HttpClient使用详解

Posted 2020-06-09

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HttpClient使用详解

标签： httpclient | 发表时间：2015-01-22 12:07 | 作者：fang323619

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出处：http://blog.csdn.net

HttpClient:是一个接口

首先需要先创建一个DefaultHttpClient的实例

HttpClient httpClient=new DefaultHttpClient();

发送GET请求:

先创建一个HttpGet对象,传入目标的网络地址,然后调用HttpClient的execute()方法即可:

HttpGet HttpGet=new HttpGet(“http://www.baidu.com”);

httpClient.execute(httpGet);

发送POST请求:

创建一个HttpPost对象,传入目标的网络地址:

HttpPost httpPost=new HttpPost(“http://www.baidu.com”);

通过一个NameValuePair集合来存放待提交的参数,并将这个参数集合传入到一个UrlEncodedFormEntity中,然后调用HttpPost的setEntity()方法将构建好的UrlEncodedFormEntity传入:

List<NameValuePair>params=newArrayList<NameValuePair>();

Params.add(new BasicNameValuePair(“username”,”admin”));

Params.add(new BasicNameValuePair(“password”,”123456”));

UrlEncodedFormEntity entity=newUrlEncodedFormEntity(params,”utf-8”);

httpPost.setEntity(entity);

调用HttpClient的execute()方法,并将HttpPost对象传入即可:

HttpClient.execute(HttpPost);

执行execute()方法之后会返回一个HttpResponse对象,服务器所返回的所有信息就保护在HttpResponse里面.

先取出服务器返回的状态码,如果等于200就说明请求和响应都成功了:

If(httpResponse.getStatusLine().getStatusCode()==200){

//请求和响应都成功了

HttpEntityentity=HttpResponse.getEntity();//调用getEntity()方法获取到一个HttpEntity实例

Stringresponse=EntityUtils.toString(entity,”utf-8”);//用 EntityUtils.toString()这个静态方法将HttpEntity转换成字符串,防止服务器返回的数据带有中文,所以在转换的时候将字符集指定成utf-8就可以了

}

Http协议的重要性相信不用我多说了，HttpClient相比传统JDK自带的URLConnection，增加了易用性和灵活性（具体区别，日后我们再讨论），它不仅是客户端发送Http请求变得容易，而且也方便了开发人员测试接口（基于Http协议的），即提高了开发的效率，也方便提高代码的健壮性。因此熟练掌握HttpClient是很重要的必修内容，掌握HttpClient后，相信对于Http协议的了解会更加深入。

一、简介

HttpClient是Apache Jakarta Common下的子项目，用来提供高效的、最新的、功能丰富的支持HTTP协议的客户端编程工具包，并且它支持HTTP协议最新的版本和建议。 HttpClient已经应用在很多的项目中，比如Apache Jakarta上很著名的另外两个开源项目Cactus和htmlUnit都使用了HttpClient。

下载地址: http://hc.apache.org/downloads.cgi

二、特性

1. 基于标准、纯净的java语言。实现了Http1.0和Http1.1

2. 以可扩展的面向对象的结构实现了Http全部的方法（GET, POST, PUT, DELETE, HEAD, OPTIONS, and TRACE）。

3. 支持HTTPS协议。

4. 通过Http代理建立透明的连接。

5. 利用CONNECT方法通过Http代理建立隧道的https连接。

6. Basic, Digest, NTLMv1, NTLMv2, NTLM2 Session, SNPNEGO/Kerberos认证方案。

7. 插件式的自定义认证方案。

8. 便携可靠的套接字工厂使它更容易的使用第三方解决方案。

9. 连接管理器支持多线程应用。支持设置最大连接数，同时支持设置每个主机的最大连接数，发现并关闭过期的连接。

10. 自动处理Set-Cookie中的Cookie。

11. 插件式的自定义Cookie策略。

12. Request的输出流可以避免流中内容直接缓冲到socket服务器。

13. Response的输入流可以有效的从socket服务器直接读取相应内容。

14. 在http1.0和http1.1中利用KeepAlive保持持久连接。

15. 直接获取服务器发送的response code和 headers。

16. 设置连接超时的能力。

17. 实验性的支持http1.1 response caching。

18. 源代码基于Apache License 可免费获取。

三、使用方法

使用HttpClient发送请求、接收响应很简单，一般需要如下几步即可。

1. 创建HttpClient对象。

2. 创建请求方法的实例，并指定请求URL。如果需要发送GET请求，创建HttpGet对象；如果需要发送POST请求，创建HttpPost对象。

3. 如果需要发送请求参数，可调用HttpGet、HttpPost共同的setParams(HetpParams params)方法来添加请求参数；对于HttpPost对象而言，也可调用setEntity(HttpEntity entity)方法来设置请求参数。

