【mybatis】 从0开始搭建mybatis、注解开发

• 本篇文章的目的主要是为了熟悉xml配置与注解配置的对应关系。
• 从0开始

搭建环境

pow.xml 导入maven坐标、依赖

• 搭建mybatis的必需品 ：mybatis3、mysql-connector-java
• log4j、junit、lombok

<dependencies>
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.4.5</version>
</dependency>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.11</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
<version>1.2.12</version>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>5.1.30</version>
<scope>runtime</scope>
</dependency>
<dependency>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
<version>1.16.20</version>
</dependency>
</dependencies>

编写实体类

-实现序列化接口

package com.wei.pojo;
public class User implements Serializable {
private Integer id;
private String username;
private Date birthday;
private String sex;
private String address;
}

编写mapper接口

package com.wei.mapper;
public interface UserMapper {
List<User> findAll();
User findUserById(Integer id);
}

映射配置文件（注解开发可不写）

• 如果使用注解开发，那么resource对应路径上（com.xxx.mapper.UserMapper.xml）的xml不能存在。不然会报错。

主配置文件mybatis-config.xml（不可省略）

<?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>
<!-- 加载数据库信息 -->
<properties resource="jdbcConfig.properties"></properties>

<typeAliases>
<package name="com.wei.pojo"/>
</typeAliases>

<environments default="mysql">
<environment id="mysql">
<transactionManager type="JDBC"></transactionManager>
<dataSource type="POOLED">
<property name="driver" value="${jdbc.driver}"/>
<property name="url" value="${jdbc.url}"/>
<property name="username" value="${jdbc.username}"/>
<property name="password" value="${jdbc.password}"/>
</dataSource>
</environment>
</environments>
<!-- 指定带有注解的mapper接口所在位置 -->
<mappers>
<package name="com.wei.mapper" />
</mappers>
</configuration>

需要引入数据库信息 jdbcConfig.properties和LOG4J日志文件log4j.properties

• jdbcConfig.properties

jdbc.driver=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/mybatis
jdbc.username=root
jdbc.password=root

• log4j.properties

#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

log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d %p [%c] - %m%n

#文件输出的相关设置
log4j.appender.file = org.apache.log4j.RollingFileAppender
log4j.appender.file.File=./log/kuang.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

编写sql到mapper接口对应的方法上

• CRUD的四种注解
  @Select、@Insert、@Delete、@Update
• 编写完成，测试程序是否可用运行。

CRUD操作

• 简单的CRUD 无非就是将原本的xml改为把注解写在接口的方法上。

注解查询、多表查询 Results、Result

• 数据库字段与实体类属性不一致

• 使用Results 、Result 完成多表封装.

public interface UserMapper {
@Select("select * from user")
@Results(id="userMap" ,value = {
@Result(id=true,column = "id" , property = "userId"),
@Result(id=false,column = "birthday" , property = "userBirthday"),
@Result(id=false,column = "username" , property = "userName"),
@Result(id=false,column = "sex" , property = "userSex"),
@Result(id=false,column = "address" , property = "userAddress"),
})
List<User> findAll2();
//resultMap 结果映射的复用，即指定id。
@ResultMap("userMap")
@Select("select * from user where id = #{id}")
User findUserById(Integer id);

}

-以下，一对一、一对多的注解知识点对应XML内容
https://blog.csdn.net/qq_30081043/article/details/107581869

注解一对一 one = @one

• 一般情况，一对一使用急切的加载，而一对多使用懒加载。

public interface AccountMapper {
@Select("select * from account")
@Results(id="accountMap" , value = {
@Result(id=true,column = "id" , property = "id"),
@Result(id=false,column = "uid" , property = "uid"),
@Result(id=false,column = "money" , property = "money"),
@Result(id=false,column = "uid" , property = "user",
one = @One(select = "com.wei.mapper.UserMapper.findUserById" , fetchType = FetchType.EAGER) )
})
List<Account> findAll();

@ResultMap("accountMap")
@Select("select * from account where uid = #{id}")
List<Account> findAccountById(Integer id);
}

注解一对多 many = @many

public interface UserMapper {
@Select("select * from user")
@Results(id="userMap" ,value = {
@Result(id=true,column = "id" , property = "userId"),
@Result(id=false,column = "birthday" , property = "userBirthday"),
@Result(id=false,column = "username" , property = "userName"),
@Result(id=false,column = "sex" , property = "userSex"),
@Result(id=false,column = "address" , property = "userAddress"),
@Result(column = "id", property = "accounts" ,
many = @Many(select = "com.wei.mapper.AccountMapper.findAccountById",fetchType = FetchType.LAZY))
})
List<User> findAll2();

//resultMap 结果映射的复用，即指定id。
@ResultMap("userMap")
@Select("select * from user where id = #{id}")
User findUserById(Integer id);
}

注解开发中使用二级缓存

• 在注解中，和XML一样，默认存在一级缓存。
• 同一sqlSessionFactory创建的sqlsession可以使用二级缓存。

• 在mapper接口上添加注解
• @CacheNamespace(blocking = true)
• 即可开启二级缓存

• 对应xml开启二级缓存

<!--配置开启二级缓存，在对应的mapper映射文件添加标签-->
<cache/>

<settings>
<!--默认开启缓存-->
<setting name="cacheEnabled" value="true"/>
</settings>