TiDB 和 Java 的简单 CRUD 应用程序

可以看到，JDBC 实现的代码略显冗余，需要自己管控错误处理逻辑，且不能很好的复用代码，并非最佳实践。

Mybatis 是当前比较流行的开源 Java 应用持久层框架，本文将以 Maven 插件的方式使用 MyBatis Generator 生成部分持久层代码。

进入目录 plain-java-mybatis：

cd plain-java-mybatis

目录结构如下所示：

.
├── Makefile
├── pom.xml
└── src
    └── main
        ├── java
        │   └── com
        │       └── pingcap
        │           ├── MybatisExample.java
        │           ├── dao
        │           │   └── PlayerDAO.java
        │           └── model
        │               ├── Player.java
        │               ├── PlayerMapper.java
        │               └── PlayerMapperEx.java
        └── resources
            ├── dbinit.sql
            ├── log4j.properties
            ├── mapper
            │   ├── PlayerMapper.xml
            │   └── PlayerMapperEx.xml
            ├── mybatis-config.xml
            └── mybatis-generator.xml

其中，自动生成的文件有：

• src/main/java/com/pingcap/model/Player.java：Player 实体类文件
• src/main/java/com/pingcap/model/PlayerMapper.java：Player Mapper 的接口文件
• src/main/resources/mapper/PlayerMapper.xml：Player Mapper 的 XML 映射，它是 Mybatis 用于生成 Player Mapper 接口的实现类的配置

这些文件的生成策略被写在了 mybatis-generator.xml 配置文件内，它是 Mybatis Generator 的配置文件，下面配置文件中添加了使用方法的说明：

<!DOCTYPE generatorConfiguration PUBLIC
 "-//mybatis.org//DTD MyBatis Generator Configuration 1.0//EN"
 "http://mybatis.org/dtd/mybatis-generator-config_1_0.dtd">

<generatorConfiguration>
    <!--
        <context/> entire document: https://mybatis.org/generator/configreference/context.html

        context.id: A unique identifier you like
        context.targetRuntime: Used to specify the runtime target for generated code.
            It has MyBatis3DynamicSql / MyBatis3Kotlin / MyBatis3 / MyBatis3Simple 4 selection to choice.
    -->
    <context id="simple" targetRuntime="MyBatis3">
        <!--
            <commentGenerator/> entire document: https://mybatis.org/generator/configreference/commentGenerator.html

            commentGenerator:
                - property(suppressDate): remove timestamp in comments
                - property(suppressAllComments): remove all comments
        -->
        <commentGenerator>
            <property name="suppressDate" value="true"/>
            <property name="suppressAllComments" value="true" />
        </commentGenerator>

        <!--
            <jdbcConnection/> entire document: https://mybatis.org/generator/configreference/jdbcConnection.html

            jdbcConnection.driverClass: The fully qualified class name for the JDBC driver used to access the database.
                Used mysql-connector-java:5.1.49, should specify JDBC is com.mysql.jdbc.Driver
            jdbcConnection.connectionURL: The JDBC connection URL used to access the database.
        -->
        <jdbcConnection driverClass="com.mysql.jdbc.Driver"
            connectionURL="jdbc:mysql://localhost:4000/test?user=root" />

        <!--
            <javaModelGenerator/> entire document: https://mybatis.org/generator/configreference/javaModelGenerator.html
            Model code file will be generated at ${targetProject}/${targetPackage}

            javaModelGenerator:
                - property(constructorBased): If it's true, generator will create constructor function in model
        -->
        <javaModelGenerator targetPackage="com.pingcap.model" targetProject="src/main/java">
            <property name="constructorBased" value="true"/>
        </javaModelGenerator>

        <!--
            <sqlMapGenerator/> entire document: https://mybatis.org/generator/configreference/sqlMapGenerator.html
            XML SQL mapper file will be generated at ${targetProject}/${targetPackage}
        -->
        <sqlMapGenerator targetPackage="." targetProject="src/main/resources/mapper"/>

        <!--
            <javaClientGenerator/> entire document: https://mybatis.org/generator/configreference/javaClientGenerator.html
            Java code mapper interface file will be generated at ${targetProject}/${targetPackage}

            javaClientGenerator.type (context.targetRuntime is MyBatis3):
                This attribute indicated Mybatis how to implement interface.
                It has ANNOTATEDMAPPER / MIXEDMAPPER / XMLMAPPER 3 selection to choice.
        -->
        <javaClientGenerator type="XMLMAPPER" targetPackage="com.pingcap.model" targetProject="src/main/java"/>