4. 调用HttpClient对象的execute(HttpUriRequest request)发送请求，该方法返回一个HttpResponse。

5. 调用HttpResponse的getAllHeaders()、getHeaders(String name)等方法可获取服务器的响应头；调用HttpResponse的getEntity()方法可获取HttpEntity对象，该对象包装了服务器的响应内容。程序可通过该对象获取服务器的响应内容。

6. 释放连接。无论执行方法是否成功，都必须释放连接

四、实例

[java] view plain copy

package com.test;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.security.KeyManagementException;
import java.security.KeyStore;
import java.security.KeyStoreException;
import java.security.NoSuchAlgorithmException;
import java.security.cert.CertificateException;
import java.util.ArrayList;
import java.util.List;
import javax.net.ssl.SSLContext;
import org.apache.http.HttpEntity;
import org.apache.http.NameValuePair;
import org.apache.http.ParseException;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.conn.ssl.SSLConnectionSocketFactory;
import org.apache.http.conn.ssl.SSLContexts;
import org.apache.http.conn.ssl.TrustSelfSignedStrategy;
import org.apache.http.entity.ContentType;
import org.apache.http.entity.mime.MultipartEntityBuilder;
import org.apache.http.entity.mime.content.FileBody;
import org.apache.http.entity.mime.content.StringBody;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.message.BasicNameValuePair;
import org.apache.http.util.EntityUtils;
import org.junit.Test;
public class HttpClientTest {
@Test
public void jUnitTest() {
get();
}
/**
* HttpClient连接SSL
*/
public void ssl() {
CloseableHttpClient httpclient = null;
try {
KeyStore trustStore = KeyStore.getInstance(KeyStore.getDefaultType());
FileInputStream instream = new FileInputStream(new File("d:\\tomcat.keystore"));
try {
// 加载keyStore d:\\tomcat.keystore
trustStore.load(instream, "123456".toCharArray());
} catch (CertificateException e) {
e.printStackTrace();
} finally {
try {
instream.close();
} catch (Exception ignore) {
}
}
// 相信自己的CA和所有自签名的证书
SSLContext sslcontext = SSLContexts.custom().loadTrustMaterial(trustStore, new TrustSelfSignedStrategy()).build();
// 只允许使用TLSv1协议
SSLConnectionSocketFactory sslsf = new SSLConnectionSocketFactory(sslcontext, new String[] { "TLSv1" }, null,
SSLConnectionSocketFactory.BROWSER_COMPATIBLE_HOSTNAME_VERIFIER);
httpclient = HttpClients.custom().setSSLSocketFactory(sslsf).build();
// 创建http请求(get方式)
HttpGet httpget = new HttpGet("https://localhost:8443/myDemo/Ajax/serivceJ.action");
System.out.println("executing request" + httpget.getRequestLine());
CloseableHttpResponse response = httpclient.execute(httpget);
try {
HttpEntity entity = response.getEntity();
System.out.println("----------------------------------------");
System.out.println(response.getStatusLine());
if (entity != null) {
System.out.println("Response content length: " + entity.getContentLength());
System.out.println(EntityUtils.toString(entity));
EntityUtils.consume(entity);
}
} finally {
response.close();
}
} catch (ParseException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (KeyManagementException e) {
e.printStackTrace();
} catch (NoSuchAlgorithmException e) {
e.printStackTrace();
} catch (KeyStoreException e) {
e.printStackTrace();
} finally {
if (httpclient != null) {
try {
httpclient.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
/**
* post方式提交表单（模拟用户登录请求）
*/
public void postForm() {
// 创建默认的httpClient实例.
CloseableHttpClient httpclient = HttpClients.createDefault();
// 创建httppost
HttpPost httppost = new HttpPost("http://localhost:8080/myDemo/Ajax/serivceJ.action");
// 创建参数队列
List<namevaluepair> formparams = new ArrayList<namevaluepair>();
formparams.add(new BasicNameValuePair("username", "admin"));
formparams.add(new BasicNameValuePair("password", "123456"));
UrlEncodedFormEntity uefEntity;
try {
uefEntity = new UrlEncodedFormEntity(formparams, "UTF-8");
httppost.setEntity(uefEntity);
System.out.println("executing request " + httppost.getURI());
CloseableHttpResponse response = httpclient.execute(httppost);
try {
HttpEntity entity = response.getEntity();
if (entity != null) {
System.out.println("--------------------------------------");
System.out.println("Response content: " + EntityUtils.toString(entity, "UTF-8"));
System.out.println("--------------------------------------");
}
} finally {
response.close();
}
} catch (ClientProtocolException e) {
e.printStackTrace();
} catch (UnsupportedEncodingException e1) {
e1.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
// 关闭连接,释放资源
try {
httpclient.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
/**
* 发送 post请求访问本地应用并根据传递参数不同返回不同结果
*/
public void post() {
// 创建默认的httpClient实例.
CloseableHttpClient httpclient = HttpClients.createDefault();
// 创建httppost
HttpPost httppost = new HttpPost("http://localhost:8080/myDemo/Ajax/serivceJ.action");
// 创建参数队列
List<namevaluepair> formparams = new ArrayList<namevaluepair>();
formparams.add(new BasicNameValuePair("type", "house"));
UrlEncodedFormEntity uefEntity;
try {
uefEntity = new UrlEncodedFormEntity(formparams, "UTF-8");
httppost.setEntity(uefEntity);
System.out.println("executing request " + httppost.getURI());
CloseableHttpResponse response = httpclient.execute(httppost);
try {
HttpEntity entity = response.getEntity();
if (entity != null) {
System.out.println("--------------------------------------");
System.out.println("Response content: " + EntityUtils.toString(entity, "UTF-8"));
System.out.println("--------------------------------------");
}
} finally {
response.close();
}
} catch (ClientProtocolException e) {
e.printStackTrace();
} catch (UnsupportedEncodingException e1) {
e1.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
// 关闭连接,释放资源
try {
httpclient.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
/**
* 发送 get请求
*/
public void get() {
CloseableHttpClient httpclient = HttpClients.createDefault();
try {
// 创建httpget.
HttpGet httpget = new HttpGet("http://www.baidu.com/");
System.out.println("executing request " + httpget.getURI());
// 执行get请求.
CloseableHttpResponse response = httpclient.execute(httpget);
try {
// 获取响应实体
HttpEntity entity = response.getEntity();
System.out.println("--------------------------------------");
// 打印响应状态
System.out.println(response.getStatusLine());
if (entity != null) {
// 打印响应内容长度
System.out.println("Response content length: " + entity.getContentLength());
// 打印响应内容
System.out.println("Response content: " + EntityUtils.toString(entity));
}
System.out.println("------------------------------------");
} finally {
response.close();
}
} catch (ClientProtocolException e) {
e.printStackTrace();
} catch (ParseException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
// 关闭连接,释放资源
try {
httpclient.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
/**
* 上传文件
*/
public void upload() {
CloseableHttpClient httpclient = HttpClients.createDefault();
try {
HttpPost httppost = new HttpPost("http://localhost:8080/myDemo/Ajax/serivceFile.action");
FileBody bin = new FileBody(new File("F:\\image\\sendpix0.jpg"));
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();
}
} catch (ClientProtocolException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
httpclient.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
package com.jia.networktest;

