日志

1.日志工厂

如果一个数据库的操作，出现了异常，我们需要排错。日志就是最好的工具。

日志工厂：SLF4JLOG4J(掌握）LOG4J2JDK_LOGGINGCOMMONS_LOGGING==STDOUT_LOGGING（掌握）==NO_LOGGING

2.分页

减少数据的处理量

Limit分页

select * from user limit 2,2

从第三个开始，查找两个。如果只有一个参数0~n

使用myBatis实现分页。

1.接口

//分页List<User> getUserByLimit(Map<String,Integer> map);

2.Mapper.xml

<select id="getUserByLimit" parameterType="map" resultType="user">select * from mybatis.user limit #{startIndex},#{pageSize}</select>

3.测试

public void getTest(){SqlSession sqlSession = MybatisUtils.getSqlSession();UserMapper mapper = sqlSession.getMapper(UserMapper.class);HashMap<String, Integer> map = new HashMap<String, Integer>();map.put("startIndex",1);map.put("pageSize",2);List<User> user = mapper.getUserByLimit(map);for (User user1 : user) {System.out.println(user);}sqlSession.close();}

RowBounds分页

1.接口

List<User> getUserByRowBounds();

2.xml文件

<select id="getUserByRowBounds" resultType="user">select * from mybatis.user</select>

3.测试

 public void rowBoundsTest(){SqlSession sqlSession = MybatisUtils.getSqlSession();RowBounds rowBounds = new RowBounds(2, 2);List<User> userList;userList = sqlSession.selectList("dao.UserMapper.getUserByRowBounds",null,rowBounds);for (User user : userList) {System.out.println(user);}sqlSession.close();}

注解开发