HttpClient 4.1.3 初学篇---使用Get和Post模拟登录简单页面（分别带参数）
最近需要解决的问题需要用到Httpclient，模拟登陆网站！成功之后就可以用代码的方式获取网站内容或者发送请求，类似网络爬虫。
但是在网上找了好多篇Blog，发现每一片的写法都不一样，也纠结了些时间，很纳闷，才发现Httpclient版本不一样。。。现在在这里说明我使用的版本是HttpClient 4.1.3，我已上传下载
看了些Blog，发现直接访问大型的网站不太容易，于是就自己写了小的站点，只有一个Servlet，来接受参数(用户名和密码)就ok了！
这个Servlet就只有get与post方法，而且方法一样，如下
<span style="font-family:Microsoft YaHei;font-size:14px;">public class LoginServlet extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html");
PrintWriter out = response.getWriter();
String name = request.getParameter("name");
String psd = request.getParameter("pwd");
if("wang".equals(name)&&"123".equals(psd)){
out.print("true");
}else{
out.print("false");
}
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
this.doGet(request, response);
}
</span>
简单的“服务器”就搭建好了，接下来就是在客户端使用Httpclient模拟登录了！
先分析一下想要成功的登录进去的Url是：http://localhost:8080/HttpServer/LoginServlet?name=wang&pwd=123
参数就是两个("name","wang")和("pwd","123");
接下来就是HttpClent登场了！！！
- 创建client
<span style="font-family:Microsoft YaHei;font-size:14px;">HttpClient client = new DefaultHttpClient();</span>
- 选择发送请求的方式
<span style="font-family:Microsoft YaHei;font-size:14px;">HttpPost httpPost = new HttpPost(url); //发送请求的方法，此处为Post HttpGet httpGet = new HttpGet(url); //发送请求的方法，此处为Get</span>
- 设置参数，Post和Get添加参数的方式不同，下面代码有给出
- 发送请求
<span style="font-family:Microsoft YaHei;font-size:14px;"> HttpResponse response = client.execute(httpPost); </span>服务器收到请求做出的响应和相关Html内容都在response里，就看怎么使用了！
下面是代码
<span style="font-family:Microsoft YaHei;font-size:14px;">private static void PostMethd() throws UnsupportedEncodingException,
IOException, ClientProtocolException {
HttpClient client = new DefaultHttpClient(); //创建clent
HttpPost httpPost = new HttpPost(url); //发送请求的方法，此处为Post
List<NameValuePair> formparams = new ArrayList<NameValuePair>(); //Post方式添加参数的方法
formparams.add(new BasicNameValuePair("name",name));
formparams.add(new BasicNameValuePair("pwd", pwd));
UrlEncodedFormEntity uefEntity;
uefEntity = new UrlEncodedFormEntity(formparams, "UTF-8"); //防止出现乱码，加上UTF-8
httpPost.setEntity(uefEntity);
HttpResponse response = client.execute(httpPost); //提交请求
InputStream in = PringStatus(response);
in.close(); //关闭输出流
client.getConnectionManager().shutdown(); //关闭client
}
private static void GetMethd() throws UnsupportedEncodingException,
IOException, ClientProtocolException {
HttpClient client = new DefaultHttpClient();
StringBuilder sb = new StringBuilder(url); //此处是Get请求，添加参数的方法有点复杂，但我没有找到好的方法，
sb.append("?"); //还请看官拍砖
sb.append("name=").append(name);
sb.append("&&");
sb.append("pwd=").append(pwd);
HttpGet httpGet = new HttpGet(sb.toString());
HttpResponse response = client.execute(httpGet);
InputStream in = PringStatus(response);
in.close();
client.getConnectionManager().shutdown();
}
private static InputStream PringStatus(HttpResponse response)
throws IOException, UnsupportedEncodingException {
System.out.println(response.getStatusLine().toString()); //请求发送之后，服务器响应的状态
InputStream in = response.getEntity().getContent();
BufferedReader br = new BufferedReader
(new InputStreamReader(in,"utf-8"));
String line = null;
while((line = br.readLine())!=null){
System.out.println(line.toString());
}
return in;
}</span>
好，打开tomcat，跑起来验证一下是否成功！
<span style="font-family:Microsoft YaHei;font-size:14px;">HTTP/1.1 200 OK true </span>第一个行是服务器响应的状态，第二行则是html内容，因为servlet里的是
<span style="font-family:Microsoft YaHei;font-size:14px;">out.print("true");</span>
到这里，HttpClient模拟登录简单的网站就完成了，接下来我会继续学习使用HttpClient登录网站，并保留cookie，发送请求并解析等相关内容！
代码下载