import java.io.BufferedReader;
import java.io.DataOutputStream;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.HttpClient;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.message.BasicNameValuePair;
import org.apache.http.util.EntityUtils;

import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;

public class MainActivity extends Activity implements OnClickListener {

public static final int SHOW_RESPONSE = 0;
public static final int SHOW_HTTPCLIENT = 1;
private Button send_request;
private TextView responseText;
private Button btn_httpClient;
private Handler handler = new Handler() {
public void handleMessage(Message msg) {
switch (msg.what) {
case SHOW_RESPONSE:
String response = (String) msg.obj;
// 在这里进行UI操作,将结果显示到界面上
responseText.setText(response);
case SHOW_HTTPCLIENT:
String m_httpClient = (String) msg.obj;
// 在这里进行UI操作,将结果显示到界面上
responseText.setText(m_httpClient);
}
}
};

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
send_request = (Button) findViewById(R.id.send_request);
responseText = (TextView) findViewById(R.id.response);
btn_httpClient = (Button) findViewById(R.id.HttpClient);
send_request.setOnClickListener(this);
btn_httpClient.setOnClickListener(this);
}

@Override
public void onClick(View v) {
if (v.getId() == R.id.send_request) {
sendRequestWithHttpURLConnection();
} else if (v.getId() == R.id.HttpClient) {
sendRequestWithHttpClient();
}

