MyBatis(3)getMapper的实现

()

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

()

public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
    return (type, sqlSession);
}

()

public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
    //这是一个HashMap，取出注册的Mapper工厂
    final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>) (type);
    if (mapperProxyFactory == null) {
      throw new BindingException("Type " + type + " is not known to the MapperRegistry.");
    }
    try {
      //返回一个新的Mapper实现对象
      return (sqlSession);
    } catch (Exception e) {
      throw new BindingException("Error getting mapper instance. Cause: " + e, e);
    }
}

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

protected T newInstance(MapperProxy<T> mapperProxy) {
    //根据代理类，生成代理对象，实现Mapper接口
    return (T) ((), new Class[] { mapperInterface }, mapperProxy);
  }

.构造器

public class MapperProxy implements InvocationHandler, Serializable

public MapperProxy(SqlSession sqlSession, Class<T> mapperInterface, Map<Method, MapperMethod> methodCache) {
    this.sqlSession = sqlSession;
    this.mapperInterface = mapperInterface;
    this.methodCache = methodCache;
  }

  @Override
  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    try {
      //判断是不是toString()，hashCode()这种默认方法
      //这样的方法不需要处理
      if ((())) {
        return (this, args);
      } else if (isDefaultMethod(method)) {
        return invokeDefaultMethod(proxy, method, args);
      }
    } catch (Throwable t) {
      throw (t);
    }
    //去缓存中查找
    //有直接返回，没有则新建一个MapperMethod加入缓存并返回
    final MapperMethod mapperMethod = cachedMapperMethod(method);
    //对SqlSession的包装调用
    return (sqlSession, args);
  }

代理机制的核心类

public class MapperMethod {
  //封装了SQL标签，包括CRUD
  private final SqlCommand command;
  //封装了方法的参数信息和返回类型信息等
  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);
  }

  //对SqlSession的包装调用
  public Object execute(SqlSession sqlSession, Object[] args) {
    Object result;
    switch (()) {
      //如果是INSERT操作
      case INSERT: {
        //处理参数，将参数加进SQL的语句里面
        Object param = (args);
        //调用()获取结果
        result = rowCountResult(((), param));
        break;
      }
      case UPDATE: {
        Object param = (args);
        result = rowCountResult(((), param));
        break;
      }
      case DELETE: {
        Object param = (args);
        result = rowCountResult(((), param));
        break;
      }
      case SELECT:
        if (() && ()) {
          executeWithResultHandler(sqlSession, args);
          result = null;
        } else if (()) {
          result = executeForMany(sqlSession, args);
        } else if (()) {
          result = executeForMap(sqlSession, args);
        } else if (()) {
          result = executeForCursor(sqlSession, args);
        } else {
          Object param = (args);
          result = ((), param);
        }
        break;
      case FLUSH:
        result = ();
        break;
      default:
        throw new BindingException("Unknown execution method for: " + ());
    }
    if (result == null && ().isPrimitive() && !()) {
      throw new BindingException("Mapper method '" + () 
          + " attempted to return null from a method with a primitive return type (" + () + ").");
    }
    return result;
  }

private <E> Object executeForMany(SqlSession sqlSession, Object[] args) {
    List<E> result;
    Object param = (args);
    if (()) {
      RowBounds rowBounds = (args);
      result = sqlSession.<E>selectList((), param, rowBounds);
    } else {
      result = sqlSession.<E>selectList((), param);
    }
    // issue #510 Collections & arrays support
    if (!().isAssignableFrom(())) {
      if (().isArray()) {
        return convertToArray(result);
      } else {
        return convertToDeclaredCollection((), result);
      }
    }
    return result;
}

........

}

看到这里，我们会发现()就是绕一大圈去动态代理一个对象。这个对象根据返回类型和参数类型，最后用SqlSession的方法。

MapperMethod里面封装了自动根据配置，来使用SqlSession里面的方法。

和MethodSignature

  public static class SqlCommand {
    //XML标签的ID
    private final String name;
    //CRUD的标签<select><update>...
    private final SqlCommandType type;

    public SqlCommand(Configuration configuration, Class<?> mapperInterface, Method method) {
      final String methodName = ();
      final Class<?> declaringClass = ();
      //MappedStatement封装了一个配置文件(xml)的所有信息
      MappedStatement ms = resolveMappedStatement(mapperInterface, methodName, declaringClass,
          configuration);
      if (ms == null) {
        if (() != null) {
          name = null;
          type = ;
        } else {
          throw new BindingException("Invalid bound statement (not found): "
              + () + "." + methodName);
        }
      } else {
        name = ();
        type = ();
        if (type == ) {
          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 = () + "." + methodName;
      if ((statementId)) {
        return (statementId);
      } else if ((declaringClass)) {
        return null;
      }
      for (Class<?> superInterface : ()) {
        if ((superInterface)) {
          MappedStatement ms = resolveMappedStatement(superInterface, methodName,
              declaringClass, configuration);
          if (ms != null) {
            return ms;
          }
        }
      }
      return null;
    }
  }

  public static class MethodSignature {
    //是否返回多调结果
    private final boolean returnsMany;
    //返回Map
    private final boolean returnsMap;
    private final boolean returnsVoid;
    private final boolean returnsCursor;
    //自定义的返回类型
    private final Class<?> returnType;
    private final String mapKey;
    private final Integer resultHandlerIndex;
    private final Integer rowBoundsIndex;
    private final ParamNameResolver paramNameResolver;

看完上面的分析，就是通过一些方法的信息生成一个Mapper代理对象，并调用SqlSession的方法查询结果。

下次看看SqlSession的实现吧。