        <!--
            <table/> entire document: https://mybatis.org/generator/configreference/table.html

            table.tableName: The name of the database table.
            table.domainObjectName: The base name from which generated object names will be generated. If not specified, MBG will generate a name automatically based on the tableName.
            table.enableCountByExample: Signifies whether a count by example statement should be generated.
            table.enableUpdateByExample: Signifies whether an update by example statement should be generated.
            table.enableDeleteByExample: Signifies whether a delete by example statement should be generated.
            table.enableSelectByExample: Signifies whether a select by example statement should be generated.
            table.selectByExampleQueryId: This value will be added to the select list of the select by example statement in this form: "'<value>' as QUERYID".
        -->
        <table tableName="player" domainObjectName="Player"
               enableCountByExample="false" enableUpdateByExample="false"
               enableDeleteByExample="false" enableSelectByExample="false"
               selectByExampleQueryId="false"/>
    </context>
</generatorConfiguration>

mybatis-generator.xml 在 pom.xml 中，以 mybatis-generator-maven-plugin 插件配置的方式被引入：

<plugin>
    <groupId>org.mybatis.generator</groupId>
    <artifactId>mybatis-generator-maven-plugin</artifactId>
    <version>1.4.1</version>
    <configuration>
        <configurationFile>src/main/resources/mybatis-generator.xml</configurationFile>
        <verbose>true</verbose>
        <overwrite>true</overwrite>
    </configuration>

    <dependencies>
        <!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
        <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>5.1.49</version>
        </dependency>
    </dependencies>
</plugin>

在 Maven 插件内引入后，可删除旧的生成文件后，通过命令 mvn mybatis-generate 生成新的文件。或者你也可以使用已经编写好的 make 命令，通过 make gen 来同时删除旧文件，并生成新文件。

Player.java 是使用 Mybatis Generator 生成出的数据实体类文件，为数据库表在程序内的映射。Player 类的每个属性都对应着 player 表的一个字段。

package com.pingcap.model;

public class Player {
    private String id;

    private Integer coins;

    private Integer goods;

    public Player(String id, Integer coins, Integer goods) {
        this.id = id;
        this.coins = coins;
        this.goods = goods;
    }

    public Player() {
        super();
    }

    public String getId() {
        return id;
    }

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

    public Integer getCoins() {
        return coins;
    }

    public void setCoins(Integer coins) {
        this.coins = coins;
    }

    public Integer getGoods() {
        return goods;
    }

    public void setGoods(Integer goods) {
        this.goods = goods;
    }
}

PlayerMapper.java 是使用 Mybatis Generator 生成出的映射接口文件，它仅规定了接口，接口的实现类是由 Mybatis 来通过 XML 或注解自动生成的：

package com.pingcap.model;

import com.pingcap.model.Player;

public interface PlayerMapper {
    int deleteByPrimaryKey(String id);

    int insert(Player row);

    int insertSelective(Player row);

    Player selectByPrimaryKey(String id);

    int updateByPrimaryKeySelective(Player row);

    int updateByPrimaryKey(Player row);
}

PlayerMapper.xml 是使用 Mybatis Generator 生成出的映射 XML 文件，Mybatis 将使用这个文件自动生成 PlayerMapper 接口的实现类：

