本文将从代码的角度去引导如何使用httpclient的各个功能和特性。

第一个程序

import org.apache.commons.httpclient.*;
import org.apache.commons.httpclient.methods.*;
import org.apache.commons.httpclient.params.HttpMethodParams;

import java.io.*;

public class HttpClientTutorial {
  
  private static String url = "http://www.apache.org/";

  public static void main(String[] args) {
    // Create an instance of HttpClient.
    HttpClient client = new HttpClient();

    // Create a method instance.
    GetMethod method = new GetMethod(url);
    
    // Provide custom retry handler is necessary
    method.getParams().setParameter(HttpMethodParams.RETRY_HANDLER, 
    		new DefaultHttpMethodRetryHandler(3, false));

    try {
      // Execute the method.
      int statusCode = client.executeMethod(method);

      if (statusCode != HttpStatus.SC_OK) {
        System.err.println("Method failed: " + method.getStatusLine());
      }

      // Read the response body.
      byte[] responseBody = method.getResponseBody();

      // Deal with the response.
      // Use caution: ensure correct character encoding and is not binary data
      System.out.println(new String(responseBody));

    } catch (HttpException e) {
      System.err.println("Fatal protocol violation: " + e.getMessage());
      e.printStackTrace();
    } catch (IOException e) {
      System.err.println("Fatal transport error: " + e.getMessage());
      e.printStackTrace();
    } finally {
      // Release the connection.
      method.releaseConnection();
    }  
  }
}

模拟http网页登入

package org.apache.http.examples.client;

import java.net.URI;
import java.util.List;

import org.apache.http.HttpEntity;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpUriRequest;
import org.apache.http.client.methods.RequestBuilder;
import org.apache.http.cookie.Cookie;
import org.apache.http.impl.client.BasicCookieStore;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;

/**
 * A example that demonstrates how HttpClient APIs can be used to perform
 * form-based logon.
 */
public class ClientFormLogin {

    public static void main(String[] args) throws Exception {
        BasicCookieStore cookieStore = new BasicCookieStore();
        CloseableHttpClient httpclient = HttpClients.custom()
                .setDefaultCookieStore(cookieStore)
                .build();
        try {
            HttpGet httpget = new HttpGet("https://someportal/");
            CloseableHttpResponse response1 = httpclient.execute(httpget);
            try {
                HttpEntity entity = response1.getEntity();

                System.out.println("Login form get: " + response1.getStatusLine());
                EntityUtils.consume(entity);

                System.out.println("Initial set of cookies:");
                List<Cookie> cookies = cookieStore.getCookies();
                if (cookies.isEmpty()) {
                    System.out.println("None");
                } else {
                    for (int i = 0; i < cookies.size(); i++) {
                        System.out.println("- " + cookies.get(i).toString());
                    }
                }
            } finally {
                response1.close();
            }

            HttpUriRequest login = RequestBuilder.post()
                    .setUri(new URI("https://someportal/"))
                    .addParameter("IDToken1", "username")
                    .addParameter("IDToken2", "password")
                    .build();
            CloseableHttpResponse response2 = httpclient.execute(login);
            try {
                HttpEntity entity = response2.getEntity();

                System.out.println("Login form get: " + response2.getStatusLine());
                EntityUtils.consume(entity);

                System.out.println("Post logon cookies:");
                List<Cookie> cookies = cookieStore.getCookies();
                if (cookies.isEmpty()) {
                    System.out.println("None");
                } else {
                    for (int i = 0; i < cookies.size(); i++) {
                        System.out.println("- " + cookies.get(i).toString());
                    }
                }
            } finally {
                response2.close();
            }
        } finally {
            httpclient.close();
        }
    }
}

多表单Post示例

/**
 * Example how to use multipart/form encoded POST request.
 */
public class ClientMultipartFormPost {

    public static void main(String[] args) throws Exception {
        if (args.length != 1)  {
            System.out.println("File path not given");
            System.exit(1);
        }
        CloseableHttpClient httpclient = HttpClients.createDefault();
        try {
            HttpPost httppost = new HttpPost("http://localhost:8080" +
                    "/servlets-examples/servlet/RequestInfoExample");

            FileBody bin = new FileBody(new File(args[0]));
            StringBody comment = new StringBody("A binary file of some kind", ContentType.TEXT_PLAIN);

