【Mybatis学习笔记3】配置文件别名的3种方法

正常情况下，我们UserMapper.xml每个select接口的resultType都会写具体的实体类名，但如下图样式会很冗余。

<?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.coke.dao.UserMapper">

    <select id="getUserList"  resultType="com.coke.pojo.User">
        select * from mybatis.user
    </select>

</mapper>

 

我们可以通过以下几种方法，简化操作！

 

方法一、mybatis-config.xml中添加别名。

这种方法适用于实体类较少的时候，一一对应。

<?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>

    <!--别名-->
    <typeAliases>
        <typeAlias type="com.coke.pojo.User" alias="User"/>
    </typeAliases>

    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC" />
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.cj.jdbc.Driver" />
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis?useUnicode=true&amp;serverTimezone=Asia/Shanghai&amp;allowMultiQueries=TRUE" />
                <property name="username" value="root" />
                <property name="password" value="123456" />
            </dataSource>
        </environment>
    </environments>

    <mappers>
        <mapper resource="com/coke/dao/UserMapper.xml" />
    </mappers>
</configuration>

然后UserMapper.xml里可以修改为：

<?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.coke.dao.UserMapper">

    <select id="getUserList"  resultType="User">
        select * from mybatis.user
    </select>

</mapper>

 

方法二、mybatis-config.xml中添加别名（扫描包）

<?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>
        <package name="com.coke.pojo"/>
    </typeAliases>

    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC" />
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.cj.jdbc.Driver" />
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis?useUnicode=true&amp;serverTimezone=Asia/Shanghai&amp;allowMultiQueries=TRUE" />
                <property name="username" value="root" />
                <property name="password" value="123456" />
            </dataSource>
        </environment>
    </environments>

    <mappers>
        <mapper resource="com/coke/dao/UserMapper.xml" />
    </mappers>
</configuration>

mybatis会自动扫描该包下的实体类，UserMapper.xml里的resultType以方法名的小写命名即可（大写也行）

<?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.coke.dao.UserMapper">

    <select id="getUserList"  resultType="User">
        select * from mybatis.user
    </select>

</mapper>

 

方法三、实体类上加注解

package com.coke.pojo;

// 实体类

import org.apache.ibatis.type.Alias;

@Alias(value = "mybatis")
public class User {

    private int id;
    private String name;
    private String pwd;

    public User() {
    }

    public User(int id, String name, String pwd) {
        this.id = id;
        this.name = name;
        this.pwd = pwd;
    }

    public int getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getPwd() {
        return pwd;
    }

    public void setPwd(String pwd) {
        this.pwd = pwd;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", pwd='" + pwd + '\'' +
                '}';
    }
}

<?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.coke.dao.UserMapper">

    <select id="getUserList"  resultType="mybatis">
        select * from mybatis.user
    </select>

</mapper>