Servlet的使用
1.Servlet的含义
Servlet 是一种实现动态页面的技术. 是一组 Tomcat 提供给程序猿的 API, 帮助程序猿简单高效的开发一个 web app。
Servlet 就是 Tomcat 这个 HTTP 服务器提供给 Java 的一组 API, 来完成构建动态页面这个任务。
2.Servlet 的生命周期。
生命周期即他每个阶段需要干的事情:
Servlet每个阶段的工作:
1.开始的时候,执行init;
2.每次收到请求,执行service;
3.销毁之前,执行destroy;
一个servlet程序,里面可以包含多个servlet,某个servlet的生死,不影响整个servlet的使用;
3.代码案例
3.1显示 HttpServletRequest 的常用属性
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
@WebServlet("/showRequest")
public class showRequest extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {//搞个StringBuilder,把这些api的结果,统一写回到响应中StringBuilder stringBuilder = new StringBuilder();stringBuilder.append(req.getProtocol());stringBuilder.append(req.getMethod());stringBuilder.append(req.getRequestURI());stringBuilder.append(req.getContextPath());stringBuilder.append(req.getQueryString());resp.getWriter().write(stringBuilder.toString());}
}
3.2 获取GET请求中的query string 的内容
请求形如 /message?aa=10&bb=20
在Servlet 代码中获取到 aa 和 bb 的值, 并显示在页面上
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;@WebServlet("/message")
public class GetString extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {String aa = req.getParameter("aa");String bb = req.getParameter("bb");resp.setContentType("text/html");resp.getWriter().write("aa = "+aa+" bb = "+bb);}
}
3.3获取 POST 请求中 body 的内容
分别实现这两种 body 格式的处理:
- aa=10&bb=20
- { "aa": 10, "bb":20}
把 aa 和 bb 的值获取到, 展示到页面上.
第一种:
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;@WebServlet("/message")
public class GetString extends HttpServlet {@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {String aa = req.getParameter("aa");String bb = req.getParameter("bb");resp.setContentType("text/html");resp.getWriter().write("aa = "+aa+" classId = "+bb);}}
<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta http-equiv="X-UA-Compatible" content="ie=edge"><title>Document</title>
</head>
<body>
<!-- <form action="postParameter" method="post">-->
<!-- <input type="text" name="studentId">-->
<!-- <input type="text" name="classId">-->
<!-- <input type="submit" value="提交">-->
<!-- </form>--><form action="message" method="post"><input type="text" name="aa"><input type="text" name="bb"><input type="submit" value="提交"></form><!-- 使用这个页面来构造ajax请求 --><script src="https://cdn.bootcdn.net/ajax/libs/jquery/3.6.4/jquery.min.js"></script><script>// $.ajax({// type: 'get',// //url: 'method',// //绝对路径// url:'/Hello_Servlet2/method',// success: function(body,status){// console.log(body);// }// });</script>
</body>
</html>
<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta http-equiv="X-UA-Compatible" content="ie=edge"><title>Document</title>
</head>
<body>
<!-- <form action="postParameter" method="post">-->
<!-- <input type="text" name="studentId">-->
<!-- <input type="text" name="classId">-->
<!-- <input type="submit" value="提交">-->
<!-- </form>--><form action="message" method="post"><input type="text" name="aa"><input type="text" name="bb"><input type="submit" value="提交"></form><!-- 使用这个页面来构造ajax请求 --><script src="https://cdn.bootcdn.net/ajax/libs/jquery/3.6.4/jquery.min.js"></script><script>// $.ajax({// type: 'get',// //url: 'method',// //绝对路径// url:'/Hello_Servlet2/method',// success: function(body,status){// console.log(body);// }// });</script>
</body>
</html>
第二种:
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.InputStream;
@WebServlet("/message2")
public class PostJson extends HttpServlet {@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {//super.doPost(req, resp);//通过这个方法来处理body为json格式的数据//直接吧req对象里 body 完整的读取出来//getInputStream//在流对象中读多少个字节,取决于Content-lengthint length = req.getContentLength();byte[] buffer = new byte[length];InputStream inputStream = req.getInputStream();inputStream.read(buffer);//把这个字节数组构造成String,打印出来String body = new String(buffer,0,length,"utf8");System.out.println("body = "+body);//设置返回值的格式类型htmlresp.setContentType("text/html");resp.getWriter().write(body);}
}
使用postman构造post模拟请求: