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。
java
@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。
java
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:
java
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:
xml
<dependency> <groupId>org.apache.httpcomponents</groupId> <artifactId>httpclient</artifactId> <version>4.3.6</version> </dependency>
GET请求
java
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
java
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); }
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