MyBatis（二）

发表于 2021-02-09 更新于 2024-01-18 阅读次数：本文字数： 2.1k 阅读时长 ≈ 8 分钟

因为内容太多了，所以将其拆分为以下内容

参考

https://www.bilibili.com/video/BV1NE411Q7Nx

https://mybatis.org/mybatis-3/zh/index.html

日志

日志工厂

设置名	描述	有效值	默认值
logImpl	指定 MyBatis 所用日志的具体实现，未指定时将自动查找。	SLF4J \| LOG4J \| LOG4J2 \| JDK_LOGGING \| COMMONS_LOGGING \| STDOUT_LOGGING \| NO_LOGGING	未设置

Mybatis 通过使用内置的日志工厂提供日志功能。内置日志工厂将会把日志工作委托给下面的实现之一：

SLF4J
Apache Commons Logging
Log4j 2
Log4j
JDK logging

配置日志

核心配置加入

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

测试结果：

initialized using 'class org.apache.ibatis.logging.stdout.StdOutImpl' adapter.

PooledDataSource forcefully closed/removed all connections.
PooledDataSource forcefully closed/removed all connections.
PooledDataSource forcefully closed/removed all connections.
PooledDataSource forcefully closed/removed all connections.
Opening JDBC Connection
Created connection 1658699134.
Setting autocommit to false on JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@62ddbd7e]
==>  Preparing: select * from user where id = ? 
==> Parameters: 1(Integer)
<==    Columns: id, name, pwd
<==        Row: 1, 张三, 123456
<==      Total: 1
User0{id=1, name='张三', password='123456'}
Resetting autocommit to true on JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@62ddbd7e]
Closing JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@62ddbd7e]
Returned connection 1658699134 to pool.
Process finished with exit code 0

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，甚至是套接口服务器、NT的事件记录器、UNIX Syslog 守护进程等；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。最令人感兴趣的就是，这些可以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。

1、导入 log4j 包

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

2、log4j.properties

详细配置

# priority  :debug<info<warn<error
#you cannot specify every priority with different file for log4j 
log4j.rootLogger=debug,stdout,info,debug,warn,error 
 
#console
log4j.appender.stdout=org.apache.log4j.ConsoleAppender 
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout 
log4j.appender.stdout.layout.ConversionPattern= [%d{yyyy-MM-dd HH:mm:ss a}]:%p %l%m%n
#info log
log4j.logger.info=info
log4j.appender.info=org.apache.log4j.DailyRollingFileAppender 
log4j.appender.info.DatePattern='_'yyyy-MM-dd'.log'
log4j.appender.info.File=./src/com/hp/log/info.log
log4j.appender.info.Append=true
log4j.appender.info.Threshold=INFO
log4j.appender.info.layout=org.apache.log4j.PatternLayout 
log4j.appender.info.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss a} [Thread: %t][ Class:%c >> Method: %l ]%n%p:%m%n
#debug log
log4j.logger.debug=debug
log4j.appender.debug=org.apache.log4j.DailyRollingFileAppender 
log4j.appender.debug.DatePattern='_'yyyy-MM-dd'.log'
log4j.appender.debug.File=./src/com/hp/log/debug.log
log4j.appender.debug.Append=true
log4j.appender.debug.Threshold=DEBUG
log4j.appender.debug.layout=org.apache.log4j.PatternLayout 
log4j.appender.debug.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss a} [Thread: %t][ Class:%c >> Method: %l ]%n%p:%m%n
#warn log
log4j.logger.warn=warn
log4j.appender.warn=org.apache.log4j.DailyRollingFileAppender 
log4j.appender.warn.DatePattern='_'yyyy-MM-dd'.log'
log4j.appender.warn.File=./src/com/hp/log/warn.log
log4j.appender.warn.Append=true
log4j.appender.warn.Threshold=WARN
log4j.appender.warn.layout=org.apache.log4j.PatternLayout 
log4j.appender.warn.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss a} [Thread: %t][ Class:%c >> Method: %l ]%n%p:%m%n
#error
log4j.logger.error=error
log4j.appender.error = org.apache.log4j.DailyRollingFileAppender
log4j.appender.error.DatePattern='_'yyyy-MM-dd'.log'
log4j.appender.error.File = ./src/com/hp/log/error.log 
log4j.appender.error.Append = true
log4j.appender.error.Threshold = ERROR 
log4j.appender.error.layout = org.apache.log4j.PatternLayout
log4j.appender.error.layout.ConversionPattern = %d{yyyy-MM-dd HH:mm:ss a} [Thread: %t][ Class:%c >> Method: %l ]%n%p:%m%n

