图片加载类源码httpcomponents-client-4.5.1

【核心代码】

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 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
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package org.apache.http.examples.client;

import java.io.IOException;
import java.util.concurrent.CancellationException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

import org.apache.http.HttpResponse;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.ResponseHandler;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.protocol.HttpClientContext;
import org.apache.http.concurrent.FutureCallback;
import org.apache.http.impl.client.FutureRequestExecutionService;
import org.apache.http.impl.client.HttpClientBuilder;
import org.apache.http.impl.client.HttpRequestFutureTask;

public class ClientWithRequestFuture {

    public static void main(String[] args) throws Exception {
        // the simplest way to create a HttpAsyncClientWithFuture
        HttpClient httpclient = HttpClientBuilder.create()
                .setMaxConnPerRoute(5)
                .setMaxConnTotal(5).build();
        ExecutorService execService = Executors.newFixedThreadPool(5);
        FutureRequestExecutionService requestExecService = new FutureRequestExecutionService(
                httpclient, execService);
        try {
            // Because things are asynchronous, you must provide a ResponseHandler
            ResponseHandler<Boolean> handler = new ResponseHandler<Boolean>() {
                @Override
                public Boolean handleResponse(HttpResponse response) throws ClientProtocolException, IOException {
                    // simply return true if the status was OK
                    return response.getStatusLine().getStatusCode() == 200;
                }
            };

            // Simple request ...
            HttpGet request1 = new HttpGet("http://httpbin.org/get");
            HttpRequestFutureTask<Boolean> futureTask1 = requestExecService.execute(request1,
                    HttpClientContext.create(), handler);
            Boolean wasItOk1 = futureTask1.get();
            System.out.println("It was ok? "    wasItOk1);

            // Cancel a request
            try {
                HttpGet request2 = new HttpGet("http://httpbin.org/get");
                HttpRequestFutureTask<Boolean> futureTask2 = requestExecService.execute(request2,
                        HttpClientContext.create(), handler);
                futureTask2.cancel(true);
                Boolean wasItOk2 = futureTask2.get();
                System.out.println("It was cancelled so it should never print this: "   wasItOk2);
            } catch (CancellationException e) {
                System.out.println("We cancelled it, so this is expected");
            }

            // Request with a timeout
            HttpGet request3 = new HttpGet("http://httpbin.org/get");
            HttpRequestFutureTask<Boolean> futureTask3 = requestExecService.execute(request3,
                    HttpClientContext.create(), handler);
            Boolean wasItOk3 = futureTask3.get(10, TimeUnit.SECONDS);
            System.out.println("It was ok? "    wasItOk3);

            FutureCallback<Boolean> callback = new FutureCallback<Boolean>() {
                @Override
                public void completed(Boolean result) {
                    System.out.println("completed with "   result);
                }

                @Override
                public void failed(Exception ex) {
                    System.out.println("failed with "   ex.getMessage());
                }

                @Override
                public void cancelled() {
                    System.out.println("cancelled");
                }
            };

            // Simple request with a callback
            HttpGet request4 = new HttpGet("http://httpbin.org/get");
            // using a null HttpContext here since it is optional
            // the callback will be called when the task completes, fails, or is cancelled
            HttpRequestFutureTask<Boolean> futureTask4 = requestExecService.execute(request4,
                    HttpClientContext.create(), handler, callback);
            Boolean wasItOk4 = futureTask4.get(10, TimeUnit.SECONDS);
            System.out.println("It was ok? "    wasItOk4);
        } finally {
            requestExecService.close();
        }
    }
}