通过自动回复机器人学Mybatis：代码重构（分层）

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);
}
}