杨校老师课堂之Servlet的重构为BaseServlet的步骤【内含视频讲解】

杨校

发布于 2022-05-07 15:01:56

1830

发布于 2022-05-07 15:01:56

创建Servlet、命名为BaseServlet继承HttpServlet，只需要覆写一个方法，即service方法
写你需要用到的Servlet，比方：UserServlet | DepartmentServlet | EmployeeServlet等但是他们不用再去继承HttpServlet，而是要去继承BaseServlet

以下BaseServlet，没有采用注解。依旧是使用web.xml作为配置

package cn.javabs.commons;

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.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

//@WebServlet(name = "BaseServlet"，urlPatterns = {"/baseServlet"})
public class BaseServlet extends HttpServlet {

    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        String uri = req.getRequestURI();

        System.out.println("uri:" + uri);//uri:     /userServlet/addUser


        int position = uri.lastIndexOf('/');
        System.out.println("position:" + position); //  position:     12

        String methodName = uri.substring(position+1);//position+1: 最后一个斜线后的字母，也就是我们想要单词的首字母
        System.out.println("methodName:" +  methodName);// methodName:     /addUser

//        ----
        System.out.println("this代表的是："+this);//this代表的是：cn.javabs.commons.UserServlet@49220d

        try {
            // 不会忽略访问权限修饰符  只识别public修饰的方法
//            method    = this.getClass().getMethod(methodName, HttpServletRequest.class, HttpServletResponse.class);
            // 会忽略访问权限修饰符
            Method   method    = this.getClass().getDeclaredMethod(methodName, HttpServletRequest.class, HttpServletResponse.class);
            System.out.println("method:"+ method);

            String pageName  = (String) method.invoke(this,req,resp);
            System.out.println("pageName:" + pageName);

            if (pageName==null || pageName.equals("")){
                resp.sendRedirect(req.getContextPath()+"/404.jsp");
            }else{
                // 判断 返回得字符串中是否又冒号存在！
                if (pageName.contains(":")){

                    // 以冒号分割 pageName
                    String[] datas = pageName.split(":");
                    System.out.println("数组的长度："+datas.length);
                    System.out.println("冒号左边的数据："+datas[0]);
                    System.out.println("冒号右边的数据："+datas[1]);

                    // 进行判断  固定的字符串"forward" 与 我们得到的左侧数据  进行判断是否相同(忽略大小写)
                    if("forward".equalsIgnoreCase(datas[0])){
                        req.getRequestDispatcher("/"+datas[1]+".jsp").forward(req,resp);
                    }
                    // 进行判断  固定的字符串"redirect" 与 我们得到的左侧数据  进行判断是否相同(忽略大小写)
                    else if("redirect".equalsIgnoreCase(datas[0])){
                        resp.sendRedirect(req.getContextPath()+"/"+datas[1]+".jsp");
                    }
                }else{// 没有冒号，即代表没有指定是转发或者重定向、一律按照转发处理！
                    req.getRequestDispatcher("/"+pageName+".jsp").forward(req,resp);
                }
            }
        } catch (NoSuchMethodException e) {
           throw  new RuntimeException("BaseServlet出现了NoSuchMethodException异常" + e);
        } catch (IllegalAccessException e) {
            throw  new RuntimeException("BaseServlet出现了IllegalAccessException异常" + e);
        } catch (InvocationTargetException e) {
            throw  new RuntimeException("BaseServlet出现了InvocationTargetException异常" + e);
        }
    }
}

以下Servlet，全部是继承的BaseServlet，也可以理解为是测试使用的Servlet

页面

<%--
  Created by IntelliJ IDEA.
  User: Mryang
  Date: 2019/4/26
  Time: 14:01
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
  <head>
    <title>$Title$</title>
  </head>
  <body>
  <a href="${pageContext.request.contextPath}/userServlet/addUser">添加用户</a>
  <a href="${pageContext.request.contextPath}/userServlet/editUser">编辑用户</a>
  <a href="${pageContext.request.contextPath}/userServlet/delUser">删除用户</a>
  <a href="${pageContext.request.contextPath}/userServlet/findUser">查询用户</a>
  <hr/>
  <a href="${pageContext.request.contextPath}/userServlet/xxx">没有对应的方法</a>
  <hr/>
  <a href="${pageContext.request.contextPath}/departmentServlet/addDept">添加部门注解</a>
  <a href="${pageContext.request.contextPath}/bookServlet/addBook">添加图书配置文件</a>
  <hr/>
  </body>
</html>

