Java程式設計：MyBatis讀取資料庫資料

1、檔案結構

一共涉及3個檔案夾8個檔案，心累…

注意config檔案夾和lib檔案夾需要設定為資源檔案夾，不然找不到檔案

2、依賴下載下傳

放入lib檔案夾

mybatis： 

https://github.com/mybatis/mybatis-3/releases

mysql-connector: 

https://dev.mysql.com/downloads/connector/j/

3、資料準備

demo的資料庫下有一個names的資料表，字段類型和資料如下

mysql> desc names;
+-------+--------------+------+-----+---------+----------------+
| Field | Type         | Null | Key | Default | Extra          |
+-------+--------------+------+-----+---------+----------------+
| id    | int(10)      | NO   | PRI | NULL    | auto_increment |
| name  | varchar(255) | YES  | UNI | NULL    |                |
| age   | int(10)      | YES  |     | NULL    |                |
+-------+--------------+------+-----+---------+----------------+

mysql> select * from names;
+----+--------+------+
| id | name   | age  |
+----+--------+------+
|  2 | 大紅   |   27 |
|  3 | 大壯   |   24 |
|  4 | 秀英   |   25 |
+----+--------+------+      

4、Person類編寫

其實就是一個普通的java類

Person.class

public class Person {
    private Integer id;
    private  String name;
    private Integer age;

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String toString(){
        return "[Person] id: "+ id + " name: " + name + " age :"+ age;
    }
}
      

5、配置映射器

方式一 檔案配置映射器：

映射接口 PersonMapper.class

public interface PersonMapper {
    public Person getPersonById(Integer id);
}
      

映射檔案 PersonMapper.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">

<!--
1.PersonMapper為命名空間,為映射接口的全類名
2.id為唯一辨別，與PersonMapper接口中的對應方法名相同
3.resultType為查詢後的傳回類型
4.#{id}指從傳遞過來的參數中取出id值
-->
<mapper namespace="PersonMapper">
    <select id="getPersonById" resultType="Person">
    select id,name, age from names where id = #{id}
  </select>
</mapper>      

方式二 注解配置映射器：

PersonMapperAnnoation.class

import org.apache.ibatis.annotations.Select;

public interface PersonMapperAnnoation {
        @Select("select id, name, age from names where id = #{id}")
        public Person getPersonById(Integer id);
}
      

這樣看來，方式2更為簡潔和清晰

6、資料庫配置填入資料庫的位址，賬号，密碼

配置映射器，可以使用兩種方式resource 和 class

<?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>
    <environments default="development">
        <environment id="development">
            <!-- 配置事務管理器，采用的是JDBC的管理器方式 -->
            <transactionManager type="JDBC"/>
            <!--  POOLED代表采用MyBatis内部提供的連接配接池方式 -->
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/demo"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>
    <!--  引入映射器 包名+檔案名-->
    <mappers>
        <mapper resource="PersonMapper.xml"/>
        <mapper class="PersonMapperAnnoation"/>
    </mappers>
</configuration>      

7、代碼測試

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

public class mybatisDemo {
    public static void main(String[] args) throws IOException{

        //1.根據MyBatis的配置檔案，即mybatis-config.xml建立SqlSessionFactory
        SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
        //2.擷取session執行個體開啟會話，其能直接執行*已經映射的SQL語句*
        SqlSession session = sqlSessionFactory.openSession();
        try {
            // 方式1 查詢
            //3.擷取接口的實作類對象
            PersonMapper personMapper = session.getMapper(PersonMapper.class);
            //4.執行查詢操作
            Person person = personMapper.getPersonById(2);
            System.out.println(person);
            
            // 方式2 查詢
            //3.擷取接口的實作類對象
            PersonMapperAnnoation personMapperAnnoation = session.getMapper(PersonMapperAnnoation.class);
            //4.執行查詢操作
            Person person1 = personMapperAnnoation.getPersonById(2);
            System.out.println(person1);

        } finally {
            //4.關閉會話session
            session.close();
        }
    }

    //根據MyBatis的配置檔案，即mybatis-config.xml建立SqlSessionFactory
    public static SqlSessionFactory getSqlSessionFactory() throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        return sqlSessionFactory;
    }

}

/*
兩種方式都能查到資料
[Person] id: 2 name: 大紅 age :27
[Person] id: 2 name: 大紅 age :27
*/      

參考

（二）MyBatis學習筆記-HelloWorld