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。

Kick start

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Source Code大同小异，只是一些参数设置的不同。步骤如下：

通过统一资源定位器（java.net.URL）获取连接器（java.net.URLConnection）
设置请求的参数
发送请求
以输入流的形式获取返回内容
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();
}

}

HttpGetRequest

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();
}

}

HttpPostRequest

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;
}

}

HttpRequestor

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/"));
}

}

Call

OK，完成！！

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!");
}

}

LoginServlet

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>

web.xml

感觉自己萌萌哒!~~