<?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.pingcap.model.PlayerMapper">
  <resultMap id="BaseResultMap" type="com.pingcap.model.Player">
    <constructor>
      <idArg column="id" javaType="java.lang.String" jdbcType="VARCHAR" />
      <arg column="coins" javaType="java.lang.Integer" jdbcType="INTEGER" />
      <arg column="goods" javaType="java.lang.Integer" jdbcType="INTEGER" />
    </constructor>
  </resultMap>
  <sql id="Base_Column_List">
    id, coins, goods
  </sql>
  <select id="selectByPrimaryKey" parameterType="java.lang.String" resultMap="BaseResultMap">
    select 
    <include refid="Base_Column_List" />
    from player
    where id = #{id,jdbcType=VARCHAR}
  </select>
  <delete id="deleteByPrimaryKey" parameterType="java.lang.String">
    delete from player
    where id = #{id,jdbcType=VARCHAR}
  </delete>
  <insert id="insert" parameterType="com.pingcap.model.Player">
    insert into player (id, coins, goods
      )
    values (#{id,jdbcType=VARCHAR}, #{coins,jdbcType=INTEGER}, #{goods,jdbcType=INTEGER}
      )
  </insert>
  <insert id="insertSelective" parameterType="com.pingcap.model.Player">
    insert into player
    <trim prefix="(" suffix=")" suffixOverrides=",">
      <if test="id != null">
        id,
      </if>
      <if test="coins != null">
        coins,
      </if>
      <if test="goods != null">
        goods,
      </if>
    </trim>
    <trim prefix="values (" suffix=")" suffixOverrides=",">
      <if test="id != null">
        #{id,jdbcType=VARCHAR},
      </if>
      <if test="coins != null">
        #{coins,jdbcType=INTEGER},
      </if>
      <if test="goods != null">
        #{goods,jdbcType=INTEGER},
      </if>
    </trim>
  </insert>
  <update id="updateByPrimaryKeySelective" parameterType="com.pingcap.model.Player">
    update player
    <set>
      <if test="coins != null">
        coins = #{coins,jdbcType=INTEGER},
      </if>
      <if test="goods != null">
        goods = #{goods,jdbcType=INTEGER},
      </if>
    </set>
    where id = #{id,jdbcType=VARCHAR}
  </update>
  <update id="updateByPrimaryKey" parameterType="com.pingcap.model.Player">
    update player
    set coins = #{coins,jdbcType=INTEGER},
      goods = #{goods,jdbcType=INTEGER}
    where id = #{id,jdbcType=VARCHAR}
  </update>
</mapper>

由于 Mybatis Generator 需要逆向生成源码，因此，数据库中需先行有此表结构，可使用 dbinit.sql 生成表结构：

USE test;
DROP TABLE IF EXISTS player;

CREATE TABLE player (
    `id` VARCHAR(36),
    `coins` INTEGER,
    `goods` INTEGER,
    PRIMARY KEY (`id`)
);

额外拆分接口 PlayerMapperEx 继承 PlayerMapper，并且编写与之匹配的 PlayerMapperEx.xml。避免直接更改 PlayerMapper.java 和 PlayerMapper.xml。这是为了规避 Mybatis Generator 的反复生成，影响到自行编写的代码。

在 PlayerMapperEx.java 中定义自行增加的接口：

package com.pingcap.model;

import java.util.List;

public interface PlayerMapperEx extends PlayerMapper {
    Player selectByPrimaryKeyWithLock(String id);

    List<Player> selectByLimit(Integer limit);

    Integer count();
}

在 PlayerMapperEx.xml 中定义映射规则：

<?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.pingcap.model.PlayerMapperEx">
  <resultMap id="BaseResultMap" type="com.pingcap.model.Player">
    <constructor>
      <idArg column="id" javaType="java.lang.String" jdbcType="VARCHAR" />
      <arg column="coins" javaType="java.lang.Integer" jdbcType="INTEGER" />
      <arg column="goods" javaType="java.lang.Integer" jdbcType="INTEGER" />
    </constructor>
  </resultMap>
  <sql id="Base_Column_List">
    id, coins, goods
  </sql>

  <select id="selectByPrimaryKeyWithLock" parameterType="java.lang.String" resultMap="BaseResultMap">
    select 
    <include refid="Base_Column_List" />
    from player
    where `id` = #{id,jdbcType=VARCHAR}
    for update
  </select>

  <select id="selectByLimit" parameterType="java.lang.Integer" resultMap="BaseResultMap">
    select
    <include refid="Base_Column_List" />
    from player
    limit #{id,jdbcType=INTEGER}
  </select>

  <select id="count" resultType="java.lang.Integer">
    select count(*) from player
  </select>

</mapper>

PlayerDAO.java 是程序用来管理数据对象的类。其中 DAO 是 Data Access Object 的缩写。在其中定义了一系列数据的操作方法，用于数据的写入。

package com.pingcap.dao;

import com.pingcap.model.Player;
import com.pingcap.model.PlayerMapperEx;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;

import java.util.List;
import java.util.function.Function;

public class PlayerDAO {
    public static class NotEnoughException extends RuntimeException {
        public NotEnoughException(String message) {
            super(message);
        }
    }

    // Run SQL code in a way that automatically handles the
    // transaction retry logic, so we don't have to duplicate it in
    // various places.
    public Object runTransaction(SqlSessionFactory sessionFactory, Function<PlayerMapperEx, Object> fn) {
        Object resultObject = null;
        SqlSession session = null;

        try {
            // open a session with autoCommit is false
            session = sessionFactory.openSession(false);

