Mybatis使用及原理解析
MyBatis 是一个基于Java的持久层框架。它提供的持久层框架包括SQL Maps和Data Access Objects（DAO）。
MyBatis 是支持普通 SQL查询，存储过程和高级映射的优秀持久层框架。MyBatis 消除了几乎所有的JDBC代码和参数的手工设置以及结果集的检索。MyBatis 使用简单的 XML或注解用于配置和原始映射，将接口和 Java 的POJO（Plain Old Java Objects，普通的 Java对象）映射成数据库中的记录
每个MyBatis应用程序主要都是使用SqlSessionFactory实例的，一个SqlSessionFactory实例可以通过SqlSessionFactoryBuilder获得。SqlSessionFactoryBuilder从一个xml配置文件或者一个预定义的配置类的实例获得配置信息。
使用：
1准备资源
1.1数据库中建立相应的表
CREATE DATABASE mybatis;
USE mybatis;
CREATE TABLE tb_user(
id INT PRIMARY KEY AUTO_INCREMENT,
NAME VARCHAR(16),
age INT
);
INSERT INTO tb_user(NAME, age) VALUES('phf1', 12);
INSERT INTO tb_user(NAME, age) VALUES('phf2', 20);
INSERT INTO tb_user(NAME, age) VALUES('phf3', 30);1.2 jar包
2.在eclipse中测试使用
2.1导入jar包。
2..2建一个mybatis-config.xml配置文件
可以在工程的src目录下
2.3 为封装SqlSessionFactory建个单例
package org.phf.factory;
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 MybatisFactory {
/**
* SqlSessionFactory对象可以看成DataSource（数据库连接池）
* 在应用执行期间，应该只创建一次，建议使用单例模式
* 通过SqlSessionFactoryBuilder来获得数据库配置参数并创建
*/
private static SqlSessionFactory sqlSessionFactory;
/**
* SqlSession对象可以理解成对Connection的封装，即一个数据连接会话
* 它同时也封装了连接和断开过程，提供sql语句的映射
* SqlSession实例不能被共享，它不是线程安全的。
* 所以应该一次性用完后要确保使用finally块来关闭它，关闭时会被收回SqlSessionFactory所管理的连接池中
*/
//private static SqlSession session;
static
{
try {
String resource = "mybatis-config.xml";
InputStream is = Resources.getResourceAsStream(resource);
sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);
System.out.println(sqlSessionFactory);
} catch (Exception e) {
e.printStackTrace();
}
}
//
public static SqlSession getSqlSession()
{
return sqlSessionFactory.openSession();
}
//
public static void close(SqlSession session)
{
if(session != null)
session.close();
}
}
2.4为每个表建一个映射类
package org.phf.pojo;
/**
* 数据库表的映射类，每个实例对象映射到表中的一行数据
* 属性的名称和类型对应表中字段名和类型，并提供getter和setter方法
* @author Administrator
*/
public class User {
private Integer id;
private String name;
private Integer age;
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 Integer getAge() {
return age;
}
public void setAge(Integer age) {
this.age = age;
}
@Override
public String toString() {
return "User [id=" + id + ", name=" + name + ", age=" + age + "]\n";
}
}
2.5建XXXmapper.xml文件和XXXmapper.java接口文件
创建每个表映射类创建的XXXmapper.xml配置文件，并创建相应XXXmapper接口(即数据存取接口),mapper配置文件和接口文件放在同一包目录下
//UserMapper.java
package org.phf.mapping;
import java.util.List;
import java.util.Map;
import org.phf.pojo.User;
/**
* 只要定义接口方法，所需sql语句在相应UserMapper.xml中映射
*/
public interface UserMapper {
//一条数据可以返回表对象，属性对应列名
User find(Integer id);
//一条数据还可以返回Map，key对应列名
Map findMap(Integer id);
//多条数据返回List集合
List findAll();
//最多接受一个参数，所以多个参数可以封装成对象传参,
List findWithIf(User user);
//多个键值对参数也可以用map传参，key对应列名，value对应列值
List findByNameAndAge(Map map);
//多个单值参数也可以用List传参,条件中使用IN操作符
List findWithIn(List ids);
//条件中使用like操作符
List findWithLike(String name);
} 2.6测试代码
package org.phf.test;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.junit.Test;
import org.phf.factory.MybatisFactory;
import org.phf.mapping.UserMapper;
import org.phf.pojo.User;
public class TestUserMapper {
@Test
public void test()
{
SqlSession session = null;
try {
//获取SqlSession的对象(需要手动关闭该资源)
session = MybatisFactory.getSqlSession();
//获取业务接口，通过接口类型获取由mybatis生成的匿名实例
UserMapper userMapper = session.getMapper(UserMapper.class);
//调用接口方法，执行操作且获得数据
System.out.println("<---------find by id----------->");
User user = userMapper.find(1);
System.out.println(user);
System.out.println("<---------findMap----------->");
Map map = userMapper.findMap(2);
System.out.println(map);
System.out.println("<---------findAll----------->");
List userList = userMapper.findAll();
System.out.println(userList);
