Java如何创建MyBatis SqlSession对象？

要创建一个，SqlSession您可以使用SqlSessionFactoryclassopenSession()方法。此方法提供了一些可以配置会话属性的重载方法。例如，我们可以配置会话的自动提交模式和事务隔离级别。

package org.nhooo.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.nhooo.example.mybatis.domain.Record;

import java.io.IOException;
import java.io.Reader;

public class SqlSessionDemo {
    public static void main(String[] args) throws IOException {
        SqlSessionDemo demo = new SqlSessionDemo();

        // 建立一个SqlSessionFactory。
        SqlSessionFactory factory = demo.getSessionFactory();

        // 通过使用factory.openSession()方法创建一个SqlSession。
        // 在以下情况下，使用try-with-resources块是一个好习惯
        //使用SqlSession。会话将自动
        // 完成工作后关闭。
        try (SqlSession session = factory.openSession()) {
            Record record = session.selectOne("getRecord", 1L);
            System.out.println("Record = " + record);
        }
    }

    /**
     * Build an SqlSessionFactory.
     *
     * @return an SqlSessionFactory.
     * @throws IOException when fail to read the configuration file.
     */
    private SqlSessionFactory getSessionFactory() throws IOException {
        Reader reader = Resources.getResourceAsReader("configuration.xml");
        SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
        return builder.build(reader);
    }
}

以下是配置，映射器和POJO。

• configuration.xml

<?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.nhooo.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/musicdb"/>
                <property name="username" value="root"/>
                <property name="password" value=""/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="org/nhooo/example/mybatis/mapper/RecordMapper.xml"/>
    </mappers>
</configuration>

• RecordMapper.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">
<mapper namespace="org.nhooo.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="java.lang.Long" resultMap="recordResultMap">
        SELECT
            id,
            title,
            release_date,
            artist_id,
            label_id
        FROM records
        WHERE id = #{id}
    </select>
</mapper>

• Record.java

package org.nhooo.example.mybatis.domain;

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

public class Record implements Serializable {
    private Long id;
    private String title;
    private Date releaseDate;
    private Long artistId;
    private Long labelId;

    public Long getId() {
        return id;
    }

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

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public Date getReleaseDate() {
        return releaseDate;
    }

    public void setReleaseDate(Date releaseDate) {
        this.releaseDate = releaseDate;
    }

    public Long getArtistId() {
        return artistId;
    }

    public void setArtistId(Long artistId) {
        this.artistId = artistId;
    }

    public Long getLabelId() {
        return labelId;
    }

    public void setLabelId(Long labelId) {
        this.labelId = labelId;
    }

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

上面的代码的目录结构是：

├── pom.xml
└── src
    └── main
        ├── java
        │   └── org
        │       └── nhooo
        │           └── example
        │               └── mybatis
        │                   ├── SqlSessionDemo.java
        │                   └── domain
        │                       └── Record.java
        └── resources
            ├── configuration.xml
            └── org
                └── nhooo
                   └── example
                        └── mybatis
                            └── mapper
                                └── RecordMapper.xml

Maven依赖

<!-- https://search.maven.org/remotecontent?filepath=org/mybatis/mybatis/3.5.0/mybatis-3.5.0.jar -->
<dependency>
  <groupId>org.mybatis</groupId>
  <artifactId>mybatis</artifactId>
  <version>3.5.0</version>
</dependency>
<!-- https://search.maven.org/remotecontent?filepath=mysql/mysql-connector-java/5.1.47/mysql-connector-java-5.1.47.jar -->
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>5.1.47</version>
</dependency>