Mybatis入门

Posted 2020-08-14

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Mybatis

1. Mybatis介绍

MyBatis是支持普通SQL查询，存储过程和高级映射的优秀持久层框架。MyBatis消除了几乎所有的JDBC代码和参数的手工设置以及对结果集的检索封装。MyBatis可以使用简单的XML或注解用于配置和原始映射，将接口和Java的POJO（Plain Old Java Objects，普通的Java对象）映射成数据库中的记录.

JDBC-àdbutils(自动封装)-àMyBatis-àHibernate

2. mybatis快速入门

编写第一个基于mybaits的测试例子:

2.1. 添加jar包

【mybatis】

mybatis-3.1.1.jar

【mysql驱动包】
mysql-connector-java-5.1.7-bin.jar

2.2. 建库+表

create database mybatis;

use mybatis;

CREATE TABLE users(id INT PRIMARY KEY AUTO_INCREMENT, NAME VARCHAR(20), age INT);

INSERT INTO users(NAME, age) VALUES(‘Tom‘, 12);

INSERT INTO users(NAME, age) VALUES(‘Jack‘, 11);

2.3. 添加Mybatis的配置文件conf.xml

<?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">

</dataSource>

</environment>

</environments>

</configuration>

2.4. 定义表所对应的实体类

public class User {

private int id;

private String name;

private int age;

//get,set方法

}

2.5. 定义操作users表的sql映射文件userMapper.xml

<?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">

<select id="getUser" parameterType="int"

resultType="com.atguigu.mybatis_test.test1.User">

select * from users where id=#{id}

</select>

</mapper>

2.6. 在conf.xml文件中注册userMapper.xml文件

</mappers>

2.7. 编写测试代码：执行定义的select语句

public class Test {

public static void main(String[] args) throws IOException {

String resource = "conf.xml";

//加载mybatis的配置文件（它也加载关联的映射文件）

Reader reader = Resources.getResourceAsReader(resource);

//构建sqlSession的工厂

SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(reader);

//创建能执行映射文件中sql的sqlSession

SqlSession session = sessionFactory.openSession();

//映射sql的标识字符串

String statement = "com.atguigu.mybatis.bean.userMapper"+".selectUser";

//执行查询返回一个唯一user对象的sql

User user = session.selectOne(statement, 1);

System.out.println(user);

}

3. 操作users表的CRUD

3.1. XML的实现

1). 定义sql映射xml文件：

insert into users(name, age) values(#{name}, #{age});

</insert>

delete from users where id=#{id}

</delete>

update users set name=#{name},age=#{age} where id=#{id}

</update>

select * from users where id=#{id}

</select>

select * from users

</select>

2). 在config.xml中注册这个映射文件

3). 在dao中调用：

public User getUserById(int id) {

SqlSession session = sessionFactory.openSession();

User user = session.selectOne(URI+".selectUser", id);

return user;

}

3.2. 注解的实现

1). 定义sql映射的接口

public interface UserMapper {

@Insert("insert into users(name, age) values(#{name}, #{age})")

public int insertUser(User user);

@Delete("delete from users where id=#{id}")

public int deleteUserById(int id);

@Update("update users set name=#{name},age=#{age} where id=#{id}")

public int updateUser(User user);

@Select("select * from users where id=#{id}")

public User getUserById(int id);

@Select("select * from users")

public List<User> getAllUser();

}

2). 在config中注册这个映射接口

3). 在dao类中调用

public User getUserById(int id) {

SqlSession session = sessionFactory.openSession();

UserMapper mapper = session.getMapper(UserMapper.class);

User user = mapper.getUserById(id);

return user;

}

4. 几个可以优化的地方

4.1. 连接数据库的配置单独放在一个properties文件中

## db.properties

4.2. 为实体类定义别名,简化sql映射xml文件中的引用

</typeAliases>

4.3. 可以在src下加入log4j的配置文件,打印日志信息

1. 添加jar:

log4j-1.2.16.jar

2.1. log4j.properties(方式一)

log4j.properties，

log4j.rootLogger=DEBUG, Console

#Console

log4j.appender.Console=org.apache.log4j.ConsoleAppender

log4j.appender.Console.layout=org.apache.log4j.PatternLayout

log4j.appender.Console.layout.ConversionPattern=%d [%t] %-5p [%c] - %m%n

log4j.logger.java.sql.ResultSet=INFO

log4j.logger.org.apache=INFO

log4j.logger.java.sql.Connection=DEBUG

log4j.logger.java.sql.Statement=DEBUG

log4j.logger.java.sql.PreparedStatement=DEBUG

2.2. log4j.xml(方式二)

