mybatis学习

2022-04-18 15:21:52

什么是 MyBatis ？

MyBatis 是支持定制化 SQL、存储过程以及高级映射的优秀的持久层框架。MyBatis 避免了几乎所有的 JDBC 代码和手动设置参数以及获取结果集。MyBatis 可以对配置和原生Map使用简单的 XML 或注解，将接口和 Java 的 POJOs(Plain Old Java Objects,普通的 Java对象)映射成数据库中的记录。

教程链接

https://mybatis.github.io/mybatis-3/zh/index.html

第一个helloworld程序源代码

①导入jar包

mybatis-3.2.8.jar

mysql-connector-java-5.1.18-bin.jar

②配置mybatis的配置文件Configuration.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>
<typeAliases>
<typeAlias alias="User" type="com.oracle.pojo.User"/>
</typeAliases>

<!--environments 可以填两种值

development：开发者模式

work：工作模式

-->

<mappers>
<mapper resource="com/oracle/pojo/User.xml"/>
</mappers>
</configuration>

③实体类

package com.oracle.pojo;

public class User {

private int id;
private String userName;
private String userAge;
private String userAddress;

public int getId() {
return id;
}

public void setId(int id) {
this.id = id;
}

public String getUserName() {
return userName;
}

public void setUserName(String userName) {
this.userName = userName;
}

public String getUserAge() {
return userAge;
}

public void setUserAge(String userAge) {
this.userAge = userAge;
}

public String getUserAddress() {
return userAddress;
}

public void setUserAddress(String userAddress) {
this.userAddress = userAddress;
}

@Override
public String toString() {
return "User [id=" + id + ", userName=" + userName + ", userAge="
+ userAge + ", userAddress=" + userAddress + "]";
}

}

④实体类的配置文件User.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.oracle.pojo.UserMapper">
<select id="selectUserByID" parameterType="int" resultType="User">
select * from user where id = #{id}
</select>
</mapper>

⑤测试类

package com.oracle.test;

import java.io.Reader;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

import com.oracle.pojo.User;

public class Test {
private static SqlSessionFactory sqlSessionFactory;
private static Reader reader;

static{
try{
reader = Resources.getResourceAsReader("Configuration.xml");
sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
}catch(Exception e){
e.printStackTrace();
}
}

public static SqlSessionFactory getSession(){
return sqlSessionFactory;
}

public static void main(String[] args) {
SqlSession session = sqlSessionFactory.openSession();
try {

//"com.oracle.pojo.UserMapper.selectUserByID"是根据实体类的配置文件写的，com.oracle.pojo.UserMapper是配置文件的namespace，selectUserByID是select的id
User user = (User) session.selectOne("com.oracle.pojo.UserMapper.selectUserByID", 1);
System.out.println(user);
} finally {
session.close();
}
}
}

基于xml实现crud

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="net/lamp/java/ibatis/bean/userMapper.xml"/>

3). 在dao 中调用：

/*//增
int count = session.insert("com.oracle.pojo.UserMapper.addUser", new User(-1,"kkk","12","nnnn"));
System.out.println(count);*/

/*改
* int count = session.update("com.oracle.pojo.UserMapper.updateUser", new User(3, "kkk2222", "30", "mmmmmm"));
System.out.println(count);*/

/*删
* session.delete("com.oracle.pojo.UserMapper.deleteUser", 3);*/

/*获取所有
* List<User> users = session.selectList("com.oracle.pojo.UserMapper.getAllUser");
System.out.println(users);*/

/*获取一个
* User user = (User) session.selectOne("com.oracle.pojo.UserMapper.selectUserByID", 1);
System.out.println(user);*/

基于注解实现crud

1). 定义sql 映射的接口

package com.oracle.pojo;

import java.util.List;

import org.apache.ibatis.annotations.Delete;
import org.apache.ibatis.annotations.Insert;
import org.apache.ibatis.annotations.Select;
import org.apache.ibatis.annotations.Update;

public interface UserMapperImp {
@Insert("insert into user(userName,userAge,userAddress) values (#{userName},#{userAge},#{userAddress})")
public int add(User user);
@Delete("delete from user where id = #{id}")
public void delete(int id);
@Update("update user set userName=#{userName},userAge=#{userAge},userAddress=#{userAddress} where id=#{id}")
public void update(User user);
@Select("select * from user")
public List<User> getAll();
@Select("select * from user where id = #{id}")
public User getOne(int id);
}

2). 在config 中注册这个映射接口

3). 在dao 类中调用

//--------基于注解---------
UserMapperImp mapper = session.getMapper(UserMapperImp.class);
//mapper.add(new User(-1, "bb", "22", "cc"));
//mapper.delete(4);
//mapper.update(new User(5, "bbbb", "22", "cc"));
/*List<User> users = mapper.getAll();
System.out.println(users);*/
User user = mapper.getOne(1);
System.out.println(user);

几个可以优化的地方

连接数据库的配置单独放在一个properties 文件中

在配置文件中

为实体类定义别名,简化sql 映射xml 文件中的引用

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.配置log4j.xml
<?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>

码农公寓

什么是 MyBatis ？

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