Mybatis学习笔记

Mybatis代码

Mybatis入门

https://mybatis.net.cn/getting-started.html

写一个Mybatis项目

1、新建一个Maven项目

2、导入依赖集

    <!--  导入依赖  -->
    <dependencies>
        <!--mysql驱动-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.47</version>
        </dependency>
        <!--mybatis-->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.2</version>
        </dependency>
        <!--junit-->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
        </dependency>
    </dependencies>

3、创建模块，配置mybatis核心文件mybatis-config.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核心配置文件-->
<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?characterEncoding=UTF-8"/>
                <property name="username" value="root"/>
                <property name="password" value="root"/>
            </dataSource>
        </environment>
    </environments>

    <!--  每一个Mapper.xml都需要在mybatis核心配置文件中注册！  -->
    <mappers>
        <mapper resource="com/github/subei/dao/UserMapper.xml"/>
    </mappers>

</configuration>

连接了数据库，创建对象类（pojo）

创建Dao层（业务逻辑操作）接口

创建一个userDao

package com.github.dao;

import com.github.pojo.User;

import java.util.List;

public interface UserDao {
    List<User> getUserList();
}

接下来继承这个接口

<?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">
<!-- namespace=绑定一个对应的Dao/Mapper接口 -->
<mapper namespace="com.github.subei.dao.UserDao">

    <!--select查询语句-->
    <select id="getUserList" resultType="com.github.subei.pojo.User">
        select * from mybatis.user;
    </select>

</mapper>

报错问题

1、Error creating document instance. Cause: com.sun.org.apache.xerces.internal.impl.io.MalformedByteSequenceException: 1 字节的 UTF-8 序列的字节 1 无效。

解决方法：在settings中找到file encoding 将字符集设置为utf-8

2、java.lang.ExceptionInInitializerError at com.kuang.dao.UserDaoTest.test(UserDaoTest.java:15)

在所有xml代码中添加一下代码

<!--在build中配置resources，来防止我们资源导出失败的问题-->
    <build>
        <resources>
            <resource>
                <directory>src/main/resources</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>true</filtering>
            </resource>
            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>true</filtering>
            </resource>
        </resources>
    </build>

注意事项：

1、在mybatis-config.xml中，需要对创建的xml（这里的xml文件不在resource中）注册