通过java.net.URLConnection发送HTTP请求的方法

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。

运用原生Java Api发送简单的Get请求、Post请求

HTTP请求粗分为两种，一种是GET请求，一种是POST请求。（详细的请见：Hypertext Transfer Protocol -- HTTP/1.1 - Method Definitions）

使用Java发送这两种请求的代码大同小异，只是一些参数设置的不同。步骤如下：

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

简单的Get请求示例如下：

package com.nicchagil.httprequestdemo;

import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLConnection;

public class HttpGetRequest {

    /**
     * Main
     * @param args
     * @throws Exception 
     */
    public static void main(String[] args) throws Exception {
        System.out.println(doGet());
    }
    
    /**
     * Get Request
     * @return
     * @throws Exception
     */
    public static String doGet() throws Exception {
        URL localURL = new URL("http://localhost:8080/OneHttpServer/");
        URLConnection connection = localURL.openConnection();
        HttpURLConnection httpURLConnection = (HttpURLConnection)connection;
        
        httpURLConnection.setRequestProperty("Accept-Charset", "utf-8");
        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;
        
        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();
    }
    
}

简单的Post请求示例如下：

package com.nicchagil.httprequestdemo;

import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLConnection;

public class HttpPostRequest {

    /**
     * Main
     * @param args
     * @throws Exception 
     */
    public static void main(String[] args) throws Exception {
        System.out.println(doPost());
    }
    
    /**
     * Post Request
     * @return
     * @throws Exception
     */
    public static String doPost() throws Exception {
        String parameterData = "username=nickhuang&blog=http://www.cnblogs.com/nick-huang/";
        
        URL localURL = new URL("http://localhost:8080/OneHttpServer/");
        URLConnection connection = localURL.openConnection();
        HttpURLConnection httpURLConnection = (HttpURLConnection)connection;
        
        httpURLConnection.setDoOutput(true);
        httpURLConnection.setRequestMethod("POST");
        httpURLConnection.setRequestProperty("Accept-Charset", "utf-8");
        httpURLConnection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
        httpURLConnection.setRequestProperty("Content-Length", String.valueOf(parameterData.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(parameterData.toString());
            outputStreamWriter.flush();
            
            if (httpURLConnection.getResponseCode() >= 300) {
                throw new Exception("HTTP Request is not success, Response code is " + httpURLConnection.getResponseCode());
            }
            
            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();
    }

}

简单封装

如果项目中有多处地方使用HTTP请求，我们适当对其进行封装，

• 可以大大减少代码量（不需每次都写一大段原生的请求Source code）
• 也可以使配置更灵活、方便（全局设置一些项目特有的配置，比如已商榷的time out时间、已确定的Proxy Server，避免以后改动繁琐）

以下简单封装成HttpRequestor，以便使用：

package com.nicchagil.util.httprequestor;

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 = 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;
        
        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 = 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();
            
            if (httpURLConnection.getResponseCode() >= 300) {
                throw new Exception("HTTP Request is not success, Response code is " + httpURLConnection.getResponseCode());
            }
            
            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;
    }
    
}

   

写一个调用的测试类：

package com.nicchagil.util.httprequestor;

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

public class Call {

    public static void main(String[] args) throws Exception {
        
        /* Post Request */
        Map dataMap = new HashMap();
        dataMap.put("username", "Nick Huang");
        dataMap.put("blog", "IT");
        System.out.println(new HttpRequestor().doPost("http://localhost:8080/OneHttpServer/", dataMap));
        
        /* Get Request */
        System.out.println(new HttpRequestor().doGet("http://localhost:8080/OneHttpServer/"));
    }

}

OK，完成！！

简单测试

以上的请求地址都是http://localhost:8080/OneHttpServer/

这是自己的一个用于测试的Web Application，就一个简单的Servlet和web.xml。毕竟需要测试请求参数是否能正常接收，处理超时的情况。

LoginServlet

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 LoginServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
       
    public LoginServlet() {
        super();
    }

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

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        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");
        response.getWriter().write("It is ok!");
    }

}

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">
  <display-name>OneHttpServer</display-name>
  <welcome-file-list>
    <welcome-file>LoginServlet</welcome-file>
  </welcome-file-list>
  
  <servlet>
    <description></description>
    <display-name>LoginServlet</display-name>
    <servlet-name>LoginServlet</servlet-name>
    <servlet-class>LoginServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>LoginServlet</servlet-name>
    <url-pattern>/LoginServlet</url-pattern>
  </servlet-mapping>
  
</web-app>