            // get player mapper
            PlayerMapperEx playerMapperEx = session.getMapper(PlayerMapperEx.class);

            resultObject = fn.apply(playerMapperEx);
            session.commit();
            System.out.println("APP: COMMIT;");
        } catch (Exception e) {
            if (e instanceof NotEnoughException) {
                System.out.printf("APP: ROLLBACK BY LOGIC; \n%s\n", e.getMessage());
            } else {
                System.out.printf("APP: ROLLBACK BY ERROR; \n%s\n", e.getMessage());
            }

            if (session != null) {
                session.rollback();
            }
        } finally {
            if (session != null) {
                session.close();
            }
        }

        return resultObject;
    }

    public Function<PlayerMapperEx, Object> createPlayers(List<Player> players) {
        return playerMapperEx -> {
            Integer addedPlayerAmount = 0;
            for (Player player: players) {
                playerMapperEx.insert(player);
                addedPlayerAmount ++;
            }
            System.out.printf("APP: createPlayers() --> %d\n", addedPlayerAmount);
            return addedPlayerAmount;
        };
    }

    public Function<PlayerMapperEx, Object> buyGoods(String sellId, String buyId, Integer amount, Integer price) {
        return playerMapperEx -> {
            Player sellPlayer = playerMapperEx.selectByPrimaryKeyWithLock(sellId);
            Player buyPlayer = playerMapperEx.selectByPrimaryKeyWithLock(buyId);

            if (buyPlayer == null || sellPlayer == null) {
                throw new NotEnoughException("sell or buy player not exist");
            }

            if (buyPlayer.getCoins() < price || sellPlayer.getGoods() < amount) {
                throw new NotEnoughException("coins or goods not enough, rollback");
            }

            int affectRows = 0;
            buyPlayer.setGoods(buyPlayer.getGoods() + amount);
            buyPlayer.setCoins(buyPlayer.getCoins() - price);
            affectRows += playerMapperEx.updateByPrimaryKey(buyPlayer);

            sellPlayer.setGoods(sellPlayer.getGoods() - amount);
            sellPlayer.setCoins(sellPlayer.getCoins() + price);
            affectRows += playerMapperEx.updateByPrimaryKey(sellPlayer);

            System.out.printf("APP: buyGoods --> sell: %s, buy: %s, amount: %d, price: %d\n", sellId, buyId, amount, price);
            return affectRows;
        };
    }

    public Function<PlayerMapperEx, Object> getPlayerByID(String id) {
        return playerMapperEx -> playerMapperEx.selectByPrimaryKey(id);
    }

    public Function<PlayerMapperEx, Object> printPlayers(Integer limit) {
        return playerMapperEx -> {
            List<Player> players = playerMapperEx.selectByLimit(limit);

            for (Player player: players) {
                System.out.println("\n[printPlayers]:\n" + player);
            }
            return 0;
        };
    }

    public Function<PlayerMapperEx, Object> countPlayers() {
        return PlayerMapperEx::count;
    }
}

MybatisExample 是 plain-java-mybatis 这个示例程序的主类。其中定义了入口函数：

package com.pingcap;

import com.pingcap.dao.PlayerDAO;
import com.pingcap.model.Player;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

import java.io.IOException;
import java.io.InputStream;
import java.util.Arrays;
import java.util.Collections;

public class MybatisExample {
    public static void main( String[] args ) throws IOException {
        // 1. Create a SqlSessionFactory based on our mybatis-config.xml configuration
        // file, which defines how to connect to the database.
        InputStream inputStream = Resources.getResourceAsStream("mybatis-config.xml");
        SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

        // 2. And then, create DAO to manager your data
        PlayerDAO playerDAO = new PlayerDAO();

        // 3. Run some simple examples.

        // Create a player who has 1 coin and 1 goods.
        playerDAO.runTransaction(sessionFactory, playerDAO.createPlayers(
                Collections.singletonList(new Player("test", 1, 1))));

        // Get a player.
        Player testPlayer = (Player)playerDAO.runTransaction(sessionFactory, playerDAO.getPlayerByID("test"));
        System.out.printf("PlayerDAO.getPlayer:\n    => id: %s\n    => coins: %s\n    => goods: %s\n",
                testPlayer.getId(), testPlayer.getCoins(), testPlayer.getGoods());

        // Count players amount.
        Integer count = (Integer)playerDAO.runTransaction(sessionFactory, playerDAO.countPlayers());
        System.out.printf("PlayerDAO.countPlayers:\n    => %d total players\n", count);

        // Print 3 players.
        playerDAO.runTransaction(sessionFactory, playerDAO.printPlayers(3));

        // 4. Getting further.

