一、前言

如何通过Java发送HTTP请求，通俗点讲，如何通过Java（模拟浏览器）发送HTTP请求。

Java有原生的API可用于发送HTTP请求，即java.net.URL、java.net.URLConnection，这些API很好用、很常用，但不够简便；

所以，也流行有许多Java HTTP请求的framework，如，Apache的HttpClient。

目前项目主要用到Java原生的方式，所以，这里主要介绍此方式。

二、运用原生Java Api发送简单的Get请求、Post请求步骤

       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

三、发送请求与接收响应流类 HttpRequestor

package me.http;

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.InetSocketAddress;
import java.net.Proxy;
import java.net.URL;
import java.net.URLConnection;
import java.util.Iterator;
import java.util.Map;

public class HttpRequestor {
 
 private String charset = "utf-8";
 private Integer connectTimeout = null;
 private Integer socketTimeout = null;
 private String proxyHost = null;
 private Integer proxyPort = null;
 
 /**
  * Do GET request
  * @param url
  * @return
  * @throws Exception
  * @throws IOException
  */
 public String doGet(String url) throws Exception {
  
  URL localURL = new URL(url);
  
  URLConnection connection = this.openConnection(localURL);
  HttpURLConnection httpURLConnection = (HttpURLConnection)connection;
  
  httpURLConnection.setRequestProperty("Accept-Charset", charset);
  httpURLConnection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
  
  InputStream inputStream = null;
  InputStreamReader inputStreamReader = null;
  BufferedReader reader = null;
  StringBuffer resultBuffer = new StringBuffer();
  String tempLine = null;
  //响应失败
  if (httpURLConnection.getResponseCode() >= 300) {
   throw new Exception("HTTP Request is not success, Response code is " + httpURLConnection.getResponseCode());
  }
  
  try {
   inputStream = httpURLConnection.getInputStream();
   inputStreamReader = new InputStreamReader(inputStream);
   reader = new BufferedReader(inputStreamReader);
   
   while ((tempLine = reader.readLine()) != null) {
    resultBuffer.append(tempLine);
   }
   
  } finally {
   
   if (reader != null) {
    reader.close();
   }
   
   if (inputStreamReader != null) {
    inputStreamReader.close();
   }
   
   if (inputStream != null) {
    inputStream.close();
   }
   
  }

  return resultBuffer.toString();
 }
 
 /**
  * Do POST request
  * @param url
  * @param parameterMap
  * @return
  * @throws Exception 
  */
 public String doPost(String url, Map parameterMap) throws Exception {
  
  /* Translate parameter map to parameter date string */
  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("&");
    }
   }
  }
  
  System.out.println("POST parameter : " + parameterBuffer.toString());
  
  URL localURL = new URL(url);
  
  URLConnection connection = this.openConnection(localURL);
  HttpURLConnection httpURLConnection = (HttpURLConnection)connection;
  
  httpURLConnection.setDoOutput(true);
  httpURLConnection.setRequestMethod("POST");
  httpURLConnection.setRequestProperty("Accept-Charset", charset);
  httpURLConnection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
  httpURLConnection.setRequestProperty("Content-Length", String.valueOf(parameterBuffer.length()));
  
  OutputStream outputStream = null;
  OutputStreamWriter outputStreamWriter = null;
  InputStream inputStream = null;
  InputStreamReader inputStreamReader = null;
  BufferedReader reader = null;
  StringBuffer resultBuffer = new StringBuffer();
  String tempLine = null;
  
  try {
   outputStream = httpURLConnection.getOutputStream();
   outputStreamWriter = new OutputStreamWriter(outputStream);
   
   outputStreamWriter.write(parameterBuffer.toString());
   outputStreamWriter.flush();
   //响应失败
   if (httpURLConnection.getResponseCode() >= 300) {
    throw new Exception("HTTP Request is not success, Response code is " + httpURLConnection.getResponseCode());
   }
   //接收响应流
   inputStream = httpURLConnection.getInputStream();
   inputStreamReader = new InputStreamReader(inputStream);
   reader = new BufferedReader(inputStreamReader);
   
   while ((tempLine = reader.readLine()) != null) {
    resultBuffer.append(tempLine);
   }
   
  } finally {
   
   if (outputStreamWriter != null) {
    outputStreamWriter.close();
   }
   
   if (outputStream != null) {
    outputStream.close();
   }
   
   if (reader != null) {
    reader.close();
   }
   
   if (inputStreamReader != null) {
    inputStreamReader.close();
   }
   
   if (inputStream != null) {
    inputStream.close();
   }
   
  }

  return resultBuffer.toString();
 }

 private URLConnection openConnection(URL localURL) throws IOException {
  URLConnection connection;
  if (proxyHost != null && proxyPort != null) {
   Proxy proxy = new Proxy(Proxy.Type.HTTP, new InetSocketAddress(proxyHost, proxyPort));
   connection = localURL.openConnection(proxy);
  } else {
   connection = localURL.openConnection();
  }
  return connection;
 }
 
