HttpClient基础教程 分类： C_OHTERS 2014-05-18 23:23 2600人阅读 评论(0) 收藏

1、HttpClient相关的重要资料

官方网站：http://hc.apache.org/

API：http://hc.apache.org/httpcomponents-client-4.3.x/httpclient/apidocs/index.html

tutorial: http://hc.apache.org/httpcomponents-client-4.3.x/tutorial/html/index.html 【PDF版本】http://hc.apache.org/httpcomponents-client-4.3.x/tutorial/pdf/httpclient-tutorial.pdf

2、HttpClient有2个版本

org.apache.http.impl.client.HttpClients 与 org.apache.commons.httpclient.HttpClient

目前后者已被废弃，apache已不再支持。

一般而言，使用HttpClient均需导入httpclient.jar与httpclient-core.jar2个包。

3、使用HttpClient进行网络处理的基本步骤

（1）通过get的方式获取到Response对象。

[java] view
plaincopy





CloseableHttpClient httpClient = HttpClients.createDefault();

HttpGet httpGet = new HttpGet("http://www.baidu.com/");

CloseableHttpResponse response = httpClient.execute(httpGet);

注意，必需要加上http://的前缀，否则会报：Target host is null异常。

（2）获取Response对象的Entity。

[java] view
plaincopy





HttpEntity entity = response.getEntity();

注：HttpClient将Response的正文及Request的POST/PUT方法中的正文均封装成一个HttpEntity对象。可以通过entity.getContenType()，entity.getContentLength()等方法获取到正文的相关信息。但最重要的方法是通过getContent()获取到InputStream对象。

（3）通过Entity获取到InputStream对象，然后对返回内容进行处理。

[java] view
plaincopy





is = entity.getContent();

sc = new Scanner(is);

// String filename = path.substring(path.lastIndexOf('/')+1);

String filename = "2.txt";

os = new PrintWriter(filename);

while (sc.hasNext()) {

os.write(sc.nextLine());

}

使用HtppClient下载一个网页的完整代码如下：

[java] view
plaincopy





package com.ljh.test;

import java.io.IOException;

import java.io.InputStream;

import java.io.PrintWriter;

import java.io.Writer;

import java.util.Scanner;

import org.apache.http.HttpEntity;

import org.apache.http.HttpStatus;

import org.apache.http.client.ClientProtocolException;

import org.apache.http.client.methods.CloseableHttpResponse;

import org.apache.http.client.methods.HttpGet;

import org.apache.http.impl.client.CloseableHttpClient;

import org.apache.http.impl.client.HttpClients;

public class DownloadWebPage{

public static void downloadPagebyGetMethod() throws IOException {

// 1、通过HttpGet获取到response对象

CloseableHttpClient httpClient = HttpClients.createDefault();

HttpGet httpGet = new HttpGet("http://www.baidu.com/");

CloseableHttpResponse response = httpClient.execute(httpGet);

InputStream is = null;

Scanner sc = null;

Writer os = null;

if (response.getStatusLine().getStatusCode() == HttpStatus.SC_OK) {

try {

// 2、获取response的entity。

HttpEntity entity = response.getEntity();

// 3、获取到InputStream对象，并对内容进行处理

is = entity.getContent();

sc = new Scanner(is);

// String filename = path.substring(path.lastIndexOf('/')+1);

String filename = "2.txt";

os = new PrintWriter(filename);

while (sc.hasNext()) {

os.write(sc.nextLine());

}

} catch (ClientProtocolException e) {

e.printStackTrace();

} finally {

if (sc != null) {

sc.close();

}

if (is != null) {

is.close();

}

if (os != null) {

os.close();

}

if (response != null) {

response.close();

}

}

}

}

public static void main(String[] args) {

try {

downloadPagebyGetMethod();

} catch (IOException e) {

e.printStackTrace();

}

}

}

注意：直接将HttpGet改为HttpPost，返回的结果有误，百度返回302状态，即重定向，新浪返回拒绝访问。怀疑大多网站均不允许POST方法直接访问网站。