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的学习是程序员的必修课。今天小编通过分享本教程帮助大家快速入门mybatis，对mybatis入门知识感兴趣的朋友参考下吧
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
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);
2.4.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
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
3.1.3.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(); }
3.2.3.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
4.3.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)
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; }
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
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); }
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 ageand 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); } }
八、调用存储过程
8.1.提出需求
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
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
9.3.2.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编程之家网站的支持！