<?xml version="1.0" encoding="UTF-8" ?>

<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">

<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">

<param name="ConversionPattern"

value="%-5p %d{MM-dd HH:mm:ss,SSS} %m (%F:%L) \n" />

</layout>

</appender>

</logger>

</logger>

<root>

<appender-ref ref="STDOUT" />

</root>

</log4j:configuration>

5. 解决字段名与实体类属性名不相同的冲突

5.1. 准备表和数据：

CREATE TABLE orders(

order_id INT PRIMARY KEY AUTO_INCREMENT,

order_no VARCHAR(20),

order_price FLOAT

);

INSERT INTO orders(order_no, order_price) VALUES(‘aaaa‘, 23);

INSERT INTO orders(order_no, order_price) VALUES(‘bbbb‘, 33);

INSERT INTO orders(order_no, order_price) VALUES(‘cccc‘, 22);

5.2. 定义实体类：

public class Order {

private int id;

private String orderNo;

private float price;

}

5.3. 实现getOrderById(id)的查询：

方式一: 通过在sql语句中定义别名

select order_id id, order_no orderNo,order_price price from orders where order_id=#{id}

</select>

方式二: 通过<resultMap>

select * from orders where order_id=#{id}

</select>

<resultMap type="_Order" id="orderResultMap">

</resultMap>

6.实现关联表查询

6.1. 一对一关联

1). 提出需求

根据班级id查询班级信息(带老师的信息)

2). 创建表和数据

CREATE TABLE teacher(

t_id INT PRIMARY KEY AUTO_INCREMENT,

t_name VARCHAR(20)

);

CREATE TABLE class(

c_id INT PRIMARY KEY AUTO_INCREMENT,

c_name VARCHAR(20),

teacher_id INT

);

ALTER TABLE class ADD CONSTRAINT fk_teacher_id FOREIGN KEY (teacher_id) REFERENCES teacher(t_id);

INSERT INTO teacher(t_name) VALUES(‘LS1‘);

INSERT INTO teacher(t_name) VALUES(‘LS2‘);

INSERT INTO class(c_name, teacher_id) VALUES(‘bj_a‘, 1);

INSERT INTO class(c_name, teacher_id) VALUES(‘bj_b‘, 2);

3). 定义实体类：

public class Teacher {

private int id;

private String name;

}

public class Classes {

private int id;

private String name;

private Teacher teacher;

}

4). 定义sql映射文件ClassMapper.xml

<!--

方式一：嵌套结果：使用嵌套结果映射来处理重复的联合结果的子集

封装联表查询的数据(去除重复的数据)

select * from class c, teacher t where c.teacher_id=t.t_id and c.c_id=1

-->

select * from class c, teacher t where c.teacher_id=t.t_id and c.c_id=#{id}

</select>

<association property="teacher" javaType="_Teacher">

</association>

</resultMap>

<!--

方式二：嵌套查询：通过执行另外一个SQL映射语句来返回预期的复杂类型

SELECT * FROM class WHERE c_id=1;

SELECT * FROM teacher WHERE t_id=1 //1 是上一个查询得到的teacher_id的值

-->

select * from class where c_id=#{id}

</select>

</association>

</resultMap>

SELECT t_id id, t_name name FROM teacher WHERE t_id=#{id}

</select>

5). 测试

@Test

public void testOO() {

SqlSession sqlSession = factory.openSession();

Classes c = sqlSession.selectOne("com.atguigu.day03_mybatis.test5.OOMapper.getClass", 1);

System.out.println(c);

}

@Test

public void testOO2() {

SqlSession sqlSession = factory.openSession();

Classes c = sqlSession.selectOne("com.atguigu.day03_mybatis.test5.OOMapper.getClass2", 1);

System.out.println(c);

}

6.2. 一对多关联

1). 提出需求

根据classId查询对应的班级信息,包括学生,老师

2). 创建表和数据：

CREATE TABLE student(

s_id INT PRIMARY KEY AUTO_INCREMENT,

s_name VARCHAR(20),

class_id INT

);

