Http通信概述
Http通信主要有两种方式POST方式和GET方式。前者通过Http消息实体发送数据给服务器,安全性高,数据传输大小没有限制,后者通过URL的查询字符串传递给服务器参数,以明文显示在浏览器地址栏,保密性差,最多传输2048个字符。但是GET请求并不是一无是处——GET请求大多用于查询(读取资源),效率高。POST请求用于注册、登录等安全性较高且向数据库中写入数据的操作。
除了POST和GET,http通信还有其他方式!请参见http请求的方法
编码前的准备
在进行编码之前,我们先创建一个Servlet,该Servlet接收客户端的参数(name和age),并响应客户端。
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@WebServlet (urlPatterns={ "/demo.do" }) public class DemoServlet extends HttpServlet { private static final long serialVersionUID = 1L; public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { request.setCharacterEncoding( "utf-8" ); response.setContentType( "text/html;charset=utf-8" ); String name = request.getParameter( "name" ); String age = request.getParameter( "age" ); PrintWriter pw = response.getWriter(); pw.print( "您使用GET方式请求该Servlet。<br />" + "name = " + name + ",age = " + age); pw.flush(); pw.close(); } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { request.setCharacterEncoding( "utf-8" ); response.setContentType( "text/html;charset=utf-8" ); String name = request.getParameter( "name" ); String age = request.getParameter( "age" ); PrintWriter pw = response.getWriter(); pw.print( "您使用POST方式请求该Servlet。<br />" + "name = " + name + ",age = " + age); pw.flush(); pw.close(); } } |
使用JDK实现http通信
使用URLConnection实现GET请求
实例化一个java.net.URL对象;
通过URL对象的openConnection()方法得到一个java.net.URLConnection;
通过URLConnection对象的getInputStream()方法获得输入流;
读取输入流;
关闭资源。
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public void get() throws Exception{ URL url = new URL( "http://127.0.0.1/http/demo.do?name=Jack&age=10" ); URLConnection urlConnection = url.openConnection(); // 打开连接 BufferedReader br = new BufferedReader( new InputStreamReader(urlConnection.getInputStream(), "utf-8" )); // 获取输入流 String line = null ; StringBuilder sb = new StringBuilder(); while ((line = br.readLine()) != null ) { sb.append(line + "\n" ); } System.out.println(sb.toString()); } |
使用HttpURLConnection实现POST请求
java.net.HttpURLConnection是java.net.URL的子类,提供了更多的关于http的操作(getXXX 和 setXXX方法)。该类中定义了一系列的HTTP状态码:
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public void post() throws IOException{ URL url = new URL( "http://127.0.0.1/http/demo.do" ); HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection(); httpURLConnection.setDoInput( true ); httpURLConnection.setDoOutput( true ); // 设置该连接是可以输出的 httpURLConnection.setRequestMethod( "POST" ); // 设置请求方式 httpURLConnection.setRequestProperty( "charset" , "utf-8" ); PrintWriter pw = new PrintWriter( new BufferedOutputStream(httpURLConnection.getOutputStream())); pw.write( "name=welcome" ); // 向连接中输出数据(相当于发送数据给服务器) pw.write( "&age=14" ); pw.flush(); pw.close(); BufferedReader br = new BufferedReader( new InputStreamReader(httpURLConnection.getInputStream(), "utf-8" )); String line = null ; StringBuilder sb = new StringBuilder(); while ((line = br.readLine()) != null ) { // 读取数据 sb.append(line + "\n" ); } System.out.println(sb.toString()); } |
使用httpclient进行http通信
httpclient大大简化了JDK中http通信的实现。
maven依赖:
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<dependency> <groupId>org.apache.httpcomponents</groupId> <artifactId>httpclient</artifactId> <version> 4.3 . 6 </version> </dependency> |
GET请求
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public void httpclientGet() throws Exception{ // 创建HttpClient对象 HttpClient client = HttpClients.createDefault(); // 创建GET请求(在构造器中传入URL字符串即可) HttpGet get = new HttpGet( "http://127.0.0.1/http/demo.do?name=admin&age=40" ); // 调用HttpClient对象的execute方法获得响应 HttpResponse response = client.execute(get); // 调用HttpResponse对象的getEntity方法得到响应实体 HttpEntity httpEntity = response.getEntity(); // 使用EntityUtils工具类得到响应的字符串表示 String result = EntityUtils.toString(httpEntity, "utf-8" ); System.out.println(result); } |
POST请求
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public void httpclientPost() throws Exception{ // 创建HttpClient对象 HttpClient client = HttpClients.createDefault(); // 创建POST请求 HttpPost post = new HttpPost( "http://127.0.0.1/http/demo.do" ); // 创建一个List容器,用于存放基本键值对(基本键值对即:参数名-参数值) List<BasicNameValuePair> parameters = new ArrayList<>(); parameters.add( new BasicNameValuePair( "name" , "张三" )); parameters.add( new BasicNameValuePair( "age" , "25" )); // 向POST请求中添加消息实体 post.setEntity( new UrlEncodedFormEntity(parameters, "utf-8" )); // 得到响应并转化成字符串 HttpResponse response = client.execute(post); HttpEntity httpEntity = response.getEntity(); String result = EntityUtils.toString(httpEntity, "utf-8" ); System.out.println(result); } |
HttpClient是Apache Jakarta Common下的子项目,用来提供高效的、最新的、功能丰富的支持HTTP协议的客户端编程工具包,并且它支持HTTP协议最新的版本和建议。HttpClient已经应用在很多的项目中,比如Apache Jakarta上很著名的另外两个开源项目Cactus和HTMLUnit都使用了HttpClient。