《Mybatis 手撸专栏》第11章：流程解耦，封装结果集处理器

mybatis-step-10
└── src
    ├── main
    │   └── java
    │       └── cn.bugstack.mybatis
    │           ├── binding
    │           ├── builder
    │           │   ├── xml
    │           │   │   ├── XMLConfigBuilder.java
    │           │   │   ├── XMLMapperBuilder.java
    │           │   │   └── XMLStatementBuilder.java
    │           │   ├── BaseBuilder.java
    │           │   ├── MapperBuilderAssistant.java
    │           │   ├── ParameterExpression.java
    │           │   ├── SqlSourceBuilder.java
    │           │   └── StaticSqlSource.java
    │           ├── datasource
    │           ├── executor
    │           │   ├── resultset
    │           │   │   └── ParameterHandler.java
    │           │   ├── resultset
    │           │   │   ├── DefaultResultContext.java
    │           │   │   └── DefaultResultHandler.java
    │           │   ├── resultset
    │           │   │   ├── DefaultResultSetHandler.java
    │           │   │   └── ResultSetHandler.java
    │           │   │   └── ResultSetWrapper.java
    │           │   ├── statement
    │           │   │   ├── BaseStatementHandler.java
    │           │   │   ├── PreparedStatementHandler.java
    │           │   │   ├── SimpleStatementHandler.java
    │           │   │   └── StatementHandler.java
    │           │   ├── BaseExecutor.java
    │           │   ├── Executor.java
    │           │   └── SimpleExecutor.java
    │           ├── io
    │           ├── mapping
    │           │   ├── BoundSql.java
    │           │   ├── Environment.java
    │           │   ├── MappedStatement.java
    │           │   ├── ParameterMapping.java
    │           │   ├── ResultMap.java
    │           │   ├── ResultMapping.java
    │           │   ├── SqlCommandType.java
    │           │   └── SqlSource.java
    │           ├── parsing
    │           ├── reflection
    │           ├── scripting
    │           ├── session
    │           │   ├── defaults
    │           │   │   ├── DefaultSqlSession.java
    │           │   │   └── DefaultSqlSessionFactory.java
    │           │   ├── Configuration.java
    │           │   ├── ResultContext.java
    │           │   ├── ResultHandler.java
    │           │   ├── RowBounds.java
    │           │   ├── SqlSession.java
    │           │   ├── SqlSessionFactory.java
    │           │   ├── SqlSessionFactoryBuilder.java
    │           │   └── TransactionIsolationLevel.java
    │           ├── transaction
    │           └── type
    │               ├── BaseTypeHandler.java
    │               ├── JdbcType.java
    │               ├── LongTypeHandler.java
    │               ├── StringTypeHandler.java
    │               ├── TypeAliasRegistry.java
    │               ├── TypeHandler.java
    │               └── TypeHandlerRegistry.java
    └── test
        ├── java
        │   └── cn.bugstack.mybatis.test.dao
        │       ├── dao
        │       │   └── IUserDao.java
        │       ├── po
        │       │   └── User.java
        │       └── ApiTest.java
        └── resources
            ├── mapper
            │   └──User_Mapper.xml
            └── mybatis-config-datasource.xml

public class ResultMap {

    private String id;
    private Class<?> type;
    private List<ResultMapping> resultMappings;
    private Set<String> mappedColumns;

  //...
}

public class MapperBuilderAssistant extends BaseBuilder {

    /**
     * 添加映射器语句
     */
    public MappedStatement addMappedStatement(
            String id,
            SqlSource sqlSource,
            SqlCommandType sqlCommandType,
            Class<?> parameterType,
            String resultMap,
            Class<?> resultType,
            LanguageDriver lang
    ) {
        // 给id加上namespace前缀：cn.bugstack.mybatis.test.dao.IUserDao.queryUserInfoById
        id = applyCurrentNamespace(id, false);
        MappedStatement.Builder statementBuilder = new MappedStatement.Builder(configuration, id, sqlCommandType, sqlSource, resultType);

        // 结果映射，给 MappedStatement#resultMaps
        setStatementResultMap(resultMap, resultType, statementBuilder);

