URLConnection发送HTTP请求的方法_动力节点Java学院整理

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。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.bjpowernode.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.bjpowernode.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，

1. 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）
2. 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.bjpowernode.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.bjpowernode.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>