简单的Filter+Servlet+反射，实现Servlet中有多个方法可以执行

  之前用Servlet写项目，方法里面只有两个方法 doGet和doPost 方法，现在运用Filter 和 反射的方法，再也不用担心需要写很多的Servlet了，话不多少，讲解后直接撸代码。

之前的思路

网页跳转到Servlet中，然后Servlet进行跳转（servlet需要在web.xml中配置，若有很多Servlet，则很麻烦），servlet处理后，根据request.sendRedirect()或者request.getRequestDispatcher().forward(request,response)进行跳转，跳转到JSP页面中。

加上Filter+反射后

  这个图好丑，但是可以看懂

话不多说，开始撸代码

只把关键代码写出了，详细代码，大家可以去github上Fork下来

第一步：网页发送请求

<%@ page contentType="text/html;charset=UTF-8" language="java" %>


    


LOOK  

第二步 Filter进行拦截（web.xml中设置Filter对所以的请求进行拦截）

package filter;



import org.apache.commons.lang.StringUtils;

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

/**
 * Created by LENOVO on 2017/9/5.
 */
public class BackServletFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {

    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {

        HttpServletResponse response = (HttpServletResponse)servletResponse;
        HttpServletRequest request = (HttpServletRequest)servletRequest;
       /* 假定你的web application 名称为news,你在浏览器中输入请求路径：
        http://localhost:8080/news/main/list.jsp
        则执行下面向行代码后打印出如下结果：
        1、 System.out.println(request.getContextPath());
        打印结果：/news
        2、System.out.println(request.getServletPath());
        打印结果：/main/list.jsp
        3、 System.out.println(request.getRequestURI());
        打印结果：/news/main/list.jsp
        4、 System.out.println(request.getRealPath("/"));
        打印结果：F:\Tomcat 6.0\webapps\news\test*/

        String contextPath = request.getServletContext().getContextPath();

        String uri = request.getRequestURI();

        uri = StringUtils.remove(uri,contextPath);

        if(uri.startsWith("/admin_")){
            String servletPath = StringUtils.substringBetween(uri,"_","_")+"Servlet";
            String method = StringUtils.substringAfterLast(uri,"_");
            request.setAttribute("method",method);
            request.getRequestDispatcher("/"+servletPath).forward(request,response);
            return ;
        }

        filterChain.doFilter(request,response);

    }

    @Override
    public void destroy() {

    }
}

第三步：跳转到对应的Servlet（只实现了查看的功能）

package servlet;

import po.Category;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.util.List;

/**
 * Created by LENOVO on 2017/9/5.
 */
public class CategoryServlet extends BackServlet{
    @Override
    public String add(HttpServletRequest request, HttpServletResponse response) {
        return null;
    }

    @Override
    public String delete(HttpServletRequest request, HttpServletResponse response) {
        return null;
    }

    @Override
    public String edit(HttpServletRequest request, HttpServletResponse response) {
        return null;
    }

    @Override
    public String update(HttpServletRequest request, HttpServletResponse response) {
        return null;
    }

    @Override
    public String list(HttpServletRequest request, HttpServletResponse response) {
         List list = categoryDao.getAll();


         request.setAttribute("list",list);
         return "/WEB-INF/jsp/list.jsp";
    }
}

第四步：调用继承类的service 方法。（

1. 在servlet中默认情况下，无论你是get还是post 提交过来 都会经过service（）方法来处理，然后转向到doGet 
2. 或是doPost方法，

）

package servlet;

import dao.CategoryDao;

import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.lang.reflect.Method;

/**
 * Created by LENOVO on 2017/9/5.
 */
public abstract  class BackServlet extends HttpServlet{
    public abstract String add(HttpServletRequest request, HttpServletResponse response);

    public abstract String delete(HttpServletRequest request, HttpServletResponse response);

    public abstract String edit(HttpServletRequest request, HttpServletResponse response);

    public abstract String update(HttpServletRequest request, HttpServletResponse response);

    public abstract String list(HttpServletRequest request, HttpServletResponse response  );

    protected CategoryDao categoryDao = new CategoryDao();

    public void service(HttpServletRequest request, HttpServletResponse response) {
        try {


			/*借助反射，调用对应的方法*/
            String method = (String) request.getAttribute("method");
            Method m = this.getClass().getMethod(method, HttpServletRequest.class,
                    HttpServletResponse.class);
            String redirect = m.invoke(this, request, response).toString();

			/*根据方法的返回值，进行相应的客户端跳转，服务端跳转，或者仅仅是输出字符串*/

            if (redirect.startsWith("@"))
                response.sendRedirect(redirect.substring(1));
            else if (redirect.startsWith("%"))
                response.getWriter().print(redirect.substring(1));
            else
                request.getRequestDispatcher(redirect).forward(request, response);

        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
            throw new RuntimeException(e);
        }
    }
}

第五步：页面跳转

<%--
  Created by IntelliJ IDEA.
  User: LENOVO
  Date: 2017/9/1
  Time: 18:34
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>


    





        

    

        
ID
        
Name
        
Age
Password
        
修改
        
删除
    
    

            
${student.id}
            
${student.name}
            
${student.age}
            
${student.password}
            
修改
            
删除
        
    

第七步：其他的工具类 和Dao层

package util;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

/**
 * Created by LENOVO on 2017/9/5.
 */
public class DButil {
    static  String ip = "127.0.0.1";
    static int port = 3306 ;
    static String database = "blog";
    static String encoding = "UTF-8";
    static String loginName = "root" ;
    static String password = "root";

    static {
        try  {
            Class.forName("com.mysql.jdbc.Driver");
        }catch (ClassNotFoundException e){
            e.printStackTrace();
        }
    }

    public static Connection getConnection() throws SQLException{
        String url = String.format("jdbc:mysql://%s:%d/%s?characterEncoding=%s",ip,port,database,encoding);
        return DriverManager.getConnection(url,loginName,password);
    }
}

package dao;

import po.Category;
import util.DButil;


import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;

/**
 * Created by LENOVO on 2017/9/5.
 */
public class CategoryDao {
    public List getAll(){
        String sql = "select * from category ";
        //要把这个定义写到这里，如果写到try，catch中，就成为局部函数，不能当做返回值了
        List categoryList = new ArrayList<>();
        try (Connection connection = DButil.getConnection();
             PreparedStatement preparedStatement = connection.prepareStatement(sql)){
            ResultSet resultSet = preparedStatement.executeQuery();
             while(resultSet.next()){
                 Category category = new Category();
                 category.setId(resultSet.getInt("id"));
                 category.setName(resultSet.getString("name"));
                 category.setAge(resultSet.getInt("age"));
                 category.setPassword(resultSet.getString("password"));
                 categoryList.add(category);
             }
        }catch(SQLException e){
                 e.printStackTrace();
        }
        return categoryList;
    }

}

好了，应该可以运行成功了  ，还有数据库 

我的github地址  https://github.com/boheningmeng/170905_Filter