        MappedStatement statement = statementBuilder.build();
        // 映射语句信息，建造完存放到配置项中
        configuration.addMappedStatement(statement);

        return statement;
    }

    private void setStatementResultMap(
            String resultMap,
            Class<?> resultType,
            MappedStatement.Builder statementBuilder) {
        List<ResultMap> resultMaps = new ArrayList<>();
        /*
         * 通常使用 resultType 即可满足大部分场景
         * <select id="queryUserInfoById" resultType="cn.bugstack.mybatis.test.po.User">
         * 使用 resultType 的情况下，Mybatis 会自动创建一个 ResultMap，基于属性名称映射列到 JavaBean 的属性上。
         */
        ResultMap.Builder inlineResultMapBuilder = new ResultMap.Builder(
                configuration,
                statementBuilder.id() + "-Inline",
                resultType,
                new ArrayList<>());
        resultMaps.add(inlineResultMapBuilder.build());
        statementBuilder.resultMaps(resultMaps);
    }

}

public class DefaultResultHandler implements ResultHandler {

    private final List<Object> list;
    /**
     * 通过 ObjectFactory 反射工具类，产生特定的 List
     */
    @SuppressWarnings("unchecked")
    public DefaultResultHandler(ObjectFactory objectFactory) {
        this.list = objectFactory.create(List.class);
    }

    @Override
    public void handleResult(ResultContext context) {
        list.add(context.getResultObject());
    }

}

private Object createResultObject(ResultSetWrapper rsw, ResultMap resultMap, List<Class<?>> constructorArgTypes, List<Object> constructorArgs, String columnPrefix) throws SQLException {
    final Class<?> resultType = resultMap.getType();
    final MetaClass metaType = MetaClass.forClass(resultType);
    if (resultType.isInterface() || metaType.hasDefaultConstructor()) {
        // 普通的Bean对象类型
        return objectFactory.create(resultType);
    }
    throw new RuntimeException("Do not know how to create an instance of " + resultType);
}

CREATE TABLE
    USER
    (
        id bigint NOT NULL AUTO_INCREMENT COMMENT '自增ID',
        userId VARCHAR(9) COMMENT '用户ID',
        userHead VARCHAR(16) COMMENT '用户头像',
        createTime TIMESTAMP NULL COMMENT '创建时间',
        updateTime TIMESTAMP NULL COMMENT '更新时间',
        userName VARCHAR(64),
        PRIMARY KEY (id)
    )
    ENGINE=InnoDB DEFAULT CHARSET=utf8;
    
insert into user (id, userId, userHead, createTime, updateTime, userName) values (1, '10001', '1_04', '2022-04-13 00:00:00', '2022-04-13 00:00:00', '小傅哥');    

<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://127.0.0.1:3306/mybatis?useUnicode=true"/>
            <property name="username" value="root"/>
            <property name="password" value="123456"/>
        </dataSource>
    </environment>
</environments>

<select id="queryUserInfoById" parameterType="java.lang.Long" resultType="cn.bugstack.mybatis.test.po.User">
    SELECT id, userId, userName, userHead
    FROM user
    where id = #{id}
</select>

@Before
public void init() throws IOException {
    // 1. 从SqlSessionFactory中获取SqlSession
    SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(Resources.getResourceAsReader("mybatis-config-datasource.xml"));
    sqlSession = sqlSessionFactory.openSession();
}

@Test
public void test_queryUserInfoById() {
    // 1. 获取映射器对象
    IUserDao userDao = sqlSession.getMapper(IUserDao.class);
    // 2. 测试验证：基本参数
    User user = userDao.queryUserInfoById(1L);
    logger.info("测试结果：{}", JSON.toJSONString(user));
}

12:39:17.321 [main] INFO  c.b.mybatis.builder.SqlSourceBuilder - 构建参数映射 property：id propertyType：class java.lang.Long
12:39:17.321 [main] INFO  c.b.mybatis.builder.SqlSourceBuilder - 构建参数映射 property：userId propertyType：class java.lang.String
12:39:17.382 [main] INFO  c.b.m.s.defaults.DefaultSqlSession - 执行查询 statement：cn.bugstack.mybatis.test.dao.IUserDao.queryUserInfoById parameter：1
12:39:17.684 [main] INFO  c.b.m.s.d.DefaultParameterHandler - 根据每个ParameterMapping中的TypeHandler设置对应的参数信息 value：1
12:39:17.728 [main] INFO  cn.bugstack.mybatis.test.ApiTest - 测试结果：{"id":1,"userHead":"1_04","userId":"10001","userName":"小傅哥"}

Process finished with exit code 0