MVC设计模式 - 技术栈

分层架构模式

随着软件工程的规模越来越大，复杂度越来越高，工程中的组件也越来越多。而组件与组件之间的关联过于紧密，导致整个工程变得异常复杂，进而导致开发人员越来越难以掌控整个工程，造成工程开发失败。这就是组件之间的 "紧耦合" 问题。为了解决这个问题，提出了 "高内聚低耦合" 的思想。也就是 "解耦"

高内聚：每个模块尽可能独立完成自己的功能，不依赖于模块外部的代码。
低耦合：模块与模块之间使用接口尽量降低耦合度。

model1两层架构

model2三层架构

MVC设计模式

Javaweb中的mvc

在前后端分离架构中的MVC

使用过滤器解决跨域和字符集问题

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package com.neusoft.emp.filter;
import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
@WebFilter("/*")
public class SetCharFilter implements Filter{
    @Override 
    public void init(FilterConfig filterConfig) throws ServletException { } 
    @Override 
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, 
                     FilterChain filterChain) throws IOException, ServletException { 
        servletRequest.setCharacterEncoding("utf-8");
        servletResponse.setContentType("text/html;charset=utf-8");
        servletResponse.setCharacterEncoding("utf-8");
        filterChain.doFilter(servletRequest, servletResponse); 
    } 
    @Override 
    public void destroy() { }
}

package filter;
import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
@WebFilter("/*")
public class CorsFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {}
    @Override
    public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain)
            throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest)req;
        HttpServletResponse response = (HttpServletResponse)resp;
        //设置允许跨域
        response.setHeader("Access-Control-Allow-Origin", request.getHeader("Origin"));
        //设置开启Cookie
        response.setHeader("Access-Control-Allow-Credentials", "true"); 
        chain.doFilter(req, resp);    
    }
    @Override
    public void destroy() {}
}

po代码

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package com.neusoft.emp.po;
public class Emp {
    private Integer empno;
    private String ename;
    private String job;
    private Integer mgr;
    private String hiredate;
    private Double sal;
    private Double comm;
    private Integer deptno;
    //get/set方法...
}

dto代码

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package com.neusoft.emp.dto;
import java.util.List;
public class PageDto {
    private int totalRow;        //总行数
    private int totalPageNum;    //总页数
    private int preNum;          //上一页
    private int nextNum;         //下一页
    private int pageNum;         //当前页
    private int maxPageNum;      //每页显示最大行数
    private int beginNum;        //开始记录数
    private List list;               //查询返回数据
    //get/set方法...
}

dao代码

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package com.neusoft.emp.dao;
import java.util.List;
import com.neusoft.emp.po.Emp;
public interface EmpDao {
    public int getEmpCount();
    public List<Emp> listEmp(int beginNum,int maxPageNum);
}

package com.neusoft.emp.dao.impl;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;
import com.neusoft.emp.dao.EmpDao;
import com.neusoft.emp.po.Emp;
import com.neusoft.emp.util.DBUtil;
public class EmpDaoImpl implements EmpDao{
    private Connection con = null;
    private PreparedStatement pst = null;
    private ResultSet rs = null;
    @Override
    public int getEmpCount() {
        int count = 0;
        String sql = "select count(*) from emp";
        try {
            con = DBUtil.getConnection();
            pst = con.prepareStatement(sql);
            rs = pst.executeQuery();
            if(rs.next()) {
                count = rs.getInt(1);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            DBUtil.close(rs, pst, con);
        }
        return count;
    }
    @Override
    public List<Emp> listEmp(int beginNum,int maxPageNum) {
        List<Emp> list = new ArrayList();
        String sql = "select * from emp order by empno desc limit ?,?";
        try {
            con = DBUtil.getConnection();
            pst = con.prepareStatement(sql);
            pst.setInt(1, beginNum);
            pst.setInt(2, maxPageNum);
            rs = pst.executeQuery();
            while(rs.next()) {
                Emp e = new Emp();
                e.setEmpno(rs.getInt("empno"));
                e.setEname(rs.getString("ename"));
                e.setJob(rs.getString("job"));
                e.setMgr(rs.getInt("mgr"));
                e.setHiredate(rs.getString("hiredate"));
                e.setSal(rs.getDouble("sal"));
                e.setComm(rs.getDouble("comm"));
                e.setDeptno(rs.getInt("deptno"));
                list.add(e);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            DBUtil.close(rs, pst, con);
        }
        return list;
    }
}