        // Player 1: id is "1", has only 100 coins.
        // Player 2: id is "2", has 114514 coins, and 20 goods.
        Player player1 = new Player("1", 100, 0);
        Player player2 = new Player("2", 114514, 20);

        // Create two players "by hand", using the INSERT statement on the backend.
        int addedCount = (Integer)playerDAO.runTransaction(sessionFactory,
                playerDAO.createPlayers(Arrays.asList(player1, player2)));
        System.out.printf("PlayerDAO.createPlayers:\n    => %d total inserted players\n", addedCount);

        // Player 1 wants to buy 10 goods from player 2.
        // It will cost 500 coins, but player 1 cannot afford it.
        System.out.println("\nPlayerDAO.buyGoods:\n    => this trade will fail");
        Integer updatedCount = (Integer)playerDAO.runTransaction(sessionFactory,
                playerDAO.buyGoods(player2.getId(), player1.getId(), 10, 500));
        System.out.printf("PlayerDAO.buyGoods:\n    => %d total update players\n", updatedCount);

        // So player 1 has to reduce the incoming quantity to two.
        System.out.println("\nPlayerDAO.buyGoods:\n    => this trade will success");
        updatedCount = (Integer)playerDAO.runTransaction(sessionFactory,
                playerDAO.buyGoods(player2.getId(), player1.getId(), 2, 100));
        System.out.printf("PlayerDAO.buyGoods:\n    => %d total update players\n", updatedCount);
    }
}

可以看到，JDBC 实现的代码略显冗余，需要自己管控错误处理逻辑，且不能很好的复用代码。并非最佳实践。

当前开源比较流行的 Java ORM 为 Hibernate，且 Hibernate 在版本 6.0.0.Beta2 及以后支持了 TiDB 方言。完美适配了 TiDB 的特性。因此，此处将以 6.0.0.Beta2 + 版本进行说明。

进入目录 plain-java-hibernate ：

cd plain-java-hibernate

目录结构如下所示：

.
├── Makefile
├── plain-java-hibernate.iml
├── pom.xml
└── src
    └── main
        ├── java
        │   └── com
        │       └── pingcap
        │           └── HibernateExample.java
        └── resources
            └── hibernate.cfg.xml

其中，hibernate.cfg.xml 为 Hibernate 配置文件，定义了：

<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
        "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
    <session-factory>

        <!-- Database connection settings -->
        <property name="hibernate.connection.driver_class">com.mysql.cj.jdbc.Driver</property>
        <property name="hibernate.dialect">org.hibernate.dialect.TiDBDialect</property>
        <property name="hibernate.connection.url">jdbc:mysql://localhost:4000/test</property>
        <property name="hibernate.connection.username">root</property>
        <property name="hibernate.connection.password"></property>
        <property name="hibernate.connection.autocommit">false</property>

        <!-- Required so a table can be created from the 'PlayerDAO' class -->
        <property name="hibernate.hbm2ddl.auto">create-drop</property>

        <!-- Optional: Show SQL output for debugging -->
        <property name="hibernate.show_sql">true</property>
        <property name="hibernate.format_sql">true</property>
    </session-factory>
</hibernate-configuration>

HibernateExample.java 是 plain-java-hibernate 这个示例程序的主体。使用 Hibernate 时，相较于 JDBC，这里仅需写入配置文件地址，Hibernate 屏蔽了创建数据库连接时，不同数据库差异的细节。

PlayerDAO 是程序用来管理数据对象的类。其中 DAO 是 Data Access Object 的缩写。其中定义了一系列数据的操作方法，用来提供数据的写入能力。相较于 JDBC， Hibernate 封装了大量的操作，如对象映射、基本对象的 CRUD 等，极大的简化了代码量。

