用HttpURLConnection在服务器端发起HTTP Post请求的例子

通常情况下，http请求都是从浏览器端发起的，如提交一个表单，或点击一个链接，都会对服务器发送一个http请求。

但如果我们想在服务器发出一个http请求，如何才能做到呢，如果只是简单的http访问，java.net.URL就足够了，如：

URL url = new URL("http://www.baidu.com");

InputStream ins = url.openStream();

//通过这个InputStream对象就可拿到返回的HTML代码

 

 

但如果我们要从服务器对远程URL发出http post访问，并且要传递一些参数，甚至还要设置某些Cookie值，那就要

借助HttpURLConnection这个类了，我们可以用URL.openConnection()方法来得到这个类的对象，具体请看下例：

 

protected void doPost(HttpServletRequest request,

HttpServletResponse response) throws Exception {

 

HttpURLConnection httpConn = null;

try {

StringBuffer paramData = getQueryString(request);

String urlString = "http://localhost:8080/myweb/login.do";

 

URL url = new URL(urlString);

httpConn = (HttpURLConnection) url.openConnection();

httpConn.setDoInput(true);

httpConn.setDoOutput(true);

httpConn.setRequestMethod("POST");

httpConn.setRequestProperty("Content-Type",

"application/x-www-form-urlencoded");

String cookieString = getCookieString(request);

if (cookieString.length() > 0) // 往远程URL传递Cookie值

httpConn.setRequestProperty("Cookie", cookieString);

 

OutputStream os = httpConn.getOutputStream();

os.write(paramData.toString().getBytes()); // 往远程URL传递参数

os.flush();

os.close();

 

int code = httpConn.getResponseCode();

if (code == 200) { // 返回成功

BufferedReader reader = new BufferedReader(

new InputStreamReader(httpConn.getInputStream(), "utf-8"));

String line;

StringBuffer buffer = new StringBuffer();

while((line = reader.readLine()) != null) {

buffer.append(line).append("/n");

}

} else { // 访问失败

//forward error page

throw new Exception("Error occur when try to visit the url:" +

url.getPath() + " using HttpURLConnection");

}

} catch (Exception ex) {

throw new Exception("Error occur execute " +

"HttpRemoteProxy.performImpl(), the caused by " + ex);

} finally {

if (httpConn != null)

httpConn.disconnect();

}

}

 

/*

* 得到request所有的请求参数，并连接起来

*/

private StringBuffer getQueryString(HttpServletRequest request)

throws Exception {

 

Enumeration paramNames = request.getParameterNames();

StringBuffer paramData = new StringBuffer();

while (paramNames.hasMoreElements()) {

String name = (String)paramNames.nextElement();

String value = request.getParameter(name);

value = URLDecoder.decode(value, "utf-8");

paramData.append(name).append("=").append(value).append("&");

}

if (paramData.length() > 0) //delete the last char '&'

paramData.deleteCharAt(paramData.length() - 1);

return paramData;

}

 

/*

* 得到所有的cookie，并把它们连接起来

*/

private String getCookieString(HttpServletRequest request) throws Exception {

Cookie[] cookies = request.getCookies();

StringBuffer buffer = new StringBuffer();

for (int i = 0; i < cookies.length; i++) {

Cookie cookie = cookies[i];

String value = cookie.getValue();

String name = cookie.getName();

if (value != null && !value.equals(""))

buffer.append(name).append("=").append(value).append(";");

}

if (buffer.length() > 0)

buffer.deleteCharAt(buffer.length() - 1);//delete the last char ';'

return buffer.toString();

}

 

本文来自CSDN博客，转载请标明出处：http://blog.csdn.net/Linyufa/archive/2009/07/23/4373929.aspx