MyBatis深入(1)-调试环境搭建

依赖工具

• Maven
• Git
• JDK1.8
• Intellij IDEA

源码拉取

直接从官方仓库 Fork 到自己的仓库，Fork 出来之后，在学习源码的过程中我们可以方便的写一些注释，自由的提交。

这里我 Fork 出来的 Mybatis 版本是 3.5.2-SNAPSHOT 。

调试

调试 MyBatis 源码非常简单，只需要打开 org.apache.ibatis.autoconstructor.AutoConstructorTest 单元测试类，运行任意一个方法即可。该类所在的包整体结构如下：

下面对该包中的结构做下介绍。

mybatis-config.xml

Mybatis 的配置文件，内容如下：

<!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">
            <!-- 配置事务管理 -->
            <transactionManager type="JDBC">
                <property name="" value=""/>
            </transactionManager>
            <!-- 配置数据源  -->
            <dataSource type="UNPOOLED">
                <property name="driver" value="org.hsqldb.jdbcDriver"/>
                <property name="url" value="jdbc:hsqldb:mem:automapping"/>
                <property name="username" value="sa"/>
            </dataSource>
        </environment>
    </environments>

    <!-- 扫描 Mapper 文件  -->
    <mappers>
        <mapper resource="org/apache/ibatis/autoconstructor/AutoConstructorMapper.xml"/>
    </mappers>
</configuration>

• 在 <environments /> 标签中，配置了事务管理和数据源。考虑到减少外部依赖，所以使用了 HSQLDB 。
• 在 <mappers /> 标签中，配置了需要扫描的 Mapper 文件。目前，仅仅扫描 AutoConstructorMapper.xml 文件。

AutoConstructorMapper.xml

Mapper 配置文件，代码如下：

<!DOCTYPE mapper
    PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
    "http://mybatis.org/dtd/mybatis-3-mapper.dtd">

<mapper namespace="org.apache.ibatis.autoconstructor.AutoConstructorMapper">
</mapper>

AutoConstructorMapper

Mapper 文件，对应上述配置文件，代码如下：

package org.apache.ibatis.autoconstructor;

import org.apache.ibatis.annotations.Select;

import java.util.List;

public interface AutoConstructorMapper {
  @Select("SELECT * FROM subject WHERE id = #{id}")
  PrimitiveSubject getSubject(final int id);

  @Select("SELECT * FROM subject")
  List<PrimitiveSubject> getSubjects();

  @Select("SELECT * FROM subject")
  List<AnnotatedSubject> getAnnotatedSubjects();

  @Select("SELECT * FROM subject")
  List<BadSubject> getBadSubjects();

  @Select("SELECT * FROM extensive_subject")
  List<ExtensiveSubject> getExtensiveSubject();
}

这里其实并没有用到上述的 AutoConstructorMapper.xml Mapper 配置文件，而是直接使用注解 SQL 的方式。

CreateDB.sql

用于单元测试里，初始化数据库的数据。如下：

DROP TABLE subject
IF EXISTS;

DROP TABLE extensive_subject
IF EXISTS;

CREATE TABLE subject (
  id     INT NOT NULL,
  name   VARCHAR(20),
  age    INT NOT NULL,
  height INT,
  weight INT,
  active BIT,
  dt     TIMESTAMP
);

CREATE TABLE extensive_subject (
  aByte      TINYINT,
  aShort     SMALLINT,
  aChar      CHAR,
  anInt      INT,
  aLong      BIGINT,
  aFloat     FLOAT,
  aDouble    DOUBLE,
  aBoolean   BIT,
  aString    VARCHAR(255),
  anEnum     VARCHAR(50),
  aClob      LONGVARCHAR,
  aBlob      LONGVARBINARY,
  aTimestamp TIMESTAMP
);