}

private void sendRequestWithHttpClient() {
new Thread(new Runnable() {

@Override
public void run() {
try {
HttpClient httpClient = new DefaultHttpClient();
HttpPost httpPost = new HttpPost("http://www.baidu.com");
List<NameValuePair> params = new ArrayList<NameValuePair>();
params.add(new BasicNameValuePair("username",
"[email protected]"));
params.add(new BasicNameValuePair("password", "yaowentian"));
UrlEncodedFormEntity urlEncodedFormEntity = new UrlEncodedFormEntity(
params, "utf-8");
httpPost.setEntity(urlEncodedFormEntity);

HttpResponse httpResponse = httpClient.execute(httpPost);
if (httpResponse.getStatusLine().getStatusCode() == 200) {
// 请求和响应都成功了
HttpEntity entity = httpResponse.getEntity();// 获取到一个HttpEntity实例
String response = EntityUtils.toString(entity, "utf-8");// 用EntityUtils.toString()这个方法将HttpEntity转换成字符串
Message message = new Message();
message.what = SHOW_HTTPCLIENT;
// 将服务器返回的结果存放到Message中
message.obj = response.toString();
handler.sendMessage(message);
}
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}

}
}).start();

}

private void sendRequestWithHttpURLConnection() {
// 开启线程来发起网络请求
new Thread(new Runnable() {

@Override
public void run() {
HttpURLConnection connection = null;
try {
URL url = new URL("http://www.baidu.com");
connection = (HttpURLConnection) url.openConnection();
connection.setRequestMethod("POST");
connection.setConnectTimeout(8000);
connection.setReadTimeout(8000);
DataOutputStream out = new DataOutputStream(connection
.getOutputStream());
out.writeBytes("[email protected]&password=yaowentian");
InputStream in = connection.getInputStream();
// 下面对获取到的输入流进行读取
BufferedReader reader = new BufferedReader(
new InputStreamReader(in));
StringBuilder response = new StringBuilder();
String line;
while ((line = reader.readLine()) != null) {
response.append(line);
}
Message message = new Message();
message.what = SHOW_RESPONSE;
// 将服务器返回的结果存放到message中
message.obj = response.toString();
handler.sendMessage(message);
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
} finally {
if (connection != null) {
connection.disconnect();
}
}

}
}).start();
}
}

首先要注意的有以下几点：
1、httpclient连接后资源释放问题很重要，就跟我们用database connection要释放资源一样。
2、https网站采用ssl加密传输，证书导入要注意。
3、做这样的项目最好先了解下http协义，比如302,301,200,404返回代码的含义（这是最基本的）,cookie,session的机制。
4、httpclient的redirect状态默认是自动的，这在很大程度上给开发者很大的方便（如一些授权获得cookie），但是有时要手动管理下，比如
　　有时会遇到CircularRedirectException异常，出现这样的情况是因为返回的头文件中location值指向之前重复(端口号可以不同)地址，导致可能会出现死
循环递归重定向，这时可以手动关闭:method.setFollowRedirects(false)
5、有的网站会先判别用户的请求是否是来自浏览器，如不是，则返回不正确的文本，所以用httpclient抓取信息时在头部加入如下信息：
header.put("User-Agent", "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; QQDownload 1.7; .NET CLR 1.1.4322; CIBA; .NET CLR 2.0.50727)");
6、当post请求提交数据时要改变默认编码，不然的话提交上去的数据会出现乱码。重写postMethod的setContentCharSet()方法就可以了：

下面写一个通用类来处理request请求返回的文本:

