Storm学习00--IComponent

##IComponent
IComponent继承Serializable接口， 为topology中所有可能组件提供共同的方法。

 interface IComponent extends Serializable

提供两个方法

/**
 * Common methods for all possible components in a topology. This interface is used
 * when defining topologies using the Java API. 
 */
public interface IComponent extends Serializable {

    /**
     * Declare the output schema for all the streams of this topology.
     *
     * @param declarer this is used to declare output stream ids, output fields, and whether or not each output stream is a direct stream
     */
    void declareOutputFields(OutputFieldsDeclarer declarer);

    /**
     * Declare configuration specific to this component. Only a subset of the "topology.*" configs can
     * be overridden. The component configuration can be further overridden when constructing the 
     * topology using {@link TopologyBuilder}
     *
     */
    Map<String, Object> getComponentConfiguration();

}

1.1 declareOutputFields(OutputFieldsDeclarer declarer)

  此方法用于声明当前Spout的Tuple发送流。Stream流的定义是通过OutputFieldsDeclarer.declare方法完成的，其中的参数包括了发送的域Fields。
如： 在RandomSentenceSpout中重写了

  @Override
  public void declareOutputFields(OutputFieldsDeclarer declarer) {
    declarer.declare(new Fields("word"));}  

1.2 getComponentConfiguration();

 &mesp;此方法用于声明针对当前组件的特殊的Configuration配置。