MyBatis快速入门(简明浅析易懂)

一、MyBatis简介

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 -> dbutils(自动封装) -> MyBatis -> Hibernate

mybatis是将sql写在xml中，然后去访问数据库。

二、MyBatis快速入门

2.1.新建java项目

　　添加mybatis和mysql的驱动jar：mybatis-3.1.1.jar,mysql-connector-java-5.1.7-bin.jar

2.2.新建表

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

2.4.定义表对应的实体类

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

select * from users where id=#{id}

2.6.在conf.xml文件中注册userMapper.xml文件

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);
}
}

三、操作users表的CRUD

3.1.xml的实现

3.1.1.定义sql映射xml文件：

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


delete from users where id=#{id}


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


select * from users where id=#{id}


select * from users

3.1.2.在config.xml中注册这个映射文件

3.1.3.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

3.2.1.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 getAllUser();
}

3.2.2.在config中注册这个映射接口

3.2.3.在dao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;
}

四、几个可以优化的地方

4.1.连接数据库的配置可以单独放在一个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

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)

五、解决字段名与实体类属性名不相同的冲突

5.1.准备表和字段

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}

方式二: 通过

select * from orders where order_id=#{id}

六、实现关联表查询

6.1.一对一关联

6.1.1.提出需求

根据班级id查询班级信息(带老师的信息)

6.1.2.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);

6.1.3.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;
}

6.1.4.定义sql映射文件ClassMapper.xml

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 * from class where c_id=#{id}








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


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

6.1.5.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

6.2.1.提出需求

根据classId查询对应的班级信息,包括学生,老师

6.2.2.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);

6.2.3.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 students;
}

6.2.4.定义sql映射文件ClassMapper.xml

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 * from class where c_id=#{id}








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


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

6.2.5.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);
}

七、动态sql与模糊查询

7.1.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.准备数据库和表

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)

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

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 list = sqlSession.selectList(statement, new ConditionUser("%a%", 1, 12));
System.out.println(list);
}
}

MyBatis中可用的动态SQL标签

八、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

call mybatis.get_user_count(?,?)

8.5.测试

Map paramMap = new HashMap<>();
paramMap.put("sex_id", 0);
session.selectOne(statement, paramMap);
Integer userCount = paramMap.get("user_count");
System.out.println(userCount);

九、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

1.一级缓存: 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

9.2.1.根据任务查询

根据id查询对应的用户记录对象。

9.2.2.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);

9.2.3.创建表的实体类

public class User implements Serializable{
private int id;
private String name;
private int age;

9.2.4.userMapper.xml

select * from c_user where id=#{id}


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

9.2.5.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

9.3.1.添加一个在userMapper.xml中

9.3.2.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);
}

9.3.3.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

 //只读

十、Spring集成MyBatis

10.1.添加jar

【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 findAll();
}

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

insert into s_user(user_name,user_birthday,user_salary)
values(#{name},#{birthday},#{salary})


update s_user
set user_name = #{name},
user_birthday = #{birthday},
user_salary = #{salary}
where user_id = #{id}


delete from s_user
where user_id = #{id}


select *
from s_user
where user_id = #{id}


select *
from s_user

10.6.spring的配置文件: beans.xml

10.7.mybatis的配置文件: mybatis-config.xml

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 users = userMapper.findAll();
System.out.println(users);
}
}

以上所述是小编给大家介绍的MyBatis快速入门(简明浅析易懂)，希望对大家有所帮助，如果大家有任何疑问请给我留言，小编会及时回复大家的。在此也非常感谢大家对脚本之家网站的支持！