MyBatis快速入门(简明浅析易懂)_Java教程-查字典教程网

摘要：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...

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

<"1.0" encoding="UTF-8"?> <!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd"> <configuration> <environments default="development"> <environment id="development"> <transactionManager type="JDBC" /> <dataSource type="POOLED"> <property name="driver" value="com.mysql.jdbc.Driver" /> <property name="url" value="jdbc:mysql://localhost:3306/mybatis" /> <property name="username" value="root" /> <property name="password" value="root" /> </dataSource> </environment> </environments> </configuration>

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

<"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.atguigu.mybatis_test.test1.userMapper"> <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

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 id="insertUser" parameterType="com.atguigu.ibatis.bean.User"> insert into users(name, age) values(#{name}, #{age}); </insert> <delete id="deleteUser" parameterType="int"> delete from users where id=#{id} </delete> <update id="updateUser" parameterType="com.atguigu.ibatis.bean.User"> update users set name=#{name},age=#{age} where id=#{id} </update> <select id="selectUser" parameterType="int" resultType="com.atguigu.ibatis.bean.User"> select * from users where id=#{id} </select> <select id="selectAllUsers" resultType="com.atguigu.ibatis.bean.User"> select * from users </select>

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<User> 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<br> <properties resource="db.properties"/> <property name="driver" value="${driver}" /> <property name="url" value="${url}" /> <property name="username" value="${username}" /> <property name="password" value="${password}" />

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)

<"1.0" encoding="UTF-8" ?> <!DOCTYPE log4j:configuration SYSTEM "log4j.dtd"> <log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/"> <appender name="STDOUT"> <layout> <param name="ConversionPattern" value="%-5p %d{MM-dd HH:mm:ss,SSS} %m (%F:%L) n" /> </layout> </appender> <logger name="java.sql"> <level value="debug" /> </logger> <logger name="org.apache.ibatis"> <level value="debug" /> </logger> <root> <level value="debug" /> <appender-ref ref="STDOUT" /> </root> </log4j:configuration>

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 id="selectOrder" parameterType="int" resultType="_Order"> select order_id id, order_no orderNo,order_price price from orders where order_id=#{id} </select>

方式二: 通过<resultMap>

<select id="selectOrderResultMap" parameterType="int" resultMap="orderResultMap"> select * from orders where order_id=#{id} </select> <resultMap type="_Order" id="orderResultMap"> <id property="id" column="order_id"/> <result property="orderNo" column="order_no"/> <result property="price" column="order_price"/> </resultMap>

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 id="getClass3" parameterType="int" resultMap="ClassResultMap3"> 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> <resultMap type="_Classes" id="ClassResultMap3"> <id property="id" column="c_id"/> <result property="name" column="c_name"/> <association property="teacher" column="teacher_id" javaType="_Teacher"> <id property="id" column="t_id"/> <result property="name" column="t_name"/> </association> <> <collection property="students" ofType="_Student"> <id property="id" column="s_id"/> <result property="name" column="s_name"/> </collection> </resultMap>  <select id="getClass4" parameterType="int" resultMap="ClassResultMap4"> select * from class where c_id=#{id} </select> <resultMap type="_Classes" id="ClassResultMap4"> <id property="id" column="c_id"/> <result property="name" column="c_name"/> <association property="teacher" column="teacher_id" javaType="_Teacher" select="getTeacher2"></association> <collection property="students" ofType="_Student" column="c_id" select="getStudent"></collection> </resultMap> <select id="getTeacher2" parameterType="int" resultType="_Teacher"> SELECT t_id id, t_name name FROM teacher WHERE t_id=#{id} </select> <select id="getStudent" parameterType="int" resultType="_Student"> SELECT s_id id, s_name name FROM student WHERE class_id=#{id} </select>

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<Student> students; }

6.2.4.定义sql映射文件ClassMapper.xml

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)

<"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.atguigu.day03_mybatis.test6.userMapper"> <select id="getUser" parameterType="com.atguigu.day03_mybatis.test6.ConditionUser" resultType="com.atguigu.day03_mybatis.test6.User"> select * from d_user where age>=#{minAge} and age<=#{maxAge} <if test='name!="%null%"'>and name like #{name}</if> </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

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

<mapper namespace="com.atguigu.mybatis.test7.userMapper">  <select id="getCount" statementType="CALLABLE" parameterMap="getCountMap"> call mybatis.get_user_count(?,?) </select> <parameterMap type="java.util.Map" id="getCountMap"> <parameter property="sex_id" mode="IN" jdbcType="INTEGER"/> <parameter property="user_count" mode="OUT" jdbcType="INTEGER"/> </parameterMap> </mapper>

8.5.测试

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);

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

<"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.atguigu.mybatis.test8.userMapper"> <select id="getUser" parameterType="int" resultType="_CUser"> select * from c_user where id=#{id} </select> <update id="updateUser" parameterType="_CUser"> update c_user set name=#{name}, age=#{age} where id=#{id} </update> </mapper>

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<cache>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

<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

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<User> findAll(); }

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

<"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.atguigu.mybatis.test9.UserMapper"> <resultMap type="User" id="userResult"> <result column="user_id" property="id"/> <result column="user_name" property="name"/> <result column="user_birthday" property="birthday"/> <result column="user_salary" property="salary"/> </resultMap> <> <insert id="save" keyColumn="user_id" keyProperty="id" useGeneratedKeys="true"> insert into s_user(user_name,user_birthday,user_salary) values(#{name},#{birthday},#{salary}) </insert> <update id="update"> update s_user set user_name = #{name}, user_birthday = #{birthday}, user_salary = #{salary} where user_id = #{id} </update> <delete id="delete"> delete from s_user where user_id = #{id} </delete> <select id="findById" resultMap="userResult"> select * from s_user where user_id = #{id} </select> <select id="findAll" resultMap="userResult"> select * from s_user </select> </mapper>

10.6.spring的配置文件: beans.xml

<"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" > <property name="driverClassName" value="com.mysql.jdbc.Driver"/> <property name="url" value="jdbc:mysql://localhost:3306/mybatis"/> <property name="username" value="root"/> <property name="password" value="root"/> </bean>  <bean id="sqlSessionFactory"> <property name="dataSource" ref="dataSource"/> <property name="typeAliasesPackage" value="com.atuigu.spring_mybatis2.domain"/> </bean>  <bean> <property name="basePackage" value="com.atuigu.spring_mybatis2.mapper"/> <property name="sqlSessionFactory" ref="sqlSessionFactory"/> </bean> <> <bean id="txManager"> <property name="dataSource" ref="dataSource"/> </bean> <> <tx:annotation-driven transaction-manager="txManager" /> </beans>

10.7.mybatis的配置文件: mybatis-config.xml

<"1.0" encoding="UTF-8" ?> <!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd"> <configuration> <> <> <> <> <> </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); } }

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们留言，小编会及时回复大家的。在此也非常感谢大家对查字典教程网的支持！