MyBatis (3) getMapper () 의 실현

1.SqlSession.getMapper()

public  T getMapper(Class type) {
    return configuration.getMapper(type, this);
}

2.Configuration.getMapper()

public  T getMapper(Class type, SqlSession sqlSession) {
    return mapperRegistry.getMapper(type, sqlSession);
}

3.MapperRegistry.getMapper()

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

4.MapperProxyFactory.newInstance

public T newInstance(SqlSession sqlSession) {
    //  Mapper   
    final MapperProxy mapperProxy = new MapperProxy(sqlSession, mapperInterface, methodCache);
    return newInstance(mapperProxy);
}

protected T newInstance(MapperProxy mapperProxy) {
    //     ，      ，  Mapper  
    return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy);
  }

5. MapperProxy. 구조 기
public class MapperProxy implements InvocationHandler, Serializable

public MapperProxy(SqlSession sqlSession, Class mapperInterface, Map methodCache) {
    this.sqlSession = sqlSession;
    this.mapperInterface = mapperInterface;
    this.methodCache = methodCache;
  }

  @Override
  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    try {
      //     toString()，hashCode()      
      //          
      if (Object.class.equals(method.getDeclaringClass())) {
        return method.invoke(this, args);
      } else if (isDefaultMethod(method)) {
        return invokeDefaultMethod(proxy, method, args);
      }
    } catch (Throwable t) {
      throw ExceptionUtil.unwrapThrowable(t);
    }
    //      
    //     ，       MapperMethod       
    final MapperMethod mapperMethod = cachedMapperMethod(method);
    // SqlSession     
    return mapperMethod.execute(sqlSession, args);
  }

5. MapperMethod 에이전트 의 핵심 클래스

public class MapperMethod {
  //   SQL  ，  CRUD
  private final SqlCommand command;
  //                  
  private final MethodSignature method;

  public MapperMethod(Class> mapperInterface, Method method, Configuration config) {
    this.command = new SqlCommand(config, mapperInterface, method);
    this.method = new MethodSignature(config, mapperInterface, method);
  }

  // SqlSession     
  public Object execute(SqlSession sqlSession, Object[] args) {
    Object result;
    switch (command.getType()) {
      //   INSERT  
      case INSERT: {
        //    ，     SQL     
        Object param = method.convertArgsToSqlCommandParam(args);
        //  SqlSession.insert()    
        result = rowCountResult(sqlSession.insert(command.getName(), param));
        break;
      }
      case UPDATE: {
        Object param = method.convertArgsToSqlCommandParam(args);
        result = rowCountResult(sqlSession.update(command.getName(), param));
        break;
      }
      case DELETE: {
        Object param = method.convertArgsToSqlCommandParam(args);
        result = rowCountResult(sqlSession.delete(command.getName(), param));
        break;
      }
      case SELECT:
        if (method.returnsVoid() && method.hasResultHandler()) {
          executeWithResultHandler(sqlSession, args);
          result = null;
        } else if (method.returnsMany()) {
          result = executeForMany(sqlSession, args);
        } else if (method.returnsMap()) {
          result = executeForMap(sqlSession, args);
        } else if (method.returnsCursor()) {
          result = executeForCursor(sqlSession, args);
        } else {
          Object param = method.convertArgsToSqlCommandParam(args);
          result = sqlSession.selectOne(command.getName(), param);
        }
        break;
      case FLUSH:
        result = sqlSession.flushStatements();
        break;
      default:
        throw new BindingException("Unknown execution method for: " + command.getName());
    }
    if (result == null && method.getReturnType().isPrimitive() && !method.returnsVoid()) {
      throw new BindingException("Mapper method '" + command.getName() 
          + " attempted to return null from a method with a primitive return type (" + method.getReturnType() + ").");
    }
    return result;
  }

private  Object executeForMany(SqlSession sqlSession, Object[] args) {
    List result;
    Object param = method.convertArgsToSqlCommandParam(args);
    if (method.hasRowBounds()) {
      RowBounds rowBounds = method.extractRowBounds(args);
      result = sqlSession.selectList(command.getName(), param, rowBounds);
    } else {
      result = sqlSession.selectList(command.getName(), param);
    }
    // issue #510 Collections & arrays support
    if (!method.getReturnType().isAssignableFrom(result.getClass())) {
      if (method.getReturnType().isArray()) {
        return convertToArray(result);
      } else {
        return convertToDeclaredCollection(sqlSession.getConfiguration(), result);
      }
    }
    return result;
}

........

}

여기 서 보면 SqlSession. getMapper () 는 한 바퀴 크게 돌아 서 동적 대리 대상 을 찾 는 것 을 발견 할 수 있 습 니 다.이 대상 은 반환 형식 과 매개 변수 유형 에 따라 마지막 으로 SqlSession 방법 을 사용 합 니 다.
MapperMethod 에는 설정 에 따라 SqlSession 의 방법 을 사용 하 는 자동 패키지 가 들 어 있 습 니 다.
6. SqlCommand 와 MethodSignature

  public static class SqlCommand {
    //XML   ID
    private final String name;
    //CRUD   ...
    private final SqlCommandType type;

    public SqlCommand(Configuration configuration, Class> mapperInterface, Method method) {
      final String methodName = method.getName();
      final Class> declaringClass = method.getDeclaringClass();
      //MappedStatement         (xml)     
      MappedStatement ms = resolveMappedStatement(mapperInterface, methodName, declaringClass,
          configuration);
      if (ms == null) {
        if (method.getAnnotation(Flush.class) != null) {
          name = null;
          type = SqlCommandType.FLUSH;
        } else {
          throw new BindingException("Invalid bound statement (not found): "
              + mapperInterface.getName() + "." + methodName);
        }
      } else {
        name = ms.getId();
        type = ms.getSqlCommandType();
        if (type == SqlCommandType.UNKNOWN) {
          throw new BindingException("Unknown execution method for: " + name);
        }
      }
    }

    public String getName() {
      return name;
    }

    public SqlCommandType getType() {
      return type;
    }

    private MappedStatement resolveMappedStatement(Class> mapperInterface, String methodName,
        Class> declaringClass, Configuration configuration) {
      String statementId = mapperInterface.getName() + "." + methodName;
      if (configuration.hasStatement(statementId)) {
        return configuration.getMappedStatement(statementId);
      } else if (mapperInterface.equals(declaringClass)) {
        return null;
      }
      for (Class> superInterface : mapperInterface.getInterfaces()) {
        if (declaringClass.isAssignableFrom(superInterface)) {
          MappedStatement ms = resolveMappedStatement(superInterface, methodName,
              declaringClass, configuration);
          if (ms != null) {
            return ms;
          }
        }
      }
      return null;
    }
  }

  public static class MethodSignature {
    //        
    private final boolean returnsMany;
    //  Map
    private final boolean returnsMap;
    private final boolean returnsVoid;
    private final boolean returnsCursor;
    //        
    private final Class> returnType;
    private final String mapKey;
    private final Integer resultHandlerIndex;
    private final Integer rowBoundsIndex;
    private final ParamNameResolver paramNameResolver;

위의 분석 을 보면 일부 방법의 정 보 를 통 해 Mapper 대리 대상 을 만 들 고 SqlSession 방법 으로 결 과 를 조회 하 는 것 이다.
다음 에 SqlSession 의 실현 을 봅 시다.