java 发送http请求（提交form表单）

 
写一个servlet用于测试请求

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class Abc extends HttpServlet {

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
System.out.println("doGet");
this.doPost(request, response);
}

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
System.out.println("doPost");
System.out.println("aaa : "+request.getParameter("aaa"));
System.out.println("param1 : "+request.getParameter("param1"));

System.out.println(request.getHeader("avc"));

PrintWriter pw = response.getWriter();
pw.write(request.getParameter("param1"));
pw.flush();
pw.close();
}

}

 
web.xml配置文件

<servlet>
<description></description>
<display-name>Abc</display-name>
<servlet-name>Abc</servlet-name>
<servlet-class>com.Abc</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>Abc</servlet-name>
<url-pattern>/Abc</url-pattern>
</servlet-mapping>

 
抽象出一个工具请求类

package http;

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.Map;
import java.util.Map.Entry;

public class HttpUtil {

public static String http(String url, Map<String, String> params) {
URL u = null;
HttpURLConnection con = null;
// 构建请求参数
StringBuffer sb = new StringBuffer();
if (params != null) {
for (Entry<String, String> e : params.entrySet()) {
sb.append(e.getKey());
sb.append("=");
sb.append(e.getValue());
sb.append("&");
}
sb.substring(0, sb.length() - 1);
}
System.out.println("send_url:" + url);
System.out.println("send_data:" + sb.toString());
// 尝试发送请求
try {
u = new URL(url);
con = (HttpURLConnection) u.openConnection();
//// POST 只能为大写，严格限制，post会不识别
con.setRequestMethod("POST");
con.setDoOutput(true);
con.setDoInput(true);
con.setUseCaches(false);
con.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
OutputStreamWriter osw = new OutputStreamWriter(con.getOutputStream(), "UTF-8");
osw.write(sb.toString());
osw.flush();
osw.close();
} catch (Exception e) {
e.printStackTrace();
} finally {
if (con != null) {
con.disconnect();
}
}

// 读取返回内容
StringBuffer buffer = new StringBuffer();
try {
//一定要有返回值，否则无法把请求发送给server端。
BufferedReader br = new BufferedReader(new InputStreamReader(con.getInputStream(), "UTF-8"));
String temp;
while ((temp = br.readLine()) != null) {
buffer.append(temp);
buffer.append("\n");
}
} catch (Exception e) {
e.printStackTrace();
}

return buffer.toString();
}

}

 备注：一定要获取返回值，否则请求无法到达。
readLine()为阻塞方法，会等待服务器的响应，否则会一直等待
con.setDoOutput(true); 这个表示是要发送请求到URL地址，没有这句话server是不会响应的。

参数的传递方式类似于在URL后面添加"?key=value&key1=value1"这种方式
 
 
测试类

@Test
public void test3() {
Map parames = new HashMap<String, String>();
parames.put("param1", "param1_value");
parames.put("param2", "param2_value");
parames.put("param3", "param3_value");
// 如果地址栏中有aaa这个参数，则默认选择地址栏的，如果没有则选择添加的参数
parames.put("aaa", "aaa_value");
HttpUtil.http("http://localhost:8080/a/Abc?aaa=dddd", parames);
}