【框架学习】Mybatis简解

mybatis 作为目前十分流行的持久层框架，比起hibernate有很大优势
hibernate特点：hql，虽然说屏蔽了数据库差异，但是过于笨重，不方便进行sql优化，，特点比较”鸡肋“
mybatis特点：轻便，对持久层进行轻量的封装，可直接使用sql语句进行查询，提供动态sql，强大的 resultMap。

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一。一个简单的案例

mybatis-cfg.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>


    <properties resource="jdbc.properties"></properties>
    <environments default="mybatis-demo">
        <environment id="mybatis-demo">
            <transactionManager type="JDBC"></transactionManager>
            <dataSource type="POOLED">
                <property name="driver" value="${jdbc.driver}"></property>
                <property name="url" value="${jdbc.url}"></property>
                <property name="username" value="${jdbc.username}"></property>
                <property name="password" value="${jdbc.password}"></property>
            </dataSource>
        </environment>
    </environments>

    <mappers>
        <mapper resource="TeacherMapper.xml"></mapper>
        <mapper class="xatu.zsl.dao.student.TestMapper"></mapper>
    </mappers>

</configuration>

studentMapper.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="xatu.zsl.dao.student.StudentMapper">

    <resultMap id="studentMapper" type="xatu.zsl.entity.Student">
        <id column="id" property="id"></id>
        <result property="name" column="name"></result>
    </resultMap>

    <select id="selectAllStudent"  resultMap="studentMapper">
        SELECT id,name FROM student
    </select>
</mapper>

MainTest.java

package xatu.zsl.main;

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 xatu.zsl.entity.Student;

import java.io.*;
import java.util.List;

/**
 * Created by zsl on 2017/8/2.
 */
public class MainTest {

    public static void main(String[] args) throws Exception {
        InputStream is = Resources.getResourceAsStream("mybatis-cfg.xml");
        SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(is);
        SqlSession session = sessionFactory.openSession();
        List<Student> students = session.selectList("xatu.zsl.dao.student.StudentMapper.selectAllStudent");
        for (Student student : students
                ) {
            System.out.println(student.getName() + "      " + student.getId());
        }
        session.close();
    }
}

（1）.读取配置文件（一个就好适合单例）

Resources.getResourceAsStream("mybatis-cfg.xml");

当然也可以读取成其他格式，getResourceAsStream，，这个方法提供多种读取方式


（2）构建SqlSessionFactory（一个就好，适合单例）
通过建造者模式，构建出SqlSessionFactory，，，建造者模式解释

SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(is);

当然 build提供多种构建方式。。。。

（3）获取SqlSession（线程私有，需要关闭）
SqlSession，是与数据库的一次回话，需要关闭，session.close();，，
所以是以打开形式创建的。

SqlSession session = sessionFactory.openSession();

（4）使用SqlSession，操作数据库
SqlSession提供众多方法供使用。

session.selectList("xatu.zsl.dao.student.StudentMapper.selectAllStudent");

---

二。使用注解方式更方便

import org.apache.ibatis.annotations.Insert;
import org.apache.ibatis.annotations.Param;
import xatu.zsl.entity.Student;

/**
 * Created by zsl on 2017/8/4.
 */

public interface TestMapper {

    @Insert("INSERT INTO student(id,name) VALUES (#{id},#{name})")
    public int insertStudent(Student student);
}

 public static void main(String[] args) throws IOException {
        InputStream is = Resources.getResourceAsStream("mybatis-cfg.xml");
        SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(is);
        SqlSession session = sessionFactory.openSession(true);
//        创建学生
        Student xiaoming = new Student();
        xiaoming.setId(22);
        xiaoming.setName("小明");
        //获取mapper
        TestMapper mapper = session.getMapper(TestMapper.class);
        mapper.insertStudent(xiaoming);
        session.close();
    }

注意：此处木有session.commit()居然提交成功了，，，，
原因是：sessionFactory.openSession(true);
不加true，需要commit（）

---

三。注意事项

所有的 mapper，，不管是xml，还是java的，，都需要在mybatis-cfg.xml中进行配置


下面分别是配置，文件和class

    <mappers>
        <mapper resource="TeacherMapper.xml"></mapper>
        <mapper class="xatu.zsl.dao.student.TestMapper"></mapper>
    </mappers>

否则会出现错误：

Exception in thread "main" org.apache.ibatis.binding.BindingException: Type interface xatu.zsl.dao.student.TestMapper is not known to the MapperRegistry.
    at org.apache.ibatis.binding.MapperRegistry.getMapper(MapperRegistry.java:47)
    at org.apache.ibatis.session.Configuration.getMapper(Configuration.java:675)
    at org.apache.ibatis.session.defaults.DefaultSqlSession.getMapper(DefaultSqlSession.java:250)
    at xatu.zsl.main.MainTest.main(MainTest.java:40)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:483)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:147)