Mybatis—学习基础

版权声明： https://blog.csdn.net/qq_34866380/article/details/80155322

Mybatis基于java的持久层框架，内部封装了JDBC，使开发只需要关注SQL语句。Mybatis通过xml或注解方式将要执行的各种statement配置，通过java对象和Statement中SQL的动态参数进行映射生成最终执行的SQL语句，最后由Mybatis框架执行SQL并将结果映射成Java对象并返回。

Mybatis工作原理图：

---

简单实现Mybatis

1、实体类
Student.java

public class Student {

    private Integer id;
    private String name;
    private int age;
    private double score;
    public Student() {
        super();

    }
    public Student( String name, int age, double score) {
        super();

        this.name = name;
        this.age = age;
        this.score = score;
    }
    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public double getScore() {
        return score;
    }
    public void setScore(double score) {
        this.score = score;
    }
    @Override
    public String toString() {
        return "Student [id=" + id + ", name=" + name + ", age=" + age + ", score=" + score + "]";
    }



}

2、sql文件

SET FOREIGN_KEY_CHECKS=0;

-- ----------------------------
-- Table structure for student
-- ----------------------------
DROP TABLE IF EXISTS `student`;
CREATE TABLE `student` (
  `id` int(5) NOT NULL AUTO_INCREMENT,
  `name` varchar(20) DEFAULT NULL,
  `age` int(3) DEFAULT NULL,
  `score` double DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=latin1;

-- ----------------------------
-- Records of student
-- ----------------------------
INSERT INTO `student` VALUES ('1', 'lov1', '20', '99.9');
INSERT INTO `student` VALUES ('2', 'lov2', '22', '69.5');
INSERT INTO `student` VALUES ('3', 'lov3', '21', '66');

-- ----------------------------
-- Table structure for user
-- ----------------------------
DROP TABLE IF EXISTS `user`;
CREATE TABLE `user` (
  `userid` varchar(30) NOT NULL,
  `name` varchar(30) NOT NULL,
  `password` varchar(32) NOT NULL,
  PRIMARY KEY (`userid`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

-- ----------------------------
-- Records of user
-- ----------------------------
INSERT INTO `user` VALUES ('admin', 'admin', 'admin');

3、配置文件
mybatis.xml（根目录下，规定命名；连接数据库，加载其他相关配置文件）

<?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>
    <!-- 注册db连接属性文件 -->
    <properties resource="jdbc_mysql.properties" />
    <!-- 定义类型别名 -->
    <typeAliases>
       <!-- <typeAlias type="com.lov.beans.Student" alias="Student"/> -->
       <!-- 将指定包中的所有类的简单类名当作其别名 -->
       <package name="com.lov.beans"/>
    </typeAliases>
    <!-- 配置运行环境 -->
    <environments default="mysqlEM">
         <environment id="mysqlEM">
              <transactionManager type="JDBC"></transactionManager>
              <dataSource type="POOLED">
                  <property name="driver" value="${jdbc.driver}"/>
                  <!-- jdbc:mysql:///lov 默认的127.0.0.1可以省略-->
                  <property name="url" value="${jdbc.url}"/>
                  <property name="username" value="${jdbc.username}"/>
                  <property name="password" value="${jdbc.password}"/>
              </dataSource>
         </environment>

    </environments>
    <!-- 注册映射文件mapper.xml -->
    <mappers>
      <mapper resource="com/lov/dao/mapper.xml"/>
    </mappers>

</configuration>

mapper.xml（相应的bean目录文件下，需在mybatis.xml文件中注册）

<?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.lov.dao.IStudentDao">
           <!--namespace作用：在有多个mapper.xml文件，且文件中有相同sql语句，可通过namespace区别，namespace不可重复-->
   <!-- 这里写的是sql语句，这里用简单实现insert-->
   <insert id="insertStudent" parameterType="Student">
        <!-- id:在dao实现类中引用的sql语句名字；paramterType：可通过在mybatis.xml中定义的实体类别名，或相应类的全限定性类名-->
        insert into student(name,age,score) value (#{name},#{age},#{score})
    </insert>

</mapper>

mysql.properties（连接四要素，需在mybatis.xml注册）

jdbc.driver=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://127.0.0.1:3306/lov
jdbc.username=root
jdbc.password=password

log4j.properties（用log4j输出日志）

### 输出信息到控制抬 ###
log4j.appender.console = org.apache.log4j.ConsoleAppender

log4j.appender.console.Target=System.out

log4j.appender.console.layout=org.apache.log4j.PatternLayout

log4j.appender.console.layout.ConversionPattern= %m%n

 ### 设置###
log4j.logger.com.lov.dao.IStudentDao = debug,console

4、dao实现类
IStudentDao.java

import java.util.List;
import java.util.Map;

import com.lov.beans.Student;

public interface IStudentDao {

    void insertStudent(Student student);
    void insertStudentCacheId(Student student);

    void deleteStudentById(int id);
    void updateStudent(Student student);

    List<Student> selectAllStudents();
    Map<String,Object> selectAllStudentsMap();

    Student selectStudentById(int id);
    List<Student> selectStudentsByName(String name);
}

StudentDaoImpl.java

import org.apache.ibatis.session.SqlSession;


import com.lov.beans.Student;
import com.lov.utils.MyBatisUtils;

public class StudentDaoImpl implements IStudentDao {

    private SqlSession sqlSession;

    @Override
    public void insertStudent(Student student) {

        try {
            //变成工具类中执行
            /*InputStream inputStream;
            //1、加载主配置文件
            inputStream = Resources.getResourceAsStream("mybatis.xml");
            //2、创建SqlSessionFactory对象
            SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream );
            //3、创建SqlSession对象
            sqlSession = sqlSessionFactory.openSession();*/
            sqlSession = MyBatisUtils.getSqlSession();
            //4、相关操作
            sqlSession.insert("insertStudent", student);//mapper.xml的sqlid

            sqlSession.commit();//提交后自动进行事务回滚
        }finally {
            if(sqlSession != null){
                sqlSession.close();//sqlSession实质是流的操作
            }
        }



    }

    @Override
    public void insertStudentCacheId(Student student) {


    }

    @Override
    public void deleteStudentById(int id) {

    }

    @Override
    public void updateStudent(Student student) {

    }

    @Override
    public List<Student> selectAllStudents() {
          return null;
    }

    @Override
    public Map<String, Object> selectAllStudentsMap() {
          return null;
    }

    @Override
    public Student selectStudentById(int id) {
          return null;
    }

    @Override
    public List<Student> selectStudentsByName(String name) {

          return null;
    }

}

5、工具类
MybatisUtils.java

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


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

public class MyBatisUtils {

    private static SqlSessionFactory sqlSessionFactory;

    public  static SqlSession getSqlSession(){
        InputStream is;
        try {
            is = Resources.getResourceAsStream("mybatis.xml");

            if(sqlSessionFactory == null){
                sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);
            }
            return sqlSessionFactory.openSession();
        } catch (IOException e) {

            e.printStackTrace();
        }
        return null;
    }
}

6、测试类
Mytest.java（Junit做测试）

import org.junit.After;
import org.junit.Before;
import org.junit.Test;

import com.lov.beans.Student;
import com.lov.dao.IStudentDao;
import com.lov.dao.StudentDaoImpl;


public class MyTest {

    private IStudentDao dao;

    @Before
    public void before(){
        dao = new StudentDaoImpl();
    }

    @Test
    public void testInsert(){

        Student student = new Student("lov_1",22,98.5);
        dao.insertStudent(student);

    }

}