com.amazonaws.handlers.HandlerChainFactory Maven / Gradle / Ivy

Go to download

Show more of this group Show more artifacts with this name
Show all versions of aws-java-sdk Show documentation

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).

The newest version!

/*
 * 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.handlers;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.List;

import com.amazonaws.AmazonClientException;
import com.amazonaws.util.ClassLoaderHelper;

/**
 * Factory for creating request/response handler chains.
 */
public class HandlerChainFactory {

    /**
     * For backward compatibility, constructs a new request handler chain
     * adapted to {@link RequestHandler2} by analyzing the specified classpath
     * resource.
     * 
     * @param resource
     *            The resource to load from the classpath containing the list of
     *            request handlers to instantiate.
     * 
     * @return A list of request handlers based on the handlers referenced in
     *         the specified resource.
     */
    public List newRequestHandlerChain(String resource) {
        return createRequestHandlerChain(resource, RequestHandler.class);
    }

    /**
     * Constructs a new request handler (v2) chain by analyzing the specified
     * classpath resource.
     *
     * @param resource
     *            The resource to load from the classpath containing the list of
     *            request handlers to instantiate.
     *
     * @return A list of request handlers based on the handlers referenced in
     *         the specified resource.
     */
    public List newRequestHandler2Chain(String resource) {
        return createRequestHandlerChain(resource, RequestHandler2.class);
    }

    private List createRequestHandlerChain(String resource, Class handlerApiClass) {
        List handlers = new ArrayList();
        BufferedReader reader = null;

        try {
            InputStream input = getClass().getResourceAsStream(resource);
            if (input == null) return handlers;

            reader = new BufferedReader(new InputStreamReader(input));
            while (true) {
                String requestHandlerClassName = reader.readLine();
                if (requestHandlerClassName == null)
                    break;
                requestHandlerClassName = requestHandlerClassName.trim();
                if (requestHandlerClassName.equals("")) 
                    continue;
                Class requestHandlerClass = ClassLoaderHelper.loadClass(
                    requestHandlerClassName,
                    handlerApiClass, getClass());
                Object requestHandlerObject = requestHandlerClass.newInstance();
                if (handlerApiClass.isInstance(requestHandlerObject)) {
                    if (handlerApiClass == RequestHandler2.class) {
                        RequestHandler2 h = (RequestHandler2)requestHandlerObject;
                        handlers.add(h);
                    } else if (handlerApiClass == RequestHandler.class) {
                        RequestHandler h = (RequestHandler)requestHandlerObject;
                        handlers.add(RequestHandler2.adapt(h));
                    } else {
                        throw new IllegalStateException();
                    }
                } else {
                    throw new AmazonClientException(
                        "Unable to instantiate request handler chain for client.  "
                                + "Listed request handler ('"
                                + requestHandlerClassName + "') "
                                + "does not implement the "
                                + handlerApiClass + " API.");
                }
            }
        } catch (Exception e) {
            throw new AmazonClientException("Unable to instantiate request handler chain for client: "
                    + e.getMessage(), e);
        } finally {
            try {
                if (reader != null) {
                    reader.close();
                }
            } catch (IOException e) {
            }
        }
        return handlers;
    }
}