1 package com.imooc.dao;
 2
 3 import java.sql.Connection;
 4 import java.sql.DriverManager;
 5 import java.sql.PreparedStatement;
 6 import java.sql.ResultSet;
 7 import java.sql.SQLException;
 8 import java.util.ArrayList;
 9 import java.util.List;
10
11 import com.imooc.bean.Message;
12
13 /**
14  * 处理与数据库相关的查询操作
15  *
16  */
17 public class MessageDao {
18     public List<Message> queryMessageList(String command,String description){
19         List<Message> messageList = new ArrayList<Message>();
20         try {
21             Class.forName("com.mysql.jdbc.Driver");
22             Connection conn = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/micro_message", "root", "admin");
23             // StringBuilder速度快适合单线程，StringBuffer适合多线程操作大量数据，String每次都是生成新对象，需要垃圾回收。
24             StringBuilder sb = new StringBuilder("select ID,COMMAND,DESCRIPTION,CONTENT from message where 1=1 ");
25             // String sql = "select ID,COMMAND,DESCRIPTION,CONTENT from message";
26             List<String> paramList = new ArrayList<String>();
27             if(null != command && !"".equals(command)){
28                 sb.append(" and COMMAND=?");
29                 paramList.add(command);
30             }
31             if(null != description && !"".equals(description)){
32                 // MySQL中用%表示任意字符，用空格用于连接
33                 sb.append(" and DESCRIPTION like '%' ? '%'");
34                 paramList.add(description);
35             }
36             PreparedStatement pstmt = conn.prepareStatement(sb.toString());
37             for(int i=0;i<paramList.size();i++){
38                 // 给PreparedStatement中预执行SQL语句追加值
39                 pstmt.setString(i+1, paramList.get(i));
40             }
41             ResultSet rs = pstmt.executeQuery();
42             while(rs.next()){
43                 Message message = new Message();
44                 messageList.add(message);// 这里messageList是个容器，只是对message的引用，所以可以提前放入容器中
45                 message.setId(rs.getString("ID"));
46                 message.setCommand(rs.getString("COMMAND"));
47                 message.setDescription(rs.getString("DESCRIPTION"));
48                 message.setContent(rs.getString("CONTENT"));
49             }
50     }catch (ClassNotFoundException e) {
51         e.printStackTrace();
52     }catch (SQLException e) {
53         e.printStackTrace();
54     }
55     return messageList;
56   }
57
58 }
59