带码农《手写 Mybatis》进度 3：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);
}

@Testpublic 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
Process finished with exit code 0