通过自动回复机器人学Mybatis：代码重构（分层）

imooc视频学习笔记 ----> URL：http://www.imooc.com/learn/154

ListServlet.java

package com.imooc.servlet;

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

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.imooc.service.ListService;

/**
 * 列表页面初始化控制
 */
@SuppressWarnings("serial")
public class ListServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // 设置编码
        req.setCharacterEncoding("UTF-8");
        // 接受页面的值
        String command = req.getParameter("command");
        String description = req.getParameter("description");
        // 向页面传值
        req.setAttribute("command", command);
        req.setAttribute("description", description);
        // 查询消息列表并传给页面
        ListService listService = new ListService();
        req.setAttribute("messageList", listService.queryMessageList(command, description));
        // 页面跳转
        req.getRequestDispatcher("/WEB-INF/jsp/back/list.jsp").forward(req, resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // TODO Auto-generated method stub
        this.doGet(req, resp);
    }
}

MessageDao.java

package com.imooc.dao;

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

import com.imooc.bean.Message;

public class MessageDao {
    // 数据库驱动
    private static final String JDBC_DRIVER = "org.gjt.mm.mysql.Driver";
    // 数据库地址
    private static final String DB_URL = "jdbc:mysql://localhost:3306/miro_message";
    
    // 用户名与密码
    private static final String USER = "root";
    private static final String PASS = "pass";
    
    private static Connection conn = null;

    // 加载数据库驱动
    static {
        try {
            Class.forName(JDBC_DRIVER);
            conn = DriverManager.getConnection(DB_URL, USER, PASS);
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
    
    // 获取消息列表
    public List<Message> queryMessageList(String command, String description) {
        List<Message> messageList = new ArrayList<>();
        
        // SQL拼接
        StringBuilder sqlBuilder = new StringBuilder();
        sqlBuilder.append("select ID, COMMAND, DESCRIPTION, CONTENT from MESSAGE where 1=1");
        
        List<String> paramList = new ArrayList<>();
        // 判断指令是否为空
        if (command != null && !"".equals(command.trim())) {
            sqlBuilder.append(" and COMMAND=?");
            paramList.add(command);
        }
        // 判断描述是否为空
        if (description != null && !"".equals(description.trim())) {
            sqlBuilder.append(" and DESCRIPTION like '%' ? '%'");
            paramList.add(description);
        }
        
        String sql = sqlBuilder.toString();
        
        PreparedStatement prep = null;
        ResultSet result = null;
        try {
            prep = conn.prepareStatement(sql);
            // 设置SQL参数
            for (int i = 0; i != paramList.size(); ++i) {
                prep.setString(i+1, paramList.get(i)); 
            }
            // 执行查找操作
            result = prep.executeQuery();
            while (result.next()) {
                // 把查找结果放进List里
                Message message = new Message();
                messageList.add(message);
                
                message.setId(result.getString("ID"));
                message.setCommand(result.getString("COMMAND"));
                message.setDescription(result.getString("DESCRIPTION"));
                message.setContent(result.getString("CONTENT"));
            }

        } catch (SQLException e) {
            e.printStackTrace();
        }
        
        // 如果出现异常就返回一个空的List
        return messageList;
    }
}

ListService.java

package com.imooc.service;

import java.util.List;

import com.imooc.bean.Message;
import com.imooc.dao.MessageDao;

/**
 * 
 * 列表相关的业务功能
 *
 */
public class ListService {
    /**
     * 获取消息列表
     */
    public List<Message> queryMessageList(String command, String description) {
        MessageDao dao = new MessageDao();
        return dao.queryMessageList(command, description);
    }
}