INSERT INTO student(s_name, class_id) VALUES(‘xs_A‘, 1);

INSERT INTO student(s_name, class_id) VALUES(‘xs_B‘, 1);

INSERT INTO student(s_name, class_id) VALUES(‘xs_C‘, 1);

INSERT INTO student(s_name, class_id) VALUES(‘xs_D‘, 2);

INSERT INTO student(s_name, class_id) VALUES(‘xs_E‘, 2);

INSERT INTO student(s_name, class_id) VALUES(‘xs_F‘, 2);

3). 定义实体类：

public class Student {

private int id;

private String name;

}

public class Classes {

private int id;

private String name;

private Teacher teacher;

private List<Student> students;

}

4). 定义sql映射文件ClassMapper.xml

<!--

方式一: 嵌套结果: 使用嵌套结果映射来处理重复的联合结果的子集

SELECT * FROM class c, teacher t,student s WHERE c.teacher_id=t.t_id AND c.C_id=s.class_id AND c.c_id=1

-->

select * from class c, teacher t,student s where c.teacher_id=t.t_id and c.C_id=s.class_id and c.c_id=#{id}

</select>

</association>

<collection property="students" ofType="_Student">

</collection>

</resultMap>

<!--

方式二：嵌套查询：通过执行另外一个SQL映射语句来返回预期的复杂类型

SELECT * FROM class WHERE c_id=1;

SELECT * FROM teacher WHERE t_id=1 //1 是上一个查询得到的teacher_id的值

SELECT * FROM student WHERE class_id=1 //1是第一个查询得到的c_id字段的值

-->

select * from class where c_id=#{id}

</select>

<collection property="students" ofType="_Student" column="c_id" select="getStudent"></collection>

</resultMap>

SELECT t_id id, t_name name FROM teacher WHERE t_id=#{id}

</select>

SELECT s_id id, s_name name FROM student WHERE class_id=#{id}

</select>

5). 测试：

@Test

public void testOM() {

SqlSession sqlSession = factory.openSession();

Classes c = sqlSession.selectOne("com.atguigu.day03_mybatis.test5.OOMapper.getClass3", 1);

System.out.println(c);

}

@Test

public void testOM2() {

SqlSession sqlSession = factory.openSession();

Classes c = sqlSession.selectOne("com.atguigu.day03_mybatis.test5.OOMapper.getClass4", 1);

System.out.println(c);

}

7. 动态SQL与模糊查询

7.1. 提出需求:

实现多条件查询用户(姓名模糊匹配, 年龄在指定的最小值到最大值之间)

7.2. 准备数据表和数据:

create table d_user(

id int primary key auto_increment,

name varchar(10),

age int(3)

);

insert into d_user(name,age) values(‘Tom‘,12);

insert into d_user(name,age) values(‘Bob‘,13);

insert into d_user(name,age) values(‘Jack‘,18);

7.3. ConditionUser(查询条件实体类)

private String name;

private int minAge;

private int maxAge;

7.4. User(表实体类)

private int id;

private String name;

private int age;

7.5. userMapper.xml(映射文件)

<?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">

select * from d_user where age>=#{minAge} and age<=#{maxAge}

</select>

</mapper>

7.6. UserTest(测试)

public class UserTest {

public static void main(String[] args) throws IOException {

Reader reader = Resources.getResourceAsReader("conf.xml");

SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(reader);

SqlSession sqlSession = sessionFactory.openSession();

String statement = "com.atguigu.day03_mybatis.test6.userMapper.getUser";

List<User> list = sqlSession.selectList(statement, new ConditionUser("%a%", 1, 12));

System.out.println(list);

}

MyBatis中可用的动态SQL标签

8.调用存储过程

8.1. 提出需求:

查询得到男性或女性的数量, 如果传入的是0就女性否则是男性

8.2. 准备数据库表和存储过程:

create table p_user(

id int primary key auto_increment,

name varchar(10),

sex char(2)

);

insert into p_user(name,sex) values(‘A‘,"男");

insert into p_user(name,sex) values(‘B‘,"女");

insert into p_user(name,sex) values(‘C‘,"男");

#创建存储过程(查询得到男性或女性的数量, 如果传入的是0就女性否则是男性)

