【JAVA】通过URLConnection/HttpURLConnection发送HTTP请求的方法（一）

Java原生的API可用于发送HTTP请求

即java.net.URL、java.net.URLConnection，JDK自带的类；

1.通过统一资源定位器（java.net.URL）获取连接器（java.net.URLConnection）

2.设置请求的参数

3.发送请求

4.以输入流的形式获取返回内容

5.关闭输入流

• 封装请求类

   package com.util;
  
   import java.io.BufferedReader;
   import java.io.IOException;
   import java.io.InputStream;
   import java.io.InputStreamReader;
   import java.io.OutputStream;
   import java.io.OutputStreamWriter;
   import java.net.HttpURLConnection;
   import java.net.MalformedURLException;
   import java.net.URL;
   import java.net.URLConnection;
   import java.util.Iterator;
   import java.util.Map;
  
   public class HttpConnectionUtil {
  
       // post请求
       public static final String HTTP_POST = "POST";
  
       // get请求
       public static final String HTTP_GET = "GET";
  
       // utf-8字符编码
       public static final String CHARSET_UTF_8 = "utf-8";
  
       // HTTP内容类型。如果未指定ContentType，默认为TEXT/HTML
       public static final String CONTENT_TYPE_TEXT_HTML = "text/xml";
  
       // HTTP内容类型。相当于form表单的形式，提交暑假
       public static final String CONTENT_TYPE_FORM_URL = "application/x-www-form-urlencoded";
  
       // 请求超时时间
       public static final int SEND_REQUEST_TIME_OUT = 50000;
  
       // 将读超时时间
       public static final int READ_TIME_OUT = 50000;
  
       /**
        *
        * @param requestType
        *            请求类型
        * @param urlStr
        *            请求地址
        * @param body
        *            请求发送内容
        * @return 返回内容
        */
       public static String requestMethod(String requestType, String urlStr, String body) {
  
           // 是否有http正文提交
           boolean isDoInput = false;
           if (body != null && body.length() > 0)
               isDoInput = true;
           OutputStream outputStream = null;
           OutputStreamWriter outputStreamWriter = null;
           InputStream inputStream = null;
           InputStreamReader inputStreamReader = null;
           BufferedReader reader = null;
           StringBuffer resultBuffer = new StringBuffer();
           String tempLine = null;
           try {
               // 统一资源
               URL url = new URL(urlStr);
               // 连接类的父类，抽象类
               URLConnection urlConnection = url.openConnection();
               // http的连接类
               HttpURLConnection httpURLConnection = (HttpURLConnection) urlConnection;
  
               // 设置是否向httpUrlConnection输出，因为这个是post请求，参数要放在
               // http正文内，因此需要设为true, 默认情况下是false;
               if (isDoInput) {
                   httpURLConnection.setDoOutput(true);
                   httpURLConnection.setRequestProperty("Content-Length", String.valueOf(body.length()));
               }
               // 设置是否从httpUrlConnection读入，默认情况下是true;
               httpURLConnection.setDoInput(true);
               // 设置一个指定的超时值（以毫秒为单位）
               httpURLConnection.setConnectTimeout(SEND_REQUEST_TIME_OUT);
               // 将读超时设置为指定的超时，以毫秒为单位。
               httpURLConnection.setReadTimeout(READ_TIME_OUT);
               // Post 请求不能使用缓存
               httpURLConnection.setUseCaches(false);
               // 设置字符编码
               httpURLConnection.setRequestProperty("Accept-Charset", CHARSET_UTF_8);
               // 设置内容类型
               httpURLConnection.setRequestProperty("Content-Type", CONTENT_TYPE_FORM_URL);
               // 设定请求的方法，默认是GET
               httpURLConnection.setRequestMethod(requestType);
  
               // 打开到此 URL 引用的资源的通信链接（如果尚未建立这样的连接）。
               // 如果在已打开连接（此时 connected 字段的值为 true）的情况下调用 connect 方法，则忽略该调用。
               httpURLConnection.connect();
  
               if (isDoInput) {
                   outputStream = httpURLConnection.getOutputStream();
                   outputStreamWriter = new OutputStreamWriter(outputStream);
                   outputStreamWriter.write(body);
                   outputStreamWriter.flush();// 刷新
               }
               if (httpURLConnection.getResponseCode() >= 300) {
                   throw new Exception(
                           "HTTP Request is not success, Response code is " + httpURLConnection.getResponseCode());
               }
  
               if (httpURLConnection.getResponseCode() == HttpURLConnection.HTTP_OK) {
                   inputStream = httpURLConnection.getInputStream();
                   inputStreamReader = new InputStreamReader(inputStream);
                   reader = new BufferedReader(inputStreamReader);
  
                   while ((tempLine = reader.readLine()) != null) {
                       resultBuffer.append(tempLine);
                       resultBuffer.append("\n");
                   }
               }
  
