Servlet - 技术栈

1、什么是Servlet:Servlet是运行在服务端，用来响应客户端请求的对象，这种对象称之为Servlet。

1.1、创建Servlet

网站目录结构：

第一个Servlet程序

java 复制代码

package servlet;

import java .io.*;
import jakarta.servlet.*;
import jakarta.servlet.http.*;
import jakarta.servlet.annotation.WebServlet;

@WebServlet(name="firstServlet",urlPatterns={"/firstServlet"})
public class FirstServlet extends HttpServlet
{
    private static final long serialVersionUID=1L;
    public void init(ServletConfig config) throws ServletException{
        super.init(config);
    }

    public void service(HttpServletRequest request,HttpServletResponse response) throws IOException{
        response.setContentType("text/html;charset=utf8");
        PrintWriter out =response.getWriter();
        out.print("<html><body>");
        out.print("第一个servlet对象");
        out.print("</html></body>");
    }
}

编译Servlet 命令：javac -encoding utf8 -cp web-inf/lib/servlet-api.jar; -d web-inf/classes servlet/FirstServlet.java

1.2使用web.xml部署servlet

1.3使用注解类WebServlet部署servlet

运行结果：

解决前面Servlet编译器报红问题：

练习：

网站目录结构：

Computer.java

java 复制代码

package servlet;

import java.io.*;
import jakarta.servlet.*;
import jakarta.servlet.http.*;
import jakarta.servlet.annotation.WebServlet;

@WebServlet(urlPatterns = {"/computer"})
public class Computer extends HttpServlet{
    public void init(ServletConfig config) throws ServletException{
        super.init(config);
    }

    public void service(HttpServletRequest request,HttpServletResponse response)throws IOException{
        response.setContentType("text/html;charset=utf8");
        PrintWriter out=response.getWriter();
        out.print("<html><body>");

        String length = request.getParameter("length");
        String width = request.getParameter("width");
        double area = 0;

        try{
            double length1=Double.parseDouble(length);
            double width1=Double.parseDouble(width);
            if(length1>=0&&width1>=0){
                out.print("<br>长是"+length1+"宽是"+width1+"矩形的面积：");
                out.print("<br>"+length1*width1);
            }else{
                out.print("<br>矩形的长和宽不能是负数");
            }

        }catch(NumberFormatException e){
            out.print("<H1>请输入数字字符</H1>");
        }
        out.println("</body></html>");
    }

    
}

编译Servlet 命令：javac -encoding utf8 -cp web-inf/lib/servlet-api.jar; -d web-inf/classes servlet/Computer.java

example5_1.jsp

java 复制代码

<%@page language="java" contentType="text/html;charset=utf8"%>
<html>
    <body>
        <font size="3">
            <form action="computer" method="post">
            <br>请输入矩形的长：
            <input type ="text" name="length"/>
            <br>请输入矩形的宽：
            <input type ="text" name="width"/>
            <br>
            <input type="submit" value="提交"/>
            </form>
        </font>

    </body>
</html>

运行结果：

ShowLetter.java

java 复制代码

package servlet;

import java.io.*;
import jakarta.servlet.*;
import jakarta.servlet.http.*;
import jakarta.servlet.annotation.WebServlet;

@WebServlet(urlPatterns = {"/letter"})
public class ShowLetter extends HttpServlet {
    public void init(ServletConfig config) throws ServletException{
        super.init(config);
    }
    public void service(HttpServletRequest request,HttpServletResponse response)throws IOException{
        response.setContentType("text/html;charset=utf8");
        PrintWriter out=response.getWriter();
        out.print("<html><body>");
        out.print("<br>小写字母：");
        for(char c='a';c<='z';c++){
            out.print(" "+c);
        }

        out.print("<br>大写字母：");
        for(char c='A';c<='Z';c++){
            out.print(" "+c);
        }
        out.println("</body></html>");
    }
    
}

编译Servlet 命令：javac -encoding utf8 -cp web-inf/lib/servlet-api.jar; -d web-inf/classes servlet/ShowLetter.java

example5_2.jsp

java 复制代码

<%@page language="java" contentType="text/html;charset=utf8"%>
<html>
<body>
<font size=3>
单击超链接查看英语字母表：
<br><a href="letter">查看英语字母表</a>
</font>
</body>
</html>

运行结果：