HTTP协议是目前互联网上最重要的协议，许多软件与服务都需要依赖HTTP协议。
虽然java.net这个package中包含了对HTTP的基本支持，但还有很多高级和复杂的功能无法实现，这不能不说是一个遗憾。
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HttpClient作为Apache的开源项目项目之一，为基于HTTP协议的操作提供了强大的客户端执行支持，最新的版本为3.0RC3。
下面通过一个例子简要展示HttpClient的使用方法：
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
iimport java.io.UnsupportedEncodingException;
import java.util.*;
import org.apache.commons.httpclient.Header;
import org.apache.commons.httpclient.HostConfiguration;
import org.apache.commons.httpclient.HttpClient;
import org.apache.commons.httpclient.HttpConnection;
import org.apache.commons.httpclient.MultiThreadedHttpConnectionManager;
import org.apache.commons.httpclient.NameValuePair;
import org.apache.commons.httpclient.methods.GetMethod;
import org.apache.commons.httpclient.methods.PostMethod;
/**
* @author steven
*/
public class HttpClientExample {
//获得ConnectionManager，设置相关参数
private static MultiThreadedHttpConnectionManager manager =
new MultiThreadedHttpConnectionManager();
private static int connectionTimeOut = 20000;
private static int socketTimeOut = 10000;
private static int maxConnectionPerHost = 5;
private static int maxTotalConnections = 40;
//标志初始化是否完成的flag
private static boolean initialed = false;
//初始化ConnectionManger的方法
public static void SetPara() {
manager.getParams().setConnectionTimeout(connectionTimeOut);
manager.getParams().setSoTimeout(socketTimeOut);
manager.getParams()
.setDefaultMaxConnectionsPerHost(maxConnectionPerHost);
manager.getParams().setMaxTotalConnections(maxTotalConnections);
initialed = true;
}
//通过get方法获取网页内容
public static String getGetResponseWithHttpClient(String url, String encode) {
HttpClient client = new HttpClient(manager);
if (initialed) {
HttpClientExample.SetPara();
}
GetMethod get = new GetMethod(url);
get.setFollowRedirects(true);
String result = null;
StringBuffer resultBuffer = new StringBuffer();
try {
client.executeMethod(get);
//在目标页面情况未知的条件下，不推荐使用getResponseBodyAsString()方法
//String strGetResponseBody = post.getResponseBodyAsString();
BufferedReader in = new BufferedReader(
new InputStreamReader(
get.getResponseBodyAsStream(),
get.getResponseCharSet()));
String inputLine = null;
while ((inputLine = in.readLine()) != null) {
resultBuffer.append(inputLine);
resultBuffer.append("\n");
}
in.close();
result = resultBuffer.toString();
//iso-8859-1 is the default reading encode
result = HttpClientExample.ConverterStringCode(resultBuffer.toString(),
get.getResponseCharSet(),
encode);
} catch (Exception e) {
e.printStackTrace();
result = "";
} finally {
get.releaseConnection();
return result;
}
}
public static String getPostResponseWithHttpClient(String url,
String encode) {
HttpClient client = new HttpClient(manager);
if (initialed) {
HttpClientExample.SetPara();
}
PostMethod post = new PostMethod(url);
post.setFollowRedirects(false);
StringBuffer resultBuffer = new StringBuffer();
String result = null;
try {
client.executeMethod(post);
BufferedReader in = new BufferedReader(
new InputStreamReader(
post.getResponseBodyAsStream(),
post.getResponseCharSet()));
String inputLine = null;
while ((inputLine = in.readLine()) != null) {
resultBuffer.append(inputLine);
resultBuffer.append("\n");
}
in.close();
//iso-8859-1 is the default reading encode
result = HttpClientExample.ConverterStringCode(resultBuffer.toString(),
post.getResponseCharSet(),
encode);
} catch (Exception e) {
e.printStackTrace();
result = "";
} finally {
post.releaseConnection();
return result;
}
}
public static String getPostResponseWithHttpClient(String url,
String encode,
NameValuePair[] nameValuePair) {
HttpClient client = new HttpClient(manager);
if (initialed) {
HttpClientExample.SetPara();
}
PostMethod post = new PostMethod(url);
post.setRequestBody(nameValuePair);
post.setFollowRedirects(false);
String result = null;
StringBuffer resultBuffer = new StringBuffer();
try {
client.executeMethod(post);
BufferedReader in = new BufferedReader(
new InputStreamReader(
post.getResponseBodyAsStream(),
post.getResponseCharSet()));
String inputLine = null;
while ((inputLine = in.readLine()) != null) {
resultBuffer.append(inputLine);
resultBuffer.append("\n");
}
in.close();
//iso-8859-1 is the default reading encode
result = HttpClientExample.ConverterStringCode(resultBuffer.toString(),
post.getResponseCharSet(),
encode);
} catch (Exception e) {
e.printStackTrace();
result = "";
} finally {
post.releaseConnection();
return result;
}
}
private static String ConverterStringCode(String source, String srcEncode, String destEncode) {
if (src != null) {
try {
return new String(src.getBytes(srcEncode), destEncode);
} catch (UnsupportedEncodingException e) {
// TODO Auto-generated catch block
e.printStackTrace();
return "";
}
} else {
return "";
}
}
}
之后，就可以通过下面的代码获得目标网页：
String source = HttpClientExample.getGetResponseWithHttpClient("www.sina.com.cn", "GBK");
注意，在默认情况下，HttpClient的Request的Head中
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User-Agent的值是Jakarta Commons-HttpClient 3.0RC1，如果需要改变它（例如，变为Mozilla/4.0），必须在调用之前运行如下语句：
System.getProperties().setProperty("httpclient.useragent", "Mozilla/4.0");
来自:http://www.cnjm.net/tech/article1153.html
posted on 2009-06-23 17:56
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