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);    }}

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;    }}

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);    }}