INSERT INTO subject VALUES
  (1, 'a', 10, 100, 45, 1, CURRENT_TIMESTAMP),
  (2, 'b', 10, NULL, 45, 1, CURRENT_TIMESTAMP),
  (2, 'c', 10, NULL, NULL, 0, CURRENT_TIMESTAMP);

INSERT INTO extensive_subject
VALUES
  (1, 1, 'a', 1, 1, 1, 1.0, 1, 'a', 'AVALUE', 'ACLOB', 'aaaaaabbbbbb', CURRENT_TIMESTAMP),
  (2, 2, 'b', 2, 2, 2, 2.0, 2, 'b', 'BVALUE', 'BCLOB', '010101010101', CURRENT_TIMESTAMP),
  (3, 3, 'c', 3, 3, 3, 3.0, 3, 'c', 'CVALUE', 'CCLOB', '777d010078da', CURRENT_TIMESTAMP);

• 创建了 subject 表，并初始化三条数据。
• 创建了 extensive_subject 表，并初始化三条数据。

POJO

在 AutoConstructorMapper 中，我们可以看到有四个 POJO 类。但是，从 CreateDB.sql 中，实际只有两个表。这个是为什么呢？继续往下看噢。

AnnotatedSubject

对应 Subject 表，内容如下：

ackage org.apache.ibatis.autoconstructor;

import org.apache.ibatis.annotations.AutomapConstructor;

public class AnnotatedSubject {

    private final int id;
    private final String name;
    private final int age;
    private final int height;
    private final int weight;

    public AnnotatedSubject(final int id, final String name, final int age, final int height, final int weight) {
        this.id = id;
        this.name = name;
        this.age = age;
        this.height = height;
        this.weight = weight;
    }

    @AutomapConstructor
    public AnnotatedSubject(final int id, final String name, final int age, final Integer height, final Integer weight) {
        this.id = id;
        this.name = name;
        this.age = age;
        this.height = height == null ? 0 : height;
        this.weight = weight == null ? 0 : weight;
    }
}

@AutomapConstructor 注解，表示在 MyBatis 查询后使用该构造方法来创建 AnnotatedSubject 对象。

PrimitiveSubject

对应的也是 Subject 表。

package org.apache.ibatis.autoconstructor;

import java.util.Date;

public class PrimitiveSubject {

    private final int id;
    private final String name;
    private final int age;
    private final int height;
    private final int weight;
    private final boolean active;
    private final Date dt;

    public PrimitiveSubject(final int id, final String name, final int age, final int height, final int weight, final boolean active, final Date dt) {
        this.id = id;
        this.name = name;
        this.age = age;
        this.height = height;
        this.weight = weight;
        this.active = active;
        this.dt = dt;
    }
}

和 AnnotatedSubject 不同，在其构造方法上， weight 和 height 方法参数的类型是 int ，而不是 Integer 。那么，如果 Subject 表中的记录，这两个字段为 NULL 时，创建 PrimitiveSubject 对象会报错。

BadSubject

依旧对应 Subject 表。

package org.apache.ibatis.autoconstructor;

public class BadSubject {

    private final int id;
    private final String name;
    private final int age;
    private final Height height;
    private final Double weight;

    public BadSubject(final int id, final String name, final int age, final Height height, final Double weight) {
        this.id = id;
        this.name = name;
        this.age = age;
        this.height = height;
        this.weight = weight == null ? 0 : weight;
    }

    private class Height {

    }
}

和 AnnotatedSubject 不同，在其构造方法上， height 参数的类型是 Height ，而不是 Integer 。因为 MyBatis 无法识别 Height 类，所以会创建 BadSubject 对象报错。

ExtensiveSubject

对应 extensive_subject 表，内容如下：

package org.apache.ibatis.autoconstructor;

public class ExtensiveSubject {
    private final byte aByte;
    private final short aShort;
    private final char aChar;
    private final int anInt;
    private final long aLong;
    private final float aFloat;
    private final double aDouble;
    private final boolean aBoolean;
    private final String aString;

    // enum types
    private final TestEnum anEnum;

