通过java.net.URLConnection发送HTTP请求的方法

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());
    }

}

最后感谢这位博主的博文:http://www.cnblogs.com/nick-huang/p/3859353.html