resultMap，日志，分页

转载

mob604756edad5f 2021-08-16 19:23:00

问题：属性名和字段名不一致

解决方法

起别名

select id, username, password as pwd from db4.user

resultMap结果集映射

id username password  数据库----cloumn
id username pwd       实体类----property

UserMapper.xml

<resultMap id="UserMap" type="User">
    <result column="id" property="id"/>
    <result column="username" property="username"/>
    <result column="password" property="pwd"/>
</resultMap>

<select id="getUserList" resultMap="UserMap">
    select id, username, password
    from db4.user
</select>

日志

日志工厂

mybatis-config.xml

<settings>
    <setting name="logImpl" value="STDOUT_LOGGING"/>
</settings>

resultMap，日志，分页_sql

Log4j

Log4j是Apache的一个开源项目，通过使用Log4j，我们可以控制日志信息输送的目的地是控制台、文件、GUI组件
我们也可以控制每一条日志的输出格式;
通过定义每一条日志信息的级别，我们能够更加细致地控制日志的生成过程
通过一个配置文件来灵活地进行配置，而不需要修改应用的代码。

使用

导包

<dependency>
    <groupId>log4j</groupId>
    <artifactId>log4j</artifactId>
    <version>1.2.17</version>
</dependency>

log4j.properties

### 设置###
log4j.rootLogger = debug,stdout,D,E

### 输出信息到控制抬 ###
log4j.appender.stdout = org.apache.log4j.ConsoleAppender
log4j.appender.stdout.Target = System.out
log4j.appender.stdout.layout = org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern = [%-5p] %d{yyyy-MM-dd HH:mm:ss,SSS} method:%l%n%m%n

### 输出DEBUG 级别以上的日志到=./logs/log.log
log4j.appender.D = org.apache.log4j.DailyRollingFileAppender
log4j.appender.D.File = ./logs/log.log
log4j.appender.D.Append = true
log4j.appender.D.Threshold = DEBUG 
log4j.appender.D.layout = org.apache.log4j.PatternLayout
log4j.appender.D.layout.ConversionPattern = %-d{yyyy-MM-dd HH:mm:ss}  [ %t:%r ] - [ %p ]  %m%n

### 输出ERROR 级别以上的日志到=./logs/error.log
log4j.appender.E = org.apache.log4j.DailyRollingFileAppender
log4j.appender.E.File =./logs/error.log 
log4j.appender.E.Append = true
log4j.appender.E.Threshold = ERROR 
log4j.appender.E.layout = org.apache.log4j.PatternLayout
log4j.appender.E.layout.ConversionPattern = %-d{yyyy-MM-dd HH:mm:ss}  [ %t:%r ] - [ %p ]  %m%n

配置log4j为日志的实现mybatis-config.xml

<settings>
    <setting name="logImpl" value="LOG4J"/>
</settings>

简单使用

在要使用Log4j的类中，导入包import org.apache.log4j.Logger;
日志对象，参数为当前类的class

private static Logger logger = Logger.getLogger(test.class);

测试

public class test {
    private static Logger logger = Logger.getLogger(test.class);

    @Test
    public void testLog4j() {
        //日志级别
        logger.debug("This is debug message.");
        // 记录info级别的信息
        logger.info("This is info message.");
        // 记录error级别的信息
        logger.error("This is error message.");
    }
}

分页

使用Limit分页

SELECT * from user limit startIndex , pageSize;

使用mybatis实现分页，核心SQL

接口UserMapper.java

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

Mapper.xml

<select id="getUserByLimit" parameterType="map" resultMap="UserMap">
    SELECT *
    FROM db4.user limit #{startIndex},#{pageSize}
</select>

测试

@Test
public void getUserByLimit_test() {
    SqlSession sqlSession = MybatisUtils.getSqlSession();
    UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
    HashMap<String, Integer> map = new HashMap<>();
    map.put("startIndex", 0);
    map.put("pageSize", 2);
    List<User> userList = userMapper.getUserByLimit(map);
    for (User user : userList) {
        System.out.println(user);
    }
    sqlSession.commit();
    sqlSession.close();
}