Java代码

/*
* HttpRequestProxy.java
*
* Created on November 3, 2008, 9:53 AM
*/
package cn.com.mozat.net;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
import org.apache.commons.httpclient.Header;
import org.apache.commons.httpclient.HttpClient;
import org.apache.commons.httpclient.HttpException;
import org.apache.commons.httpclient.HttpMethod;
import org.apache.commons.httpclient.NameValuePair;
import org.apache.commons.httpclient.SimpleHttpConnectionManager;
import org.apache.commons.httpclient.methods.GetMethod;
import org.apache.commons.httpclient.methods.PostMethod;
import cn.com.mozat.exception.CustomException;
/**
*
* @author bird email:[email protected]
*
* 2008-11-4 09:49:48
*/
public class HttpRequestProxy{
//超时间隔
private static int connectTimeOut = 60000;
//让connectionmanager管理httpclientconnection时是否关闭连接
private static boolean alwaysClose = false;
//返回数据编码格式
private String encoding = "UTF-8";
private final HttpClient client = new HttpClient(new SimpleHttpConnectionManager(alwaysClose));
public HttpClient getHttpClient(){
return client;
}
/**
* 用法：
* HttpRequestProxy hrp = new HttpRequestProxy();
* hrp.doRequest("http://www.163.com",null,null,"gbk");
*
* @param url 请求的资源ＵＲＬ
* @param postData POST请求时form表单封装的数据没有时传null
* @param header request请求时附带的头信息(header) 没有时传null
* @param encoding response返回的信息编码格式没有时传null
* @return response返回的文本数据
* @throws CustomException
*/
public String doRequest(String url,Map postData,Map header,String encoding) throws CustomException{
String responseString = null;
//头部请求信息
Header[] headers = null;
if(header != null){
Set entrySet = header.entrySet();
int dataLength = entrySet.size();
headers= new Header[dataLength];
int i = 0;
for(Iterator itor = entrySet.iterator();itor.hasNext();){
Map.Entry entry = (Map.Entry)itor.next();
headers[i++] = new Header(entry.getKey().toString(),entry.getValue().toString());
}
}
//post方式
if(postData!=null){
PostMethod postRequest = new PostMethod(url.trim());
if(headers != null){
for(int i = 0;i < headers.length;i++){
postRequest.setRequestHeader(headers[i]);
}
}
Set entrySet = postData.entrySet();
int dataLength = entrySet.size();
NameValuePair[] params = new NameValuePair[dataLength];
int i = 0;
for(Iterator itor = entrySet.iterator();itor.hasNext();){
Map.Entry entry = (Map.Entry)itor.next();
params[i++] = new NameValuePair(entry.getKey().toString(),entry.getValue().toString());
}
postRequest.setRequestBody(params);
try {
responseString = this.executeMethod(postRequest,encoding);
} catch (CustomException e) {
throw e;
} finally{
postRequest.releaseConnection();
}
}
//get方式
if(postData == null){
GetMethod getRequest = new GetMethod(url.trim());
if(headers != null){
for(int i = 0;i < headers.length;i++){
getRequest.setRequestHeader(headers[i]);
}
}
try {
responseString = this.executeMethod(getRequest,encoding);
} catch (CustomException e) {
e.printStackTrace();
throw e;
}finally{
getRequest.releaseConnection();
}
}
return responseString;
}
private String executeMethod(HttpMethod request, String encoding) throws CustomException{
String responseContent = null;
InputStream responseStream = null;
BufferedReader rd = null;
try {
this.getHttpClient().executeMethod(request);
if(encoding != null){
responseStream = request.getResponseBodyAsStream();
rd = new BufferedReader(new InputStreamReader(responseStream,
encoding));
String tempLine = rd.readLine();
StringBuffer tempStr = new StringBuffer();
String crlf=System.getProperty("line.separator");
while (tempLine != null)
{
tempStr.append(tempLine);
tempStr.append(crlf);
tempLine = rd.readLine();
}
responseContent = tempStr.toString();
}else
responseContent = request.getResponseBodyAsString();
Header locationHeader = request.getResponseHeader("location");
//返回代码为302,301时，表示页面己经重定向，则重新请求location的url，这在
//一些登录授权取cookie时很重要
if (locationHeader != null) {
String redirectUrl = locationHeader.getValue();
this.doRequest(redirectUrl, null, null,null);
}
} catch (HttpException e) {
throw new CustomException(e.getMessage());
} catch (IOException e) {
throw new CustomException(e.getMessage());
} finally{
if(rd != null)
try {
rd.close();
} catch (IOException e) {
throw new CustomException(e.getMessage());
}
if(responseStream != null)
try {
responseStream.close();
} catch (IOException e) {
throw new CustomException(e.getMessage());
}
}
return responseContent;
}
/**
* 特殊请求数据,这样的请求往往会出现redirect本身而出现递归死循环重定向
* 所以单独写成一个请求方法
* 比如现在请求的url为：http://localhost:8080/demo/index.jsp
* 返回代码为302 头部信息中location值为:http://localhost:8083/demo/index.jsp
* 这时httpclient认为进入递归死循环重定向，抛出CircularRedirectException异常
* @param url
* @return
* @throws CustomException
*/
public String doSpecialRequest(String url,int count,String encoding) throws CustomException{
String str = null;
InputStream responseStream = null;
BufferedReader rd = null;
GetMethod getRequest = new GetMethod(url);
//关闭httpclient自动重定向动能
getRequest.setFollowRedirects(false);
try {
this.client.executeMethod(getRequest);
Header header = getRequest.getResponseHeader("location");
if(header!= null){
//请求重定向后的ＵＲＬ，count同时加1
this.doSpecialRequest(header.getValue(),count+1, encoding);
}
//这里用count作为标志位，当count为0时才返回请求的ＵＲＬ文本,
//这样就可以忽略所有的递归重定向时返回文本流操作，提高性能

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