System.out.println("<---------findWithIf----------->");
user = new User();
user.setName("phf");
userList = userMapper.findWithIf(user);
System.out.println(userList);
System.out.println("<---------findByNameAndAge----------->");
Map map1 = new HashMap();
map1.put("age", 10);
userList = userMapper.findByNameAndAge(map1);
System.out.println(userList);
System.out.println("<---------findWithIn----------->");
List list = new ArrayList<>();
list.add(1);
list.add(5);
list.add(10);
userList = userMapper.findWithIn(list);
System.out.println(userList);
System.out.println("<---------findWithLike----------->");
String likeName = "ph";
userList = userMapper.findWithLike(likeName);
System.out.println(userList);
} catch (Exception e) {
e.printStackTrace();
}
finally{
MybatisFactory.close(session);
}
}
}
3.多对一，一对多 关联的处理
3.1数据库建两表
USE mybatis;
CREATE TABLE tb_clazz(
id INT PRIMARY KEY AUTO_INCREMENT,
CODE VARCHAR(16)
);
CREATE TABLE tb_student(
id INT PRIMARY KEY AUTO_INCREMENT,
NAME VARCHAR(32),
sex VARCHAR(2),
age INT ,
clazz_id INT,
CONSTRAINT clazz_fk FOREIGN KEY (clazz_id) REFERENCES tb_clazz(id)
);
INSERT INTO tb_clazz(CODE) VALUES('12345');
INSERT INTO tb_clazz(CODE) VALUES('11122');
INSERT INTO tb_student(NAME,sex,age,clazz_id) VALUES('phf1','男',12,1);
INSERT INTO tb_student(NAME,sex,age,clazz_id) VALUES('phf2','男',13,1);
INSERT INTO tb_student(NAME,sex,age,clazz_id) VALUES('phf3','男',25,1);
INSERT INTO tb_student(NAME,sex,age,clazz_id) VALUES('phf4','男',24,2);
INSERT INTO tb_student(NAME,sex,age,clazz_id) VALUES('phf5','女',23,1);
INSERT INTO tb_student(NAME,sex,age,clazz_id) VALUES('phf6','男',26,2);
3.2 表映射类
package org.phf.pojo;
public class Student {
private Integer id;
private String name;
private String sex;
private Integer age;
//多对一
private Clazz clazz;
public Student() {
super();
// TODO Auto-generated constructor stub
}
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 String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
public Clazz getClazz() {
return clazz;
}
public void setClazz(Clazz clazz) {
this.clazz = clazz;
}
@Override
public String toString() {
return "Student [id=" + id + ", name=" + name + ", sex=" + sex
+ ", clazz=" + clazz + "]\n";
}
}package org.phf.pojo;
import java.util.List;
public class Clazz {
private Integer id;
private String code;
//一对多
private List studentList;
public Clazz() {
super();
// TODO Auto-generated constructor stub
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getCode() {
return code;
}
public void setCode(String code) {
this.code = code;
}
public List getStudentList() {
return studentList;
}
public void setStudentList(List studentList) {
this.studentList = studentList;
}
@Override
public String toString() {
return "Clazz [id=" + id + ", code=" + code + ", studentList=\n"
+ studentList + "]";
}
}
3.3 XXXMapper.xml和XXXMapper.java接口文件
package org.phf.mapping;
import org.phf.pojo.Student;
public interface StudentMapper {
Student find(Integer id);
}
package org.phf.mapping;
import org.phf.pojo.Clazz;
public interface ClazzMapper {
Clazz find(Integer id);
}
3.4 在mybatis-config.xml文件中增加配置
3.5 测试代码增加
@Test
public void testMulti()
{
SqlSession session = null;
try {
session = MybatisFactory.getSqlSession();
StudentMapper studentMapper = session.getMapper(StudentMapper.class);
System.out.println("<-----testMulti----Student--find by id------------>");
Student stu = studentMapper.find(1);
System.out.println(stu);
ClazzMapper clazzMapper = session.getMapper(ClazzMapper.class);
System.out.println("<-----testMulti---Clazz--find by id------------>");
Clazz clazz = clazzMapper.find(1);
System.out.println(clazz);
} catch (Exception e) {
e.printStackTrace();
}
finally{
MybatisFactory.close(session);
}
}