DELIMITER $

CREATE PROCEDURE mybatis.ges_user_count(IN sex_id INT, OUT user_count INT)

BEGIN

IF sex_id=0 THEN

SELECT COUNT(*) FROM mybatis.p_user WHERE p_user.sex=‘女‘ INTO user_count;

ELSE

SELECT COUNT(*) FROM mybatis.p_user WHERE p_user.sex=‘男‘ INTO user_count;

END IF;

END

#调用存储过程

DELIMITER ;

SET @user_count = 0;

CALL mybatis.ges_user_count(1, @user_count);

SELECT @user_count;

8.3. 创建表的实体类

public class User {

private String id;

private String name;

private String sex;

}

8.4. userMapper.xml

<!--

查询得到男性或女性的数量, 如果传入的是0就女性否则是男性

CALL mybatis.get_user_count(1, @user_count);

-->

call mybatis.get_user_count(?,?)

</select>

</parameterMap>

</mapper>

8.5. 测试调用:

Map<String, Integer> paramMap = new HashMap<>();

paramMap.put("sex_id", 0);

session.selectOne(statement, paramMap);

Integer userCount = paramMap.get("user_count");

System.out.println(userCount);

9. Mybatis缓存

9.1. 理解MyBatis缓存

正如大多数持久层框架一样，MyBatis 同样提供了一级缓存和二级缓存的支持

一级缓存: 基于PerpetualCache 的 HashMap本地缓存，其存储作用域为 Session，当 Session flush 或 close 之后，该Session中的所有 Cache 就将清空。

2. 二级缓存与一级缓存其机制相同，默认也是采用 PerpetualCache，HashMap存储，不同在于其存储作用域为 Mapper(Namespace)，并且可自定义存储源，如 Ehcache。

3. 对于缓存数据更新机制，当某一个作用域(一级缓存Session/二级缓存Namespaces)的进行了 C/U/D 操作后，默认该作用域下所有 select 中的缓存将被clear。

9.2. Mybatis一级缓存

1) 提出需求:

根据id查询对应的用户记录对象

2). 准备数据库表和数据

CREATE TABLE c_user(

id INT PRIMARY KEY AUTO_INCREMENT,

NAME VARCHAR(20),

age INT

);

INSERT INTO c_user(NAME, age) VALUES(‘Tom‘, 12);

INSERT INTO c_user(NAME, age) VALUES(‘Jack‘, 11);

3). 创建表的实体类

public class User implements Serializable{

private int id;

private String name;

private int age;

}

4). userMapper.xml

<?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">

select * from c_user where id=#{id}

</select>

update c_user set

name=#{name}, age=#{age} where id=#{id}

</update>

</mapper>

5). 测试:

* 一级缓存: 也就Session级的缓存(默认开启)

@Test

public void testCache1() {

SqlSession session = MybatisUtils.getSession();

String statement = "com.atguigu.mybatis.test8.userMapper.getUser";

User user = session.selectOne(statement, 1);

System.out.println(user);

* 一级缓存默认就会被使用

user = session.selectOne(statement, 1);

System.out.println(user);

1. 必须是同一个Session,如果session对象已经close()过了就不可能用了

session = MybatisUtils.getSession();

user = session.selectOne(statement, 1);

System.out.println(user);

2. 查询条件是一样的

user = session.selectOne(statement, 2);

System.out.println(user);

3. 没有执行过session.clearCache()清理缓存

session.clearCache();

user = session.selectOne(statement, 2);

System.out.println(user);

4. 没有执行过增删改的操作(这些操作都会清理缓存)

session.update("com.atguigu.mybatis.test8.userMapper.updateUser",

new User(2, "user", 23));

user = session.selectOne(statement, 2);

System.out.println(user);

}

9.3. Mybatis二级缓存

1). 添加一个<cache>在userMapper.xml中

<cache/>

2). 测试

* 测试二级缓存

@Test

public void testCache2() {

String statement = "com.atguigu.mybatis.test8.userMapper.getUser";

SqlSession session = MybatisUtils.getSession();

User user = session.selectOne(statement, 1);

session.commit();

System.out.println("user="+user);

SqlSession session2 = MybatisUtils.getSession();

user = session2.selectOne(statement, 1);

session.commit();

System.out.println("user2="+user);