以下是测试的Servlet（有配置文件的，也有注解方式的）

第一个UserServlet

package cn.javabs.web.servlet;

import cn.javabs.commons.BaseServlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class UserServlet extends BaseServlet {
    /**
     * 添加用户
     * @param request
     * @param response
     * @throws ServletException
     * @throws IOException
     */
    public String addUser(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("添加用户方法被index.jsp调用执行了");

        // request.getRequestDispatcher("/main.jsp").forward(request,response);
        // 会将return的内容字符串发送给BaseServlet中得PageName 变量接受接受得
        return "forward:main";
    }

    /**
     * 编辑用户
     * @param request
     * @param response
     * @throws ServletException
     * @throws IOException
     */
    protected String editUser(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("编辑用户方法被index.jsp调用执行了");
        // response.sendRedirect(request.getContextPath()+"/success.jsp");
        // 会将return的内容字符串发送给BaseServlet中得PageName 变量接受接受得
        return  "redirect:success";
    }

    /**
     * 删除用户
     * @param request
     * @param response
     * @throws ServletException
     * @throws IOException
     */
    protected String delUser(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("删除用户方法被index.jsp调用执行了");
        return "right";
    }

    /**
     * 查询用户
     * @param request
     * @param response
     * @throws ServletException
     * @throws IOException
     */
    protected String findUser(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("查询用户方法被index.jsp调用执行了");
        return "";
    }
}

第二个BookServlet

package cn.javabs.web.servlet;

import cn.javabs.commons.BaseServlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class BookServlet extends BaseServlet {
    public String addBook(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("添加图书成功");
      return  "success";
    }

    public String editBook(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        return  "redirect:main";
    }
}

第三个测试Servlet，我们采用注解的方式：

package cn.javabs.web.servlet;

import cn.javabs.commons.BaseServlet;

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(urlPatterns = {"/departmentServlet/*"})
public class DepartmentServlet extends BaseServlet {
    public String addDept(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        System.out.println("添加部门成功");
        return  "success";
    }

    public String editDept(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        return  "redirect:main";
    }
}

配置文件 web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://java.sun.com/xml/ns/javaee"
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
           xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
		  http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
           version="3.0">
   <!--BaseServlet的配置-->
    <servlet>
        <servlet-name>BaseServlet</servlet-name>
        <servlet-class>cn.javabs.commons.BaseServlet</servlet-class>
    </servlet>
   <!--注意:没有使用通配符-->
    <servlet-mapping>
        <servlet-name>BaseServlet</servlet-name>
        <url-pattern>/baseServlet</url-pattern>
    </servlet-mapping>

    <!--UserServlet的配置-->
    <servlet>
        <servlet-name>UserServlet</servlet-name>
        <servlet-class>cn.javabs.web.servlet.UserServlet</servlet-class>
    </servlet>
    <!--注意:url中的属性值后需要有通配符-->
    <servlet-mapping>
        <servlet-name>UserServlet</servlet-name>
        <url-pattern>/userServlet/*</url-pattern>
    </servlet-mapping>

   <!--BookServlet的配置-->
    <servlet>
        <servlet-name>BookServlet</servlet-name>
        <servlet-class>cn.javabs.web.servlet.BookServlet</servlet-class>
    </servlet>
    
    <!--注意:url中的属性值后需要有通配符-->
    <servlet-mapping>
        <servlet-name>BookServlet</servlet-name>
        <url-pattern>/bookServlet/*</url-pattern>
    </servlet-mapping>

</web-app>