MyBatis Example

Firstly, give you a simple example as a tutorial, then you will get an another example to explain the detail usage:

In this examples you will see how to create or define a data mapper using the MyBatis. The mapper will communicate our application with the underlying databases where the data is stored. MyBatis data mapper is defined as an interface object. We can either use annotations or the xml mapper to define our database query.

In the first steps we will create a domain object, a simple pojo to store our data in the object world. The attributes / fields of our pojo resemble the structure of our records table in the database.

package org.kodejava.example.mybatis.domain;

import java.io.Serializable;
import java.util.Date;

public class Record implements Serializable {
    private Integer id;
    private String title;
    private Date releaseDate;
    private Integer artistId;
    private Integer labelId;
    private Date created;
    private Date modified;

    public Record() {
    }

    //
    // Define the getters and setters for our pojo.
    //
    // ...
    // ...
    // ...

    @Override
    public String toString() {
        return "Record{" +
                "id=" + id +
                ", title='" + title + "'" +
                ", releaseDate=" + releaseDate +
                ", artistId=" + artistId +
                ", labelId=" + labelId +
                "}";
    }
}

Next we define the mapper interface code, we’ll create a RecordMapper.java file that contains a method to get data from the table. At this time the interface will be as the following:

package org.kodejava.example.mybatis.persistence;

import org.kodejava.example.mybatis.domain.Record;

public interface RecordMapper {
    /**
     * Get a single Record from the database based on the record
     * identified.
     * 
     * @param id record identifier.
     * @return a record object.
     */
    Record getRecord(int id);
}

After create the ResultMapper.java interface we create a RecordMapper.xml file that defines the queries used by our mapper. Here is how it looks like:

<?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="org.kodejava.example.mybatis.persistence.RecordMapper">

    <resultMap id="recordResultMap" type="record">
        <result column="release_date" property="releaseDate"/>
        <result column="artist_id" property="artistId"/>
        <result column="label_id" property="labelId"/>
    </resultMap>

    <select id="getRecord" parameterType="int" resultMap="recordResultMap">
        SELECT
            id,
            title,
            release_date,
            artist_id,
            label_id,
            created,
            modified
        FROM records
        WHERE id = #{id}
    </select>
</mapper>

To tell MyBatis about our mapper we need to define the mapper inside MyBatis configuration file. We register the mapper inside the <mappers> element of the configuration file.

<?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>
    <typeAliases>
        <typeAlias alias="record" type="org.kodejava.example.mybatis.domain.Record"/>
    </typeAliases>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost/mediadb"/>
                <property name="username" value="root"/>
                <property name="password" value="welcome"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="org/kodejava/example/mybatis/persistence/RecordMapper.xml"/>
    </mappers>
</configuration>

Finally, we create a simple application to use the data mapper to get record data from the database.

package org.kodejava.example.mybatis;

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.kodejava.example.mybatis.domain.Record;
import org.kodejava.example.mybatis.persistence.RecordMapper;

import java.io.Reader;

public class MediaClient {
    public static void main(String[] args) throws Exception {
        String resource = "org/kodejava/example/mybatis/Configuration.xml";
        Reader reader = Resources.getResourceAsReader(resource);

        SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
        SqlSessionFactory factory = builder.build(reader);

        SqlSession session = factory.openSession();
        try {
            RecordMapper mapper = session.getMapper(RecordMapper.class);
            Record record = mapper.getRecord(1);
            System.out.println("Record = " + record);
        } finally {
            session.close();
        }
    }
}

 

在SSH框架盛行的时代，ORM和持久层框架都不断响彻在耳边，今天小编就带领大家一起来认识另一种持久层框架；

一、基本概况

        MyBatis是一个支持普通SQL查询，存储过程和高级映射的优秀持久层框架。MyBatis可以使用简单的XML或注解用于配置和原始映射，将接口和Java的POJO对象映射成数据库中的记录。

框架图如下;

二、入门教程（使用mysql的数据库）

1. 搭建开发环境：

♔  创建一个普通的Java项目,如下图所示：

                         

♔  添加数据库和mybatis的jar包;

♔创建数据库，并建立数据表：

2. 实例-- 查询用户表中姓名为“小明”的模糊查询

  ✎ 在src中建立数据库的配置文件（db.properties）和日志的配置文件（log4j.properties）,并创建用户的实体类（User.java）

     db.properties

log4j.properties:

 User.java：

   ✎   然后建立系统的映射文件sqlMapConfig.xml(用来加载映射文件Mapper)：

   ✎ 在上述文件的路径“cn.itcast.mybatis.mapper”下建立用户的实体文件(UserMapper.java)和实体映射文件(UserMapper.xml);

       UserMapper.java（主要是mapper的代理接口）

      UserMapper的实体映射文件（编辑程序功能用到的sql语句）

PS：【与hibernate框架中的层结构一样都需要dao和daoImpl，这里dao和daoImpl就不再赘述】：

✎上述的准备工作都准备完毕之后，我们建立一个单元测试代码如下;

 到这里，使用mybatis+ mysql 实现模糊查询的功能就实现了，有兴趣的可以动手尝试一下；

三、总结

         mybatis是Apache下的顶级项目，是一个持久层框架，是一个不完全的ORM框架；

        mybatis使得程序将主要精力放在了sql上，它通过自身提供的映射方式，自由且灵活地生成满足程序需要的sql语句（半自动化，大部分需要程序员自己编写）;

        mybatis可以将向PreparedStatement中输入的参数自动进行输入映射，将查询结果集灵活映射成Java对象（输出映射）；