PlayerBean 是数据实体类，为数据库表在程序内的映射。PlayerBean 的每个属性都对应着 player 表的一个字段。相较于 JDBC，Hibernate 的 PlayerBean 实体类为了给 Hibernate 提供更多的信息，加入了注解，用来指示映射关系。

package com.pingcap;

import jakarta.persistence.Column;
import jakarta.persistence.Entity;
import jakarta.persistence.Id;
import jakarta.persistence.Table;
import org.hibernate.JDBCException;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.hibernate.query.NativeQuery;
import org.hibernate.query.Query;

import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.function.Function;

@Entity
@Table(name = "player_hibernate")
class PlayerBean {
    @Id
    private String id;
    @Column(name = "coins")
    private Integer coins;
    @Column(name = "goods")
    private Integer goods;

    public PlayerBean() {
    }

    public PlayerBean(String id, Integer coins, Integer goods) {
        this.id = id;
        this.coins = coins;
        this.goods = goods;
    }

    public String getId() {
        return id;
    }

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

    public Integer getCoins() {
        return coins;
    }

    public void setCoins(Integer coins) {
        this.coins = coins;
    }

    public Integer getGoods() {
        return goods;
    }

    public void setGoods(Integer goods) {
        this.goods = goods;
    }

    @Override
    public String toString() {
        return String.format("    %-8s => %10s\n    %-8s => %10s\n    %-8s => %10s\n",
                "id", this.id, "coins", this.coins, "goods", this.goods);
    }
}

/**
 * Main class for the basic Hibernate example.
 **/
public class HibernateExample
{
    public static class PlayerDAO {
        public static class NotEnoughException extends RuntimeException {
            public NotEnoughException(String message) {
                super(message);
            }
        }

        // Run SQL code in a way that automatically handles the
        // transaction retry logic so we don't have to duplicate it in
        // various places.
        public Object runTransaction(Session session, Function<Session, Object> fn) {
            Object resultObject = null;

            Transaction txn = session.beginTransaction();
            try {
                resultObject = fn.apply(session);
                txn.commit();
                System.out.println("APP: COMMIT;");
            } catch (JDBCException e) {
                System.out.println("APP: ROLLBACK BY JDBC ERROR;");
                txn.rollback();
            } catch (NotEnoughException e) {
                System.out.printf("APP: ROLLBACK BY LOGIC; %s", e.getMessage());
                txn.rollback();
            }
            return resultObject;
        }

        public Function<Session, Object> createPlayers(List<PlayerBean> players) throws JDBCException {
            return session -> {
                Integer addedPlayerAmount = 0;
                for (PlayerBean player: players) {
                    session.persist(player);
                    addedPlayerAmount ++;
                }
                System.out.printf("APP: createPlayers() --> %d\n", addedPlayerAmount);
                return addedPlayerAmount;
            };
        }

        public Function<Session, Object> buyGoods(String sellId, String buyId, Integer amount, Integer price) throws JDBCException {
            return session -> {
                PlayerBean sellPlayer = session.get(PlayerBean.class, sellId);
                PlayerBean buyPlayer = session.get(PlayerBean.class, buyId);

                if (buyPlayer == null || sellPlayer == null) {
                    throw new NotEnoughException("sell or buy player not exist");
                }

                if (buyPlayer.getCoins() < price || sellPlayer.getGoods() < amount) {
                    throw new NotEnoughException("coins or goods not enough, rollback");
                }

                buyPlayer.setGoods(buyPlayer.getGoods() + amount);
                buyPlayer.setCoins(buyPlayer.getCoins() - price);
                session.persist(buyPlayer);

                sellPlayer.setGoods(sellPlayer.getGoods() - amount);
                sellPlayer.setCoins(sellPlayer.getCoins() + price);
                session.persist(sellPlayer);

                System.out.printf("APP: buyGoods --> sell: %s, buy: %s, amount: %d, price: %d\n", sellId, buyId, amount, price);
                return 0;
            };
        }

        public Function<Session, Object> getPlayerByID(String id) throws JDBCException {
            return session -> session.get(PlayerBean.class, id);
        }

        public Function<Session, Object> printPlayers(Integer limit) throws JDBCException {
            return session -> {
                NativeQuery<PlayerBean> limitQuery = session.createNativeQuery("SELECT * FROM player_hibernate LIMIT :limit", PlayerBean.class);
                limitQuery.setParameter("limit", limit);
                List<PlayerBean> players = limitQuery.getResultList();

                for (PlayerBean player: players) {
                    System.out.println("\n[printPlayers]:\n" + player);
                }
                return 0;
            };
        }

