MyBatis快速入门(简明浅析易懂)-eolink官网

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

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

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)

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

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)

"http://mybatis.org/dtd/mybatis-3-mapper.dtd">

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

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

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)

"http://mybatis.org/dtd/mybatis-3-mapper.dtd">

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

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

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

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

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

xsi:schemaLocation="

http://springframework.org/schema/beans

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

http://springframework.org/schema/context

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

http://springframework.org/schema/tx

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

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

10.7.mybatis的配置文件: mybatis-config.xml

PUBLIC "-//mybatis.org//DTD Config 3.0//EN"

"http://mybatis.org/dtd/mybatis-3-config.dtd">

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，会及时回复大家的。在此也非常感谢大家对我们网站的支持！

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

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)

"http://mybatis.org/dtd/mybatis-3-mapper.dtd">

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

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

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

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

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

xsi:schemaLocation="

http://springframework.org/schema/beans

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

http://springframework.org/schema/context

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

http://springframework.org/schema/tx

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

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

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

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

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

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

xsi:schemaLocation="

http://springframework.org/schema/beans

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

http://springframework.org/schema/context

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

http://springframework.org/schema/tx

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

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

10.7.mybatis的配置文件: mybatis-config.xml

PUBLIC "-//mybatis.org//DTD Config 3.0//EN"

"http://mybatis.org/dtd/mybatis-3-config.dtd">

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);

}

c#自定义Attribute获取接口实现示例代码

244 2023-06-30

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