.serverless.proxy.internal.LambdaContainerHandler
 *
 * @param  The type for the Lambda return value. Implementing sub-classes are required to return a valid
 *                      instance of the response type.
 */
public interface ExceptionHandler {
    /**
     * The handle method is called by the container object whenever an exception occurs in the proxy method
     * for typed calls
     * @param ex The exception thrown by the application
     * @return A valid response object
     */
    ResponseType handle(Throwable ex);

    /**
     * This handle implementation is called whenever an exception occurs in the stream-based proxy method.
     * @param ex The exception thrown by the application
     * @param stream The OutputStream where the exception will be written
     * @throws IOException When the exception handler fails to write to the OutputStream
     */
    void handle(Throwable ex, OutputStream stream)
            throws IOException;
}