        public Function<Session, Object> countPlayers() throws JDBCException {
            return session -> {
                Query<Long> countQuery = session.createQuery("SELECT count(player_hibernate) FROM PlayerBean player_hibernate", Long.class);
                return countQuery.getSingleResult();
            };
        }
    }

    public static void main(String[] args) {
        // 1. Create a SessionFactory based on our hibernate.cfg.xml configuration
        // file, which defines how to connect to the database.
        SessionFactory sessionFactory
                = new Configuration()
                .configure("hibernate.cfg.xml")
                .addAnnotatedClass(PlayerBean.class)
                .buildSessionFactory();

        try (Session session = sessionFactory.openSession()) {
            // 2. And then, create DAO to manager your data.
            PlayerDAO playerDAO = new PlayerDAO();

            // 3. Run some simple examples.

            // Create a player who has 1 coin and 1 goods.
            playerDAO.runTransaction(session, playerDAO.createPlayers(Collections.singletonList(
                    new PlayerBean("test", 1, 1))));

            // Get a player.
            PlayerBean testPlayer = (PlayerBean)playerDAO.runTransaction(session, playerDAO.getPlayerByID("test"));
            System.out.printf("PlayerDAO.getPlayer:\n    => id: %s\n    => coins: %s\n    => goods: %s\n",
                    testPlayer.getId(), testPlayer.getCoins(), testPlayer.getGoods());

            // Count players amount.
            Long count = (Long)playerDAO.runTransaction(session, playerDAO.countPlayers());
            System.out.printf("PlayerDAO.countPlayers:\n    => %d total players\n", count);

            // Print 3 players.
            playerDAO.runTransaction(session, playerDAO.printPlayers(3));

            // 4. Explore more.

            // Player 1: id is "1", has only 100 coins.
            // Player 2: id is "2", has 114514 coins, and 20 goods.
            PlayerBean player1 = new PlayerBean("1", 100, 0);
            PlayerBean player2 = new PlayerBean("2", 114514, 20);

            // Create two players "by hand", using the INSERT statement on the backend.
            int addedCount = (Integer)playerDAO.runTransaction(session,
                    playerDAO.createPlayers(Arrays.asList(player1, player2)));
            System.out.printf("PlayerDAO.createPlayers:\n    => %d total inserted players\n", addedCount);

            // Player 1 wants to buy 10 goods from player 2.
            // It will cost 500 coins, but player 1 cannot afford it.
            System.out.println("\nPlayerDAO.buyGoods:\n    => this trade will fail");
            Integer updatedCount = (Integer)playerDAO.runTransaction(session,
                    playerDAO.buyGoods(player2.getId(), player1.getId(), 10, 500));
            System.out.printf("PlayerDAO.buyGoods:\n    => %d total update players\n", updatedCount);

            // So player 1 has to reduce the incoming quantity to two.
            System.out.println("\nPlayerDAO.buyGoods:\n    => this trade will success");
            updatedCount = (Integer)playerDAO.runTransaction(session,
                    playerDAO.buyGoods(player2.getId(), player1.getId(), 2, 100));
            System.out.printf("PlayerDAO.buyGoods:\n    => %d total update players\n", updatedCount);
        } finally {
            sessionFactory.close();
        }
    }
}

在 Gitpod Playground 中尝试 JDBC：现在就试试

使用 JDBC 时，需手动初始化数据库表。若你本地已经安装了 mysql-client，且使用本地集群，可直接在 plain-java-mybatis 目录下通过 make prepare 运行：

make prepare

或直接执行：

mysql --host 127.0.0.1 --port 4000 -u root < src/main/resources/dbinit.sql

若你不使用本地集群，或未安装 mysql-client，请直接登录你的集群，并运行 src/main/resources/dbinit.sql 文件内的 SQL 语句。

在 Gitpod Playground 中尝试 Hibernate: 现在就试试

无需手动初始化表。

若你使用非本地默认集群、TiDB Cloud 或其他远程集群，更改 mybatis-config.xml 内关于 dataSource.url、dataSource.username、dataSource.password 的参数：

<?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>
    <settings>
        <setting name="cacheEnabled" value="true"/>
        <setting name="lazyLoadingEnabled" value="false"/>
        <setting name="aggressiveLazyLoading" value="true"/>
        <setting name="logImpl" value="LOG4J"/>
    </settings>