 /**
  * Render request according setting
  * @param request
  */
 private void renderRequest(URLConnection connection) {
  
  if (connectTimeout != null) {
   connection.setConnectTimeout(connectTimeout);
  }
  
  if (socketTimeout != null) {
   connection.setReadTimeout(socketTimeout);
  }
  
 }

 /*
  * Getter & Setter
  */
 public Integer getConnectTimeout() {
  return connectTimeout;
 }

 public void setConnectTimeout(Integer connectTimeout) {
  this.connectTimeout = connectTimeout;
 }

 public Integer getSocketTimeout() {
  return socketTimeout;
 }

 public void setSocketTimeout(Integer socketTimeout) {
  this.socketTimeout = socketTimeout;
 }

 public String getProxyHost() {
  return proxyHost;
 }

 public void setProxyHost(String proxyHost) {
  this.proxyHost = proxyHost;
 }

 public Integer getProxyPort() {
  return proxyPort;
 }

 public void setProxyPort(Integer proxyPort) {
  this.proxyPort = proxyPort;
 }

 public String getCharset() {
  return charset;
 }

 public void setCharset(String charset) {
  this.charset = charset;
 }
 
}

四、为测试方便,新建一个项目,并新建一个Servlet,接收post请求并对HttpRequestor请求响应,发出响应流

LoginServlet.java代码:此处使用了

注解: @WebServlet("/LoginServlet") ,也可以在web.xml配置Servlet

package me.loginServlet;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class LoginServlet
 */
@WebServlet("/LoginServlet")
public class LoginServlet extends HttpServlet {
 private static final long serialVersionUID = 1L;
  
 /**
  * @see HttpServlet#HttpServlet()
  */
 public LoginServlet() {
  super();
  // TODO Auto-generated constructor stub
 }

 /**
  * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
  */
 protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  // TODO Auto-generated method stub
  System.out.println("111");
 }

 /**
  * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
  */
 protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  // TODO Auto-generated method stub
   String username = request.getParameter("username");
   String blog = request.getParameter("blog");
   
   System.out.println(username);
   System.out.println(blog);
   
   response.setContentType("text/plain; charset=UTF-8");
   response.setCharacterEncoding("UTF-8");
//响应流
   response.getWriter().write("It is ok!");
  
 }

}

五.测试类Test.java

package me.http;

import java.util.HashMap;
import java.util.Map;

public class Test {
public static void main(String[] args) {
  /* Post Request */
 Map dataMap = new HashMap();
 dataMap.put("username", "Nick Huang");
 dataMap.put("blog", "IT");
 try {
  System.out.println(new HttpRequestor().doPost("http://localhost:8081/TestProgect2/LoginServlet", dataMap));
  //System.out.println(new HttpRequestor().doGet("http://localhost:8081/TestProgect2/LoginServlet"));
 } catch (Exception e) {
  // TODO Auto-generated catch block
  e.printStackTrace();
 }
 
 /* Get Request */
 
}
}

1.接收post请求类LoginServlet,控制台测试结果

2.HttpRequestor接收LoginServlet返回的流

OK,完成

六.对于接收TestProgect2项目中LoginServlet.java类返回的流,在真实环境中可能是异步接收返回的流的,当一台机器A向另外一台机器B发送请求,B接收到A的信息,将信息处理后,需要将处理结果返回即响应返回给A,A会接收到B返回的信息

可以另外建一个Servlet类HttpListenerServlet.java来专门异步接收返回的信息

package me.http;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;

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

/**
 * Servlet implementation class HttpListenerServlet
 */
@WebServlet("/HttpListenerServlet")
public class HttpListenerServlet extends HttpServlet {
 private static final long serialVersionUID = 1L;
  
 /**
  * @see HttpServlet#HttpServlet()
  */
 public HttpListenerServlet() {
  super();
  // TODO Auto-generated constructor stub
 }

 /**
  * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
  */
 protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  // TODO Auto-generated method stub
 }

 /**
  * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
  */
 protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  // TODO Auto-generated method stub
   InputStream inputStream = null;
   inputStream = request.getInputStream();
   InputStreamReader inputStreamReader = new InputStreamReader(inputStream);
   BufferedReader reader = new BufferedReader(inputStreamReader);
   String tempLine = null;
   StringBuffer resultBuffer=new StringBuffer();
   while ((tempLine = reader.readLine()) != null) {
    resultBuffer.append(tempLine);
   }
   
   System.out.println(resultBuffer.toString());
 }

}