1.示例項目目錄:
2.相關接口和映射文件之間的規則
(1) 在mapper.xml中將namespace設置爲對應的mapper.java(Dao接口)的全限定名 。如:
(2) 將mapper.java接口的方法名和mapper.xml中statement的id保持一致。
(3) 將mapper.java接口的方法輸入參數類型和mapper.xml中statement的parameterType保持一致
(4) 將mapper.java接口的方法輸出 結果類型和mapper.xml中statement的resultType保持一致
3.Dao 接口不需要實現類
MyBatis在採用面向接口編程時,採用實體+接口+映射文件的方式。其中接口是不需要實現類的。
因爲Mybatis 提供了 Mapper接口的代理對象(mybatis通過JDK的動態代理方式,在啓動加載配置文件時,根據配置mapper的xml去生成Dao的實現,session.getMapper()使用了代理,當調用一次此方法,都會產生一個代理class的instance。),在執行 Mapper接口方法時,實際執行的是Mybatis的代理對象,代理對象在 invoke 方法內獲取 Mapper接口類全名+方法全名 作爲statement的ID,然後通過ID去Statement匹配註冊的SQL,然後使用 SqlSession 執行這個 SQL。所以,這也解釋了爲什麼Mybatis映射文件需要 namespace 和 id , 前者是類全名,後者是方法名。
4.具體示例
User類
package com.mybatisstudy.model;
public class User {
private int id;
private String name;
private String sex;
private int age;
public User() {
super();
}
public User(String name, String sex, int age) {
super();
this.name = name;
this.sex = sex;
this.age = age;
}
public User(int id, String name, String sex, int age) {
super();
this.id = id;
this.name = name;
this.sex = sex;
this.age = age;
}
public int getId() {
return id;
}
public void setId(int 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 int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@Override
public String toString() {
return "[id:" + id + ",name:" + name + ",sex:" + sex + ",age:" + age + "]";
}
}
userMapper.xml(實體映射文件)
<?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.mybatisstudy.dao.IUserDao">
<select id="selectAllUser"
resultType="com.mybatisstudy.model.User">
SELECT * FROM user ;
</select>
<select id="selectUserById" parameterType="int"
resultType="com.mybatisstudy.model.User">
SELECT * FROM user where id = #{id} ;
</select>
<insert id="addUser" parameterType="com.mybatisstudy.model.User">
INSERT INTO user(id,name,sex,age) VALUES(#{id},#{name},#{sex},#{age});
</insert>
<delete id="deleteUserById" parameterType="com.mybatisstudy.model.User">
DELETE FROM user WHERE id=#{id};
</delete>
<update id="updateUser" parameterType="com.mybatisstudy.model.User">
UPDATE user SET age=#{age} ,name=#{name} WHERE id=#{id}
</update>
</mapper>
IUserDao.java(Dao 接口)
package com.mybatisstudy.dao;
import java.util.List;
import com.mybatisstudy.model.User;
public interface IUserDao {
public List<User> selectAllUser();
public User selectUserById(int id);
public int addUser(User user);
public int deleteUserById(int id);
public int updateUser(User user);
}
TestUser.java(單元測試類)
package com.mybatisstudy.test;
import static org.junit.jupiter.api.Assertions.*;
import java.util.List;
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 org.junit.jupiter.api.AfterAll;
import org.junit.jupiter.api.AfterEach;
import org.junit.jupiter.api.BeforeAll;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import org.junit.Assert;
import com.mybatisstudy.dao.IUserDao;
import com.mybatisstudy.model.User;
class TestUser {
static SqlSessionFactory factory;
static SqlSession session;
IUserDao userDao;
@BeforeAll
static void setUpBeforeClass() throws Exception {
String resource = "mybatisconf.xml";
factory = new SqlSessionFactoryBuilder().build(Resources.getResourceAsStream(resource));
session = factory.openSession();
}
@AfterAll
static void tearDownAfterClass() throws Exception {
if (session != null) {
session.close();
}
session = null;
factory = null;
}
@BeforeEach
void setUp() throws Exception {
}
@AfterEach
void tearDown() throws Exception {
}
@Test
void testSelectAllUser() {
// 採用了實體+接口+映射文件的方式,在IUserDao中並沒有實現selectAllUser方法,而在映射文件中進行了實現
IUserDao userDao = session.getMapper(IUserDao.class);
List<User> users = userDao.selectAllUser();
System.out.println(users);
}
@Test
void testSelectUserById() {
IUserDao userDao = session.getMapper(IUserDao.class);
int userId = 1001;
User user = userDao.selectUserById(userId);
System.out.println(user);
}
@Test
void testAddUser() {
IUserDao userDao = session.getMapper(IUserDao.class);
User user = new User(1003, "小杰", "男", 20);
int line = userDao.addUser(user);
// 使用斷言
// assertEquals 如果預期值與真實值相等,則運行success,反之Failure
Assert.assertEquals(1, line);
}
@Test
void testUpdateUser() {
IUserDao userDao = session.getMapper(IUserDao.class);
User user = new User(1003, "小明", "男", 21);
int line = userDao.updateUser(user);
Assert.assertEquals(1, line);
}
@Test
void testDeleteUserById() {
IUserDao userDao = session.getMapper(IUserDao.class);
int line = userDao.deleteUserById(1003);
Assert.assertEquals(1, line);
}
}
mybatisconf.xml(MyBatis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>
<!-- 引用並使用db.properties -->
<properties resource="db.properties" />
<!-- environments:信息配置的是連接數據庫的(數據源的)一些參數,如用戶名,密碼等,MyBatis數據庫操作的session就是根據這些信息初始化的-->
<environments default="development">
<environment id="development">
<transactionManager type="JDBC" />
<!-- 數據源配置 -->
<dataSource type="POOLED">
<!-- 數據庫驅動 -->
<property name="driver" value="${driver}" />
<!-- 數據庫連接URL -->
<property name="url" value="${url}"/>
<!-- 數據庫用戶名和密碼 -->
<property name="username" value="${username}" />
<property name="password" value="${password}" />
</dataSource>
</environment>
</environments>
<!-- mappers:配置的是一個個Mapper文件,這些文件來約束數據庫的信息(Relationship) 和 對象(Object)的信息映射(Mapper);它負責完成對象和數據庫表的映射,是ORM最具體的配置-->
<mappers>
<!-- 配置實體映射文件 -->
<mapper resource="com/mybatisstudy/dao/userMapper.xml" />
</mappers>
</configuration>
db.properties(數據庫配置信息)
driver=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/mybatisstudy?useUnicode=true&characterEncoding=utf8
username=root
password=