1 <?xml version="1.0" encoding="UTF-8" ?>
19 <!DOCTYPE configuration
20     PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
21     "http://mybatis.org/dtd/mybatis-3-config.dtd">
22 
23 <configuration>
33   <environments default="development">
34     <environment id="development">
35       <transactionManager type="JDBC">
36         <property name="" value=""/>
37       </transactionManager>
38       <!-- 加载驱动和连接 -->
39       <dataSource type="UNPOOLED">
40         <property name="driver" value="com.mysql.jdbc.Driver"/>
41         <property name="url" value="jdbc:mysql://127.0.0.1:3306/micro_message"/>
42         <property name="username" value="xxx"/>
43         <property name="password" value="xxx"/>
44       </dataSource>
45     </environment>
46   </environments>
54 </configuration>

 1 /**
 2  * 访问数据库类
 3  */
 4 public class DBAccess {
 5     /**
 6      * 
 7      * @return
 8      * @throws IOException 出现异常先往外抛,抛给DAO层去处理,因为DAO层需要捕获异常并在finally中关闭拿到的SqlSession
 9      * 
10      * mybatis的SqlSession也是提供的供数据库的会话,其实是对JDBC的二次封装,因此拿到数据后也是需要关闭的
11      */
12     public SqlSession getSqlSession() throws IOException {
13         //通过配置文件获取数据库连接信息    路径从src根路径下面开始算起
14         Reader reader = Resources.getResourceAsReader("com/imooc/config/Configuration.xml");
15         //通过配置信息构建一个SqlSessionFactory
16         SqlSessionFactory SqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
17         //通过SqlSessionFactory打开一个数据库会话
18         SqlSession sqlSession = SqlSessionFactory.openSession();
19         return sqlSession;
20     }
21 }

public class MessageDao {
    /**
     * 根据查询条件查询消息列表
     * @param command
     * @param description
     * @return
     */
    public List<Message> queryMessageList(String command,String description) {
        DBAccess dbAccess = new DBAccess();
        SqlSession sqlSession = null;
        //通过sqlSession执行SQL语句
        
        try {
            sqlSession = dbAccess.getSqlSession();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            sqlSession.close();
        }
        
        
        return null;
    }
    public static void main(String[] args) {
        MessageDao messageDao = new MessageDao();
        //测试queryMessageList是否能够否文数据库
        messageDao.queryMessageList("test","test");
    }
}

  <mappers>
    <mapper resource="com/imooc/config/sqlxml/Message.xml"/>
  </mappers>

public List<Message> queryMessageList(String command,String description) {
        DBAccess dbAccess = new DBAccess();
        List<Message> messageList = new ArrayList<Message>();
        SqlSession sqlSession = null;
        try {
            Message message = new Message();
            message.setCommand(command);
            message.setDescription(description);
            sqlSession = dbAccess.getSqlSession();
            // 通过sqlSession执行SQL语句
            messageList = sqlSession.selectList("Message.queryMessageList", message);
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } finally {
            if(sqlSession != null) {
                sqlSession.close();
            }
        }
        return messageList;
    }

<select id="queryMessageList" parameterType="com.imooc.bean.Message" resultMap="MessageResult">
    select ID,COMMAND,DESCRIPTION,CONTENT from MESSAGE
    <where>
        <if test="command != null and !&quot;&quot;.equals(command.trim())">
            and COMMAND=#{command}
        </if>
        <if test="description != null and !&quot;&quot;.equals(description.trim())">
            and DESCRIPTION like ‘%‘ #{description} ‘%‘
        </if>
    </where>
  </select>

<if test="description != null and!&quot;&quot;.equals(description.trim())">
    and DESCRIPTION like ‘%‘ #{description} ‘%‘
</if>