    <typeAliases>
        <package name="com.pingcap.dao"/>
    </typeAliases>

    <environments default="development">
        <environment id="development">
            <!-- JDBC transaction manager -->
            <transactionManager type="JDBC"/>
            <!-- Database pool -->
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://127.0.0.1:4000/test"/>
                <property name="username" value="root"/>
                <property name="password" value=""/>
            </dataSource>
        </environment>
    </environments>

    <mappers>
        <mapper resource="mapper/PlayerMapper.xml"/>
        <mapper resource="mapper/PlayerMapperEx.xml"/>
    </mappers>

</configuration>

若你设定的密码为 123456，而且从 TiDB Cloud 得到的连接字符串为：

mysql --connect-timeout 15 -u root -h tidb.e049234d.d40d1f8b.us-east-1.prod.aws.tidbcloud.com -P 4000 -p

那么此处应将配置文件中 dataSource 节点内更改为：

<?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">

        ...
            <!-- Database pool -->
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://tidb.e049234d.d40d1f8b.us-east-1.prod.aws.tidbcloud.com:4000/test"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        ...

</configuration>

若你使用非本地默认集群、TiDB Cloud 或其他远程集群，更改 hibernate.cfg.xml 内关于 hibernate.connection.url、hibernate.connection.username、hibernate.connection.password 的参数：

<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
        "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
    <session-factory>

        <!-- Database connection settings -->
        <property name="hibernate.connection.driver_class">com.mysql.cj.jdbc.Driver</property>
        <property name="hibernate.dialect">org.hibernate.dialect.TiDBDialect</property>
        <property name="hibernate.connection.url">jdbc:mysql://localhost:4000/test</property>
        <property name="hibernate.connection.username">root</property>
        <property name="hibernate.connection.password"></property>
        <property name="hibernate.connection.autocommit">false</property>

        <!-- Required so a table can be created from the 'PlayerDAO' class -->
        <property name="hibernate.hbm2ddl.auto">create-drop</property>

        <!-- Optional: Show SQL output for debugging -->
        <property name="hibernate.show_sql">true</property>
        <property name="hibernate.format_sql">true</property>
    </session-factory>
</hibernate-configuration>

若你设定的密码为 123456，而且从 TiDB Cloud 得到的连接字符串为：

mysql --connect-timeout 15 -u root -h tidb.e049234d.d40d1f8b.us-east-1.prod.aws.tidbcloud.com -P 4000 -p

那么此处应将配置文件更改为：

<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
        "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
    <session-factory>

        <!-- Database connection settings -->
        <property name="hibernate.connection.driver_class">com.mysql.cj.jdbc.Driver</property>
        <property name="hibernate.dialect">org.hibernate.dialect.TiDBDialect</property>
        <property name="hibernate.connection.url">jdbc:mysql://tidb.e049234d.d40d1f8b.us-east-1.prod.aws.tidbcloud.com:4000/test</property>
        <property name="hibernate.connection.username">root</property>
        <property name="hibernate.connection.password">123456</property>
        <property name="hibernate.connection.autocommit">false</property>

        <!-- Required so a table can be created from the 'PlayerDAO' class -->
        <property name="hibernate.hbm2ddl.auto">create-drop</property>

        <!-- Optional: Show SQL output for debugging -->
        <property name="hibernate.show_sql">true</property>
        <property name="hibernate.format_sql">true</property>
    </session-factory>
</hibernate-configuration>

运行 make，这是以下四个操作的组合：

• 创建表 (make prepare)：

  mysql --host 127.0.0.1 --port 4000 -u root < src/main/resources/dbinit.sql
  mysql --host 127.0.0.1 --port 4000 -u root -e "TRUNCATE test.player"
  

• 清理并构建 (make gen)：

  rm -f src/main/java/com/pingcap/model/Player.java
  rm -f src/main/java/com/pingcap/model/PlayerMapper.java
  rm -f src/main/resources/mapper/PlayerMapper.xml
  mvn mybatis-generator:generate
  

• 清理并构建 (make build)：mvn clean package

• 运行 (make run)：java -jar target/plain-java-mybatis-0.0.1-jar-with-dependencies.jar

你也可以单独运行这四个 make 命令或原生命令。

运行 make，这是以下两个操作的组合：

• 清理并构建 (make build)：mvn clean package
• 运行 (make run)：java -jar target/plain-java-hibernate-0.0.1-jar-with-dependencies.jar

你也可以单独运行这两个 make 命令或原生命令。

Hibernate 预期输出