略简版

#将等级为DEBUG的日志信息输出到console和file这两个目的地，console和file的定义在下面的代码
log4j.rootLogger=DEBUG,console,file

#控制台输出的相关设置
log4j.appender.console = org.apache.log4j.ConsoleAppender
log4j.appender.console.Target = System.out
log4j.appender.console.Threshold=DEBUG
log4j.appender.console.layout = org.apache.log4j.PatternLayout
log4j.appender.console.layout.ConversionPattern=[%c]-%m%n

#文件输出的相关设置
log4j.appender.file = org.apache.log4j.RollingFileAppender
log4j.appender.file.File=./log/wnhyang.log
log4j.appender.file.MaxFileSize=10mb
log4j.appender.file.Threshold=DEBUG
log4j.appender.file.layout=org.apache.log4j.PatternLayout
log4j.appender.file.layout.ConversionPattern=[%p][%d{yy-MM-dd}][%c]%m%n

#日志输出级别
log4j.logger.org.mybatis=DEBUG
log4j.logger.java.sql=DEBUG
log4j.logger.java.sql.Statement=DEBUG
log4j.logger.java.sql.ResultSet=DEBUG
log4j.logger.java.sql.PreparedStatement=DEBUG

极简版

# 全局日志配置
log4j.rootLogger=ERROR,stdout
# MyBatis 日志配置
log4j.logger.org.mybatis.example.BlogMapper=TRACE
# 控制台输出
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%5p [%t] - %m%n

3、配置 log4j

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

4、测试运行

[org.apache.ibatis.logging.LogFactory]-Logging initialized using 'class org.apache.ibatis.logging.log4j.Log4jImpl' adapter.
[org.apache.ibatis.datasource.pooled.PooledDataSource]-PooledDataSource forcefully closed/removed all connections.
[org.apache.ibatis.datasource.pooled.PooledDataSource]-PooledDataSource forcefully closed/removed all connections.
[org.apache.ibatis.datasource.pooled.PooledDataSource]-PooledDataSource forcefully closed/removed all connections.
[org.apache.ibatis.datasource.pooled.PooledDataSource]-PooledDataSource forcefully closed/removed all connections.
[org.apache.ibatis.transaction.jdbc.JdbcTransaction]-Opening JDBC Connection
[org.apache.ibatis.datasource.pooled.PooledDataSource]-Created connection 279593458.
[org.apache.ibatis.transaction.jdbc.JdbcTransaction]-Setting autocommit to false on JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@10aa41f2]
[com.dao.UserMapper.getUserById]-==>  Preparing: select * from user where id = ? 
[com.dao.UserMapper.getUserById]-==> Parameters: 1(Integer)
[com.dao.UserMapper.getUserById]-<==      Total: 1
User0{id=1, name='张三', password='123456'}
[org.apache.ibatis.transaction.jdbc.JdbcTransaction]-Resetting autocommit to true on JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@10aa41f2]
[org.apache.ibatis.transaction.jdbc.JdbcTransaction]-Closing JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@10aa41f2]
[org.apache.ibatis.datasource.pooled.PooledDataSource]-Returned connection 279593458 to pool.

