《Mybatis 手撸专栏》第3章：实现映射器的注册和使用

mybatis-step-02
└── src
    ├── main
    │   └── java
    │       └── cn.bugstack.mybatis
    │           ├── binding
    │           │   ├── MapperProxy.java
    │           │   ├── MapperProxyFactory.java
    │           │   └── MapperRegistry.java
    │           └── session
    │               ├── defaults
    │               │   ├── DefaultSqlSession.java
    │               │   └── DefaultSqlSessionFactory.java
    │               ├── SqlSession.java
    │               └── SqlSessionFactory.java
    └── test
        └── java
            └── cn.bugstack.mybatis.test.dao
                ├── dao
                │   ├── ISchoolDao.java
                │   └── IUserDao.java
                └── ApiTest.java

public class MapperRegistry {

    /**
     * 将已添加的映射器代理加入到 HashMap
     */
    private final Map<Class<?>, MapperProxyFactory<?>> knownMappers = new HashMap<>();

    public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
        final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>) knownMappers.get(type);
        if (mapperProxyFactory == null) {
            throw new RuntimeException("Type " + type + " is not known to the MapperRegistry.");
        }
        try {
            return mapperProxyFactory.newInstance(sqlSession);
        } catch (Exception e) {
            throw new RuntimeException("Error getting mapper instance. Cause: " + e, e);
        }
    }

    public <T> void addMapper(Class<T> type) {
        /* Mapper 必须是接口才会注册 */
        if (type.isInterface()) {
            if (hasMapper(type)) {
                // 如果重复添加了，报错
                throw new RuntimeException("Type " + type + " is already known to the MapperRegistry.");
            }
            // 注册映射器代理工厂
            knownMappers.put(type, new MapperProxyFactory<>(type));
        }
    }

    public void addMappers(String packageName) {
        Set<Class<?>> mapperSet = ClassScanner.scanPackage(packageName);
        for (Class<?> mapperClass : mapperSet) {
            addMapper(mapperClass);
        }
    }

}

public interface SqlSession {

    /**
     * Retrieve a single row mapped from the statement key
     * 根据指定的SqlID获取一条记录的封装对象
     *
     * @param <T>       the returned object type 封装之后的对象类型
     * @param statement sqlID
     * @return Mapped object 封装之后的对象
     */
    <T> T selectOne(String statement);

    /**
     * Retrieve a single row mapped from the statement key and parameter.
     * 根据指定的SqlID获取一条记录的封装对象，只不过这个方法容许我们可以给sql传递一些参数
     * 一般在实际使用中，这个参数传递的是pojo，或者Map或者ImmutableMap
     *
     * @param <T>       the returned object type
     * @param statement Unique identifier matching the statement to use.
     * @param parameter A parameter object to pass to the statement.
     * @return Mapped object
     */
    <T> T selectOne(String statement, Object parameter);

    /**
     * Retrieves a mapper.
     * 得到映射器，这个巧妙的使用了泛型，使得类型安全
     *
     * @param <T>  the mapper type
     * @param type Mapper interface class
     * @return a mapper bound to this SqlSession
     */
    <T> T getMapper(Class<T> type);

}

public class DefaultSqlSession implements SqlSession {

    /**
     * 映射器注册机
     */
    private MapperRegistry mapperRegistry;

    @Override
    public <T> T selectOne(String statement, Object parameter) {
        return (T) ("你被代理了！" + "方法：" + statement + " 入参：" + parameter);
    }

    @Override
    public <T> T getMapper(Class<T> type) {
        return mapperRegistry.getMapper(type, this);
    }

}

public interface SqlSessionFactory {

    /**
     * 打开一个 session
     * @return SqlSession
     */
   SqlSession openSession();

}

public class DefaultSqlSessionFactory implements SqlSessionFactory {

    private final MapperRegistry mapperRegistry;

    public DefaultSqlSessionFactory(MapperRegistry mapperRegistry) {
        this.mapperRegistry = mapperRegistry;
    }

    @Override
    public SqlSession openSession() {
        return new DefaultSqlSession(mapperRegistry);
    }

}

public interface ISchoolDao {

    String querySchoolName(String uId);

}

public interface IUserDao {

    String queryUserName(String uId);

    Integer queryUserAge(String uId);

}

@Test
public void test_MapperProxyFactory() {
    // 1. 注册 Mapper
    MapperRegistry registry = new MapperRegistry();
    registry.addMappers("cn.bugstack.mybatis.test.dao");
    
    // 2. 从 SqlSession 工厂获取 Session
    SqlSessionFactory sqlSessionFactory = new DefaultSqlSessionFactory(registry);
    SqlSession sqlSession = sqlSessionFactory.openSession();
    
    // 3. 获取映射器对象
    IUserDao userDao = sqlSession.getMapper(IUserDao.class);
    
    // 4. 测试验证
    String res = userDao.queryUserName("10001");
    logger.info("测试结果：{}", res);
}

22:43:23.254 [main] INFO  cn.bugstack.mybatis.test.ApiTest - 测试结果：你被代理了！方法：queryUserName 入参：[Ljava.lang.Object;@50cbc42f

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