Service代码

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package com.neusoft.emp.service;
import com.neusoft.emp.dto.PageDto;
public interface EmpService {
    public PageDto listEmp(int pageNum,int maxPageNum);
}

package com.neusoft.emp.service.impl;
import java.util.List;
import com.neusoft.emp.dao.EmpDao;
import com.neusoft.emp.dao.impl.EmpDaoImpl;
import com.neusoft.emp.dto.PageDto;
import com.neusoft.emp.po.Emp;
import com.neusoft.emp.service.EmpService;
public class EmpServiceImpl implements EmpService{
    @Override
    public PageDto listEmp(int pageNum,int maxPageNum) {
        int totalRow = 0;          //初始化总行数
        int totalPageNum = 0;      //初始化总页数
        int preNum = 0;            //初始化上一页
        int nextNum = 0;           //初始化下一页
        int beginNum = 0;          //初始化开始记录数
        //创建DAO
        EmpDao dao = new EmpDaoImpl();
        //创建返回值
        PageDto pageDto = new PageDto();
        //获取总行数
        totalRow = dao.getEmpCount();
        //如果查询行数为0，那么直接结束。
        if(totalRow == 0) {
            return pageDto;
        }
        //计算总页数
        //totalPageNum = totalRow/maxPageNum+1;
        if(totalRow%maxPageNum==0) {
            totalPageNum = totalRow/maxPageNum;
        }else {
            totalPageNum = totalRow/maxPageNum+1;
        }
        //当前页数验证
        if(pageNum<=0){
            pageNum = 1;
        }
        if(pageNum>totalPageNum){
            pageNum = totalPageNum;
        }
        //设置上一页和下一页
        preNum = pageNum;
        nextNum = pageNum;
        if(pageNum > 1) {
            preNum--;
        }
        if(pageNum < totalPageNum) {
            nextNum++;
        }
        //计算开始查询记录数
        beginNum = (pageNum - 1) * maxPageNum;
        //开始查询业务数据
        List<Emp> list = dao.listEmp(beginNum, maxPageNum);
        //封装返回数据
        pageDto.setTotalRow(totalRow);
        pageDto.setTotalPageNum(totalPageNum);
        pageDto.setPreNum(preNum);
        pageDto.setNextNum(nextNum);
        pageDto.setPageNum(pageNum);
        pageDto.setMaxPageNum(maxPageNum);
        pageDto.setBeginNum(beginNum);
        pageDto.setList(list);
        return pageDto;
    }
}

controller代码

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package com.neusoft.emp.servlet;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.List;
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 com.fasterxml.jackson.databind.ObjectMapper;
import com.neusoft.emp.dto.PageDto;
import com.neusoft.emp.po.Emp;
import com.neusoft.emp.service.EmpService;
import com.neusoft.emp.service.impl.EmpServiceImpl;
@WebServlet("/listEmp")
public class ListEmpServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) 
                         throws ServletException, IOException {
        Integer pageNum = Integer.valueOf(request.getParameter("pageNum"));
        Integer maxPageNum = Integer.valueOf(request.getParameter("maxPageNum"));
        EmpService service = new EmpServiceImpl();
        PageDto pageDto = service.listEmp(pageNum, maxPageNum);
        PrintWriter out = response.getWriter();
        ObjectMapper om = new ObjectMapper();
        out.print(om.writeValueAsString(pageDto));  
        out.close();
    }
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) 
                            throws ServletException, IOException {
        doGet(request, response);
    }
}