简单使用：

1、在要使用 Log4j 的类中，导入包 import org.apache.log4j.Logger;

2、日志对象，参数为当前的class

1	static Logger logger= Logger.getLogger(UserDaoTest.class);

3、日志级别

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logger.info("info：进入了testLog4j");
logger.debug("debug：进入了testLog4j");
logger.error("error：进入了testLog4j");

注解开发

使用注解来映射简单语句会使代码显得更加简洁，但对于稍微复杂一点的语句，Java 注解不仅力不从心，还会让你本就复杂的 SQL 语句更加混乱不堪。因此，如果你需要做一些很复杂的操作，最好用 XML 来映射语句。

1、接口方法上加上注解

1 2	@Select("select * from user") List<User> getUserList();

2、核心配置绑定接口

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<mappers>
    <mapper resource="com/dao/UserMapper.class"/>
</mappers>

xml 与注解同时使用需要：接口和它的 Mapper 配置文件必须同名且必须在同一包下，并配置 xml

3、测试

本质：反射机制实现

底层：动态代理

CRUD

@Select()
...
@Insert()
...
@Update()
....
@Delete()
...

关于 @Param() 注解

8基本类型 + String 类型，需要加上
引用类型不用加
只有一个基本类型，可以忽略，但建议加上
在 sql 中引用的就是我们这里的 @Param() 中设定的属性名

#{} ${} 区别

参考：

MyBatis视频教程

[#{}与${}的区别](https://blog.csdn.net/qian_qian_123/article/details/92844194?ops_request_misc=%25257B%252522request%25255Fid%252522%25253A%252522160759025519726885835134%252522%25252C%252522scm%252522%25253A%25252220140713.130102334..%252522%25257D&request_id=160759025519726885835134&biz_id=0&utm_medium=distribute.pc_search_result.none-task-blog-2~all~baidu_landing_v2~default-3-92844194.pc_search_result_no_baidu_js&utm_term=#{}%E4%B8%8E${}%E5%8C%BA%E5%88%AB)

Mybatis 详细执行流程

参考

复杂查询

数据库准备

CREATE TABLE `teacher` (
  `id` INT(10) NOT NULL,
  `name` VARCHAR(30) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=INNODB DEFAULT CHARSET=utf8

INSERT INTO teacher(`id`, `name`) VALUES (1, '老杨'); 

CREATE TABLE `student` (
  `id` INT(10) NOT NULL,
  `name` VARCHAR(30) DEFAULT NULL,
  `tid` INT(10) DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `fktid` (`tid`),
  CONSTRAINT `fktid` FOREIGN KEY (`tid`) REFERENCES `teacher` (`id`)
) ENGINE=INNODB DEFAULT CHARSET=utf8
INSERT INTO `student` (`id`, `name`, `tid`) VALUES ('1', '小明', '1'); 
INSERT INTO `student` (`id`, `name`, `tid`) VALUES ('2', '小红', '1'); 
INSERT INTO `student` (`id`, `name`, `tid`) VALUES ('3', '小张', '1'); 
INSERT INTO `student` (`id`, `name`, `tid`) VALUES ('4', '小李', '1'); 
INSERT INTO `student` (`id`, `name`, `tid`) VALUES ('5', '小王', '1');

配置

实体类（使用了 Lombok 插件）

Teacher

@Data
@NoArgsConstructor
@AllArgsConstructor
public class Teacher {
    private int id;
    private String name;
}

Student

@Data
@NoArgsConstructor
@AllArgsConstructor
public class Student {
    private int id;
    private String name;
    private Teacher teacher;
}

接口和对应的 Mapper.xml

注意放在同一包下，且命名相同，如下模板

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.dao.xxxMapper">


</mapper>

核心配置

如果需要的话修改 db.properties

mybatis-config.xml 修改

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <properties resource="db.properties"/> <!-- 数据库配置要正确 -->
    
    <settings> <!-- 自带日志开启 -->
        <setting name="logImpl" value="STDOUT_LOGGING"/>
    </settings>

