[Java知识库]Mybatis学习——0221

什么是 MyBatis？?

MyBatis 是一个可以自定义 SQL、存储过程和高级映射的持久层框架。

maven中需要导入的依赖

<dependencies>
    <dependency>
      <groupId>mysql</groupId>
      <artifactId>mysql-connector-java</artifactId>
      <version>5.1.10</version>
    </dependency>
    <dependency>
      <groupId>org.mybatis</groupId>
      <artifactId>mybatis</artifactId>
      <version>3.4.6</version>
    </dependency>
    <dependency>
      <groupId>org.projectlombok</groupId>
      <artifactId>lombok</artifactId>
      <version>1.18.12</version>
      <scope>provided</scope>
    </dependency>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.11</version>
      <scope>test</scope>
    </dependency>
  </dependencies>

新建一个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>
        <package name="bean"/>
    </typeAliases>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <!-- 从配置文件中加载属性 -->
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/r0221"/>
                <property name="username" value="sa"/>
                <property name="password" value="1"/>
            </dataSource>
        </environment>
    </environments>

    <mappers>
        <!-- 加载前面编写的SQL语句的文件 -->
        <mapper resource="mapper/StudentMapper.xml"/>
    </mappers>

</configuration>

结构大概为这样

mapper下的xml是为了编写sql语句头文件为

?

<?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">

util的

package util;

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 java.io.IOException;
import java.io.InputStream;

public class MybatisUtil {
    private static SqlSessionFactory sqlSessionFactory;
    static {
        try {
            String r="mybatis-config.xml";
            InputStream is= Resources.getResourceAsStream(r);
            sqlSessionFactory=new SqlSessionFactoryBuilder().build(is);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static SqlSession getSqlSession() {
        return sqlSessionFactory.openSession();
    }

    public static void closesession(SqlSession session){
        if(session!=null){
            session.close();;
        }
    }
}

用maven写的可能运行会出现这个错误org.apache.ibatis.builder.BuilderException:?Error?parsing?SQL?Mapper?Configuration.?Cause:?java.io.IOException:?Could?not?find?resource?mapper/StudentMapper.xml

是因为maven里面约定大于配置，导致资源导出失败

解决方法在pom.xml的build里面加个

<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>