}

3). 补充说明

1. 映射语句文件中的所有select语句将会被缓存。

2. 映射语句文件中的所有insert，update和delete语句会刷新缓存。

3. 缓存会使用Least Recently Used（LRU，最近最少使用的）算法来收回。

4. 缓存会根据指定的时间间隔来刷新。

5. 缓存会存储1024个对象

<cache

eviction="FIFO" //回收策略为先进先出

flushInterval="60000" //自动刷新时间60s

size="512" //最多缓存512个引用对象

readOnly="true"/> //只读

10. spring集成mybatis

10.1. 添加Jar包

【mybatis】

mybatis-3.2.0.jar

mybatis-spring-1.1.1.jar

log4j-1.2.17.jar

【spring】

spring-aop-3.2.0.RELEASE.jar

spring-beans-3.2.0.RELEASE.jar

spring-context-3.2.0.RELEASE.jar

spring-core-3.2.0.RELEASE.jar

spring-expression-3.2.0.RELEASE.jar

spring-jdbc-3.2.0.RELEASE.jar

spring-test-3.2.4.RELEASE.jar

spring-tx-3.2.0.RELEASE.jar

aopalliance-1.0.jar

cglib-nodep-2.2.3.jar

commons-logging-1.1.1.jar

【MYSQL驱动包】

mysql-connector-java-5.0.4-bin.jar

10.2. 数据库表

CREATE TABLE s_user(

user_id INT AUTO_INCREMENT PRIMARY KEY,

user_name VARCHAR(30),

user_birthday DATE,

user_salary DOUBLE

)

10.3. 实体类: User

public class User {

private int id;

private String name;

private Date birthday;

private double salary;

//set,get方法

}

10.4. DAO接口: UserMapper (XXXMapper)

public interface UserMapper {

void save(User user);

void update(User user);

void delete(int id);

User findById(int id);

List<User> findAll();

}

10.5. SQL映射文件: userMapper.xml(与接口忽略大小写同名)

<?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">

</resultMap>

insert into s_user(user_name,user_birthday,user_salary)

values(#{name},#{birthday},#{salary})

</insert>

update s_user

set user_name = #{name},

user_birthday = #{birthday},

user_salary = #{salary}

where user_id = #{id}

</update>

delete from s_user

where user_id = #{id}

</delete>

select *

from s_user

where user_id = #{id}

</select>

select *

from s_user

</select>

</mapper>

10.6. spring的配置文件: beans.xml

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns:p="http://www.springframework.org/schema/p"

xmlns:context="http://www.springframework.org/schema/context"

xmlns:tx="http://www.springframework.org/schema/tx"

xsi:schemaLocation="

http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans-3.2.xsd

http://www.springframework.org/schema/context

http://www.springframework.org/schema/context/spring-context-3.2.xsd

http://www.springframework.org/schema/tx

http://www.springframework.org/schema/tx/spring-tx-3.2.xsd">

<bean id="dataSource"

class="org.springframework.jdbc.datasource.DriverManagerDataSource">

</bean>

<!--

2. mybatis的SqlSession的工厂: SqlSessionFactoryBean

dataSource / typeAliasesPackage

-->

</bean>

<!--

3. mybatis自动扫描加载Sql映射文件 : MapperScannerConfigurer

sqlSessionFactory / basePackage

-->

</bean>

</bean>

<tx:annotation-driven transaction-manager="txManager" />

</beans>

10.7. mybatis的配置文件: mybatis-config.xml

<?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>

10.8. 测试

@RunWith(SpringJUnit4ClassRunner.class) //使用Springtest测试框架

@ContextConfiguration("/beans.xml") //加载配置

public class SMTest {

@Autowired //注入

private UserMapper userMapper;

@Test

public void save() {

User user = new User();

user.setBirthday(new Date());

user.setName("marry");

user.setSalary(300);

userMapper.save(user);

System.out.println(user.getId());

}

@Test

public void update() {

User user = userMapper.findById(2);

user.setSalary(2000);

userMapper.update(user);

}

@Test

public void delete() {

userMapper.delete(3);

}

@Test

public void findById() {

User user = userMapper.findById(1);

System.out.println(user);

}

@Test

public void findAll() {

List<User> users = userMapper.findAll();

System.out.println(users);

}

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