           } catch (MalformedURLException e) {
               // TODO Auto-generated catch block
               e.printStackTrace();
           } catch (IOException e) {
               // TODO Auto-generated catch block
               e.printStackTrace();
           } catch (Exception e) {
               // TODO Auto-generated catch block
               e.printStackTrace();
           } finally {// 关闭流
  
               try {
                   if (outputStreamWriter != null) {
                       outputStreamWriter.close();
                   }
               } catch (Exception e) {
                   // TODO Auto-generated catch block
                   e.printStackTrace();
               }
               try {
                   if (outputStream != null) {
                       outputStream.close();
                   }
               } catch (Exception e) {
                   // TODO Auto-generated catch block
                   e.printStackTrace();
               }
               try {
                   if (reader != null) {
                       reader.close();
                   }
               } catch (Exception e) {
                   // TODO Auto-generated catch block
                   e.printStackTrace();
               }
               try {
                   if (inputStreamReader != null) {
                       inputStreamReader.close();
                   }
               } catch (Exception e) {
                   // TODO Auto-generated catch block
                   e.printStackTrace();
               }
               try {
                   if (inputStream != null) {
                       inputStream.close();
                   }
               } catch (Exception e) {
                   // TODO Auto-generated catch block
                   e.printStackTrace();
               }
           }
           return resultBuffer.toString();
       }
  
       /**
        * 将map集合的键值对转化成：key1=value1&key2=value2 的形式
        *
        * @param parameterMap
        *            需要转化的键值对集合
        * @return 字符串
        */
       public static String convertStringParamter(Map parameterMap) {
           StringBuffer parameterBuffer = new StringBuffer();
           if (parameterMap != null) {
               Iterator iterator = parameterMap.keySet().iterator();
               String key = null;
               String value = null;
               while (iterator.hasNext()) {
                   key = (String) iterator.next();
                   if (parameterMap.get(key) != null) {
                       value = (String) parameterMap.get(key);
                   } else {
                       value = "";
                   }
                   parameterBuffer.append(key).append("=").append(value);
                   if (iterator.hasNext()) {
                       parameterBuffer.append("&");
                   }
               }
           }
           return parameterBuffer.toString();
       }
  
       public static void main(String[] args) throws MalformedURLException {
  
           System.out.println(requestMethod(HTTP_GET, "http://127.0.0.1:8080/test/TestHttpRequestServlet",
                   "username=123&password=我是谁"));
  
       }
   }

  HttpConnectionUtil

• 测试Servlet

   package com.servlet;
  
   import java.io.IOException;
  
   import javax.servlet.ServletException;
   import javax.servlet.http.HttpServlet;
   import javax.servlet.http.HttpServletRequest;
   import javax.servlet.http.HttpServletResponse;
  
   public class TestHttpRequestServelt extends HttpServlet {
  
       @Override
       protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  
           System.out.println("this is a TestHttpRequestServlet");
           request.setCharacterEncoding("utf-8");
  
           String username = request.getParameter("username");
           String password = request.getParameter("password");
  
           System.out.println(username);
           System.out.println(password);
  
           response.setContentType("text/plain; charset=UTF-8");
           response.setCharacterEncoding("UTF-8");
           response.getWriter().write("This is ok!");
  
       }
   }

  TestHttpRequestServelt

• web.xml配置

   <?xml version="1.0" encoding="UTF-8"?>
   <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" id="WebApp_ID" version="3.1">
     <display-name>test</display-name>
  
     <servlet>
         <servlet-name>TestHttpRequestServlet</servlet-name>
         <servlet-class>com.servlet.TestHttpRequestServelt</servlet-class>
     </servlet>
  
     <servlet-mapping>
         <servlet-name>TestHttpRequestServlet</servlet-name>
         <url-pattern>/TestHttpRequestServlet</url-pattern>
     </servlet-mapping>
  
     <welcome-file-list>
       <welcome-file>index.html</welcome-file>
       <welcome-file>index.htm</welcome-file>
       <welcome-file>index.jsp</welcome-file>
       <welcome-file>default.html</welcome-file>
       <welcome-file>default.htm</welcome-file>
       <welcome-file>default.jsp</welcome-file>
     </welcome-file-list>
   </web-app>

  web.xml