            HttpEntity reqEntity = MultipartEntityBuilder.create()
                    .addPart("bin", bin)
                    .addPart("comment", comment)
                    .build();


            httppost.setEntity(reqEntity);

            System.out.println("executing request " + httppost.getRequestLine());
            CloseableHttpResponse response = httpclient.execute(httppost);
            try {
                System.out.println("----------------------------------------");
                System.out.println(response.getStatusLine());
                HttpEntity resEntity = response.getEntity();
                if (resEntity != null) {
                    System.out.println("Response content length: " + resEntity.getContentLength());
                }
                EntityUtils.consume(resEntity);
            } finally {
                response.close();
            }
        } finally {
            httpclient.close();
        }
    }

}

用ResponseHandler来简化对http response的处理和资源释放

/**
 * This example demonstrates the use of the {@link ResponseHandler} to simplify
 * the process of processing the HTTP response and releasing associated resources.
 */
public class ClientWithResponseHandler {

    public final static void main(String[] args) throws Exception {
        CloseableHttpClient httpclient = HttpClients.createDefault();
        try {
            HttpGet httpget = new HttpGet("http://localhost/");

            System.out.println("Executing request " + httpget.getRequestLine());

            // Create a custom response handler
            ResponseHandler<String> responseHandler = new ResponseHandler<String>() {

                public String handleResponse(
                        final HttpResponse response) throws ClientProtocolException, IOException {
                    int status = response.getStatusLine().getStatusCode();
                    if (status >= 200 && status < 300) {
                        HttpEntity entity = response.getEntity();
                        return entity != null ? EntityUtils.toString(entity) : null;
                    } else {
                        throw new ClientProtocolException("Unexpected response status: " + status);
                    }
                }

            };
            String responseBody = httpclient.execute(httpget, responseHandler);
            System.out.println("----------------------------------------");
            System.out.println(responseBody);
        } finally {
            httpclient.close();
        }
    }

}

/**
 * An example that performs GETs from multiple threads.
 *
 */
public class ClientMultiThreadedExecution {

    public static void main(String[] args) throws Exception {
        // Create an HttpClient with the ThreadSafeClientConnManager.
        // This connection manager must be used if more than one thread will
        // be using the HttpClient.
        PoolingHttpClientConnectionManager cm = new PoolingHttpClientConnectionManager();
        cm.setMaxTotal(100);

        CloseableHttpClient httpclient = HttpClients.custom()
                .setConnectionManager(cm)
                .build();
        try {
            // create an array of URIs to perform GETs on
            String[] urisToGet = {
                "http://hc.apache.org/",
                "http://hc.apache.org/httpcomponents-core-ga/",
                "http://hc.apache.org/httpcomponents-client-ga/",
            };

            // create a thread for each URI
            GetThread[] threads = new GetThread[urisToGet.length];
            for (int i = 0; i < threads.length; i++) {
                HttpGet httpget = new HttpGet(urisToGet[i]);
                threads[i] = new GetThread(httpclient, httpget, i + 1);
            }

            // start the threads
            for (int j = 0; j < threads.length; j++) {
                threads[j].start();
            }

            // join the threads
            for (int j = 0; j < threads.length; j++) {
                threads[j].join();
            }

        } finally {
            httpclient.close();
        }
    }

    /**
     * A thread that performs a GET.
     */
    static class GetThread extends Thread {

        private final CloseableHttpClient httpClient;
        private final HttpContext context;
        private final HttpGet httpget;
        private final int id;

        public GetThread(CloseableHttpClient httpClient, HttpGet httpget, int id) {
            this.httpClient = httpClient;
            this.context = new BasicHttpContext();
            this.httpget = httpget;
            this.id = id;
        }

        /**
         * Executes the GetMethod and prints some status information.
         */
        @Override
        public void run() {
            try {
                System.out.println(id + " - about to get something from " + httpget.getURI());
                CloseableHttpResponse response = httpClient.execute(httpget, context);
                try {
                    System.out.println(id + " - get executed");
                    // get the response body as an array of bytes
                    HttpEntity entity = response.getEntity();
                    if (entity != null) {
                        byte[] bytes = EntityUtils.toByteArray(entity);
                        System.out.println(id + " - " + bytes.length + " bytes read");
                    }
                } finally {
                    response.close();
                }
            } catch (Exception e) {
                System.out.println(id + " - error: " + e);
            }
        }

    }

}

Java4Android之HttpClient入门使用代码集