    <typeAliases> <!-- 扫描包取别名 -->
        <package name="com.pojo"/>
    </typeAliases>
    
    <environments default="development"> <!-- 需要的修改 -->
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="${driver}"/>
                <property name="url" value="${url}"/>
                <property name="username" value="${username}"/>
                <property name="password" value="${password}"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="com/dao/UserMapper.xml"/>
        <mapper resource="com/dao/TeacherMapper.xml"/> <!-- + -->
        <mapper resource="com/dao/StudentMapper.xml"/> <!-- + -->
    </mappers>

</configuration>

测试

要求一：

查询所有学生信息，内容包括（学生id，学生name，老师name）

方法一：

<resultMap id="studentMap" type="Student">
    <result column="id" property="id"/>
    <result column="name" property="name"/>
    <!-- 复杂属性，需要单独处理
         对象：association
         集合：collection
    -->
    <association property="teacher" column="tid" javaType="teacher" select="getTeacherById"/>
</resultMap>


<select id="getStudent" resultMap="studentMap">
    select *
    from student
</select>

<select id="getTeacherById" resultType="teacher">
    select *
    from teacher
    where id = #{id}
</select>

按照查询嵌套处理，相当于子查询

方法二：

<resultMap id="studentMap0" type="Student">
    <result column="sid" property="id"/>
    <result column="sname" property="name"/>
    <!-- 复杂属性，需要单独处理
         对象：association
         集合：collection
    -->
    <association property="teacher" javaType="teacher">
        <result column="tname" property="name" />
    </association>
</resultMap>

<select id="getStudent0" resultMap="studentMap0">
    select s.id sid, s.name sname, t.name tname
    from student s,
         teacher t
    where s.tid = t.id
</select>

按照结果嵌套处理，即连表查询

要求二：

查询所有老师信息，内容包括（老师id，老师name，所有学生（学生id，学生name，学生老师id））

实体类的变化

Student0

@Data
@NoArgsConstructor
@AllArgsConstructor
public class Student0 {
    private int id;
    private String name;
    private int tid;
}

Teacher0

@Data
@NoArgsConstructor
@AllArgsConstructor
public class Teacher0 {
    private int id;
    private String name;
    private List<Student0> student0s;
}

方法一：

<resultMap id="teacherMap0" type="teacher0">
    <result column="id" property="id"/>
    <result column="name" property="name"/>
    <collection property="student0s" javaType="ArrayList" ofType="Student0" select="getStudentByTid" column="id"/>
</resultMap>


<select id="getTeacher0" resultMap="teacherMap0">
    select *
    from teacher
    where id = #{id}
</select>
<select id="getStudentByTid" resultType="student0">
    select *
    from student
    where tid = #{id}
</select>

按照查询嵌套处理，相当于子查询

方法二：

<resultMap id="teacherMap" type="teacher0">
    <result column="tid" property="id"/>
    <result column="tname" property="name"/>
    <!--
        javaType="" 指定属性类型
        集合中的泛型信息，我们使用 ofType 获取
    -->
    <collection property="student0s" ofType="Student0">
        <result property="id" column="sid"/>
        <result property="name" column="sname"/>
        <result property="tid" column="tid"/>
    </collection>
</resultMap>

<select id="getTeacher" resultMap="teacherMap">
    select t.id tid, t.name tname, s.id sid, s.name sname
    from student s,
         teacher t
    where s.tid = t.id
      and t.id = #{id}
</select>

按照结果嵌套处理，即连表查询

总结

1、关联 - association

2、集合 - collection

3、javaType & ofType

javaType 用来指定实体类中属性的类型
ofType 用来指定映射到 List 或集合中的 pojo 类型，泛型中的约束类型

注意点：

sql 可读性
数据库字段与实体类属性对应
排错依靠日志信息（log4j等）

因为内容太多了，所以将其拆分为以下内容