Mybatis持久层框架 | Lombok搭建

Lombok项目是一个java库，它可以自动插入到编辑器和构建工具中，增强java的性能。不需要再写getter、setter或equals方法，只要有一个注解，你的类就有一个功能齐全的构建器、自动记录变量……
使用步骤：
• IDEA中安装Lombok插件
• 项目中导入Lombok的jar包

    
        org.projectlombok
        lombok
        1.18.24
    

• 实体类中添加注解
import lombok.*;

@Data
@AllArgsConstructor
@NoArgsConstructor
public class User {
    private int id;
    private String name;
    private String password;

}
• @Data：无参构造、get/set方法、toString、hashCode、equals
• 服务器托管网@AllArgsConstructor：带参构造方法
• @NoArgsConstructor：无参构造方法
• @ToString：toString方法
• @EqualsAndHashCode：equals和hashCode方法
• @Getter：get方法
• @Setter：set方法

• 导入lombok

    
        org.projectlombok
        lombok
        1.18.24
    

• 新建实体类Teacher、Student
Teacher类
package com.wei.pojo;

import lombok.Data;

@Data
public class Teacher {
    private int id;
    private String name;
    //学生关联一个老师
    private Teacher teacher;
}
Student类
package com.wei.pojo;

import lombok.Data;

//多对一
@Data
public class Student {
    private int id;
    private String name;
    //学生需要关联一个老师
    private Teacher teacher;
}
• 建立Mapper接口
TeacherMapper接口
package com.wei.dao;

import com.wei.pojo.Teacher;
import org.apache.ibatis.annotations.Param;
import org.apache.ibatis.annotations.Select;

public interface TeacherMapper {

    @Select("select * from mybatis_03.teacher where id = #{tid}")
    Teacher getTeacher(@Param("tid") int id);
}
StudentMapper接口
package com.wei.dao;

public interface StudentMapper {

}
• 建立Mapper.xml文件
TeacherMapper.xml







StudentMapper.xml







• 核心配置文件mybatis-config.xml绑定注册接口


    
    

• 测试
public class MyTest {
    @Test
    public void test(){
        //取SqlSession对象
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        //获得TeacherMapper接口类
        TeacherMapper mapper = sqlSession.getMapper(TeacherMapper.class);

        Teacher teacher = mapper.getTeacher(1);
        System.out.println(teacher);

        //关闭SqlSession,避免造成内存出现问题
        sqlSession.close();
    }
}

环境搭建
• Student实体类
package com.wei.pojo;

import lombok.Data;

//多对一
@Data
public class Student {
    private int id;
    private String name;
    //学生需要关联一个老师
    private Teacher teacher;
}
• Teacher实体类
package com.wei.pojo;

import lombok.Data;

@Data
public class Teacher {
    private int id;
    private String name;
    //学生关联一个老师
    private Teacher teacher;
}

• Mapper.xml映射文件





    
    
        select * from mybatis_03.student;
    

    
        
        
        
        
    

    
        select * from mybatis_03.teacher where id=#{tid};
    

• Test测试类
@Test
    public void testStudent() {
        //取SqlSession对象
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        //获得StudentMapper接口类
        StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
        //获取getStudent学生信息
        List studentList = mapper.getStudent();

        for (Student student : studentList) {
            System.out.println(student);
        }

        //关闭SqlSession,避免造成内存出现问题
        sqlSession.close();
    }
}

• Mapper.xml映射文件


    select s.id sid, s.name sname,t.name tname from mybatis_03.student s , mybatis_03.teacher t where t.id=s.tid;



    
    
    
        
    

• Test测试类
@Test
public void testStudent2() {
    //取SqlSession对象
    SqlSession sqlSession = MybatisUtils.getSqlSession();
    //获得StudentMapper接口类
    StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
    //获取getStudent学生信息
    List studentList = mapper.getStudent2();

    for (Student student : studentList) {
        System.out.println(student);
    }

    //关闭SqlSession,避免造成内存出现问题
    sqlSession.close();
}

环境搭建
• Student实体类
package com.wei.pojo;

import lombok.Data;

//多对一
@Data
public cla服务器托管网ss Student {
    private int id;
    private String name;
    private int tid;
}
• Teacher实体类
package com.wei.pojo;

import lombok.Data;

import java.util.List;

@Data
public class Teacher {
    private int id;
    private String name;
    //一个老师拥有多个学生
    private List students;
}

• StudentMapper类
package com.wei.dao;

import com.wei.pojo.Student;

import java.util.List;

public interface StudentMapper {
    //查询所有的学生信息，以及对应的老师的信息
    public List getStudent2();
}
• TeacherMapper.xml映射文件

    select * from mybatis_03.teacher where id=#{tid};



    
    
    
    



    select * from mybatis_03.student where tid=#{tid};

• 测试
@Test
public void test2() {
    //获取sqlSession对象
    SqlSession sqlSession = MybatisUtils.getSqlSession();
    //获取TeacherMapper接口类
    TeacherMapper mapper = sqlSession.getMapper(TeacherMapper.class);

    Teacher teacher = mapper.getTeacher2(1);
    System.out.println(teacher);

    //关闭SqlSession,避免造成内存出现问题
    sqlSession.close();
}

• StudentMapper类
package com.wei.dao;

import com.wei.pojo.Student;

import java.util.List;

public interface StudentMapper {
    //查询所有的学生信息，以及对应的老师的信息
    public List getStudent();
}
• TeacherMapper.xml映射文件


    select s.id sid, s.name sname, t.name tname, t.id tid from mybatis_03.student s,mybatis_03.teacher t where t.id = s.tid and t.id=#{tid};




    
    
    
    
        
        
        
    

• 测试
public class MyTest {
    @Test
    public void test() {
        //获取sqlSession对象
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        //获取TeacherMapper接口类
        TeacherMapper mapper = sqlSession.getMapper(TeacherMapper.class);

        Teacher teacher = mapper.getTeacher(1);
        System.out.println(teacher);

        //关闭SqlSession,避免造成内存出现问题
        sqlSession.close();
    }
总结：
collection & association区别：
• 关联 - association [多对一]
• 集合 - collection [一对多]
javatype & oftype区别：
• javatype：指定实体类中属性的类型
• oftype：指定映射到List或者集合的pojo类型，泛型中的约束类型