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.
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】 |
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"> <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">
<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
<mappers> <mapper resource="com/atguigu/mybatis_test/test1/userMapper.xml"/> </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 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>
2). 在config.xml中注册这个映射文件
<mapper resource=" com/atguigu/ibatis/bean/userMapper.xml"/>
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
<mapper class="com.atguigu.ibatis.crud.ano.UserMapper"/>
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
<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
<typeAliases> <typeAlias type="com.atguigu.ibatis.bean.User" alias="_User"/> </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/"> <appender name="STDOUT" class="org.apache.log4j.ConsoleAppender"> <layout class="org.apache.log4j.PatternLayout"> <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> |
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 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>
<resultMaptype="_Order" id="orderResultMap"> <id property="id" column="order_id"/> <result property="orderNo" column="order_no"/> <result property="price" column="order_price"/> </resultMap> |