    // array types

    // string to lob types:
    private final String aClob;
    private final String aBlob;

    public ExtensiveSubject(final byte aByte,
                            final short aShort,
                            final char aChar,
                            final int anInt,
                            final long aLong,
                            final float aFloat,
                            final double aDouble,
                            final boolean aBoolean,
                            final String aString,
                            final TestEnum anEnum,
                            final String aClob,
                            final String aBlob) {
        this.aByte = aByte;
        this.aShort = aShort;
        this.aChar = aChar;
        this.anInt = anInt;
        this.aLong = aLong;
        this.aFloat = aFloat;
        this.aDouble = aDouble;
        this.aBoolean = aBoolean;
        this.aString = aString;
        this.anEnum = anEnum;
        this.aClob = aClob;
        this.aBlob = aBlob;
    }

    public enum TestEnum {
        AVALUE, BVALUE, CVALUE;
    }
}

这是个复杂对象，基本涵盖了各种类型的数据。

AutoConstructorTest

单元测试类，内容如下：

package org.apache.ibatis.autoconstructor;

import org.apache.ibatis.BaseDataTest;
import org.apache.ibatis.exceptions.PersistenceException;
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.assertj.core.api.Assertions;
import org.junit.jupiter.api.BeforeAll;
import org.junit.jupiter.api.Test;

import java.io.Reader;
import java.util.List;

import static org.junit.jupiter.api.Assertions.assertNotNull;
import static org.junit.jupiter.api.Assertions.assertThrows;

class AutoConstructorTest {
  private static SqlSessionFactory sqlSessionFactory;

  @BeforeAll
  static void setUp() throws Exception {
    // 基于 mybatis-config.xml 配置文件创建 SqlSessionFactory 对象
    try (Reader reader = Resources.getResourceAsReader("org/apache/ibatis/autoconstructor/mybatis-config.xml")) {
      sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
    }

    // 基于 CreateDB.sql 初始化数据到内存数据库
    BaseDataTest.runScript(sqlSessionFactory.getConfiguration().getEnvironment().getDataSource(),
        "org/apache/ibatis/autoconstructor/CreateDB.sql");
  }

  @Test
  void fullyPopulatedSubject() {
    try (SqlSession sqlSession = sqlSessionFactory.openSession()) {
      final AutoConstructorMapper mapper = sqlSession.getMapper(AutoConstructorMapper.class);
      final Object subject = mapper.getSubject(1);
      assertNotNull(subject);
    }
  }

  @Test
  void primitiveSubjects() {
    try (SqlSession sqlSession = sqlSessionFactory.openSession()) {
      final AutoConstructorMapper mapper = sqlSession.getMapper(AutoConstructorMapper.class);
      assertThrows(PersistenceException.class, mapper::getSubjects);
    }
  }

  @Test
  void annotatedSubject() {
    try (SqlSession sqlSession = sqlSessionFactory.openSession()) {
      final AutoConstructorMapper mapper = sqlSession.getMapper(AutoConstructorMapper.class);
      verifySubjects(mapper.getAnnotatedSubjects());
    }
  }

  @Test
  void badSubject() {
    try (SqlSession sqlSession = sqlSessionFactory.openSession()) {
      final AutoConstructorMapper mapper = sqlSession.getMapper(AutoConstructorMapper.class);
      assertThrows(PersistenceException.class, mapper::getBadSubjects);
    }
  }

  @Test
  void extensiveSubject() {
    try (SqlSession sqlSession = sqlSessionFactory.openSession()) {
      final AutoConstructorMapper mapper = sqlSession.getMapper(AutoConstructorMapper.class);
      verifySubjects(mapper.getExtensiveSubject());
    }
  }

  private void verifySubjects(final List<?> subjects) {
    assertNotNull(subjects);
    Assertions.assertThat(subjects.size()).isEqualTo(3);
  }
}

执行任意一个测试方法，就可以开始调试了~~~