Floodlight 中创建消息对象的方法

  

     在 floodlight 中创建各种openflow message 和 action 等採用的是简单工厂方式。BasicFactory类（实现OFMessageFactory接口。）会依据消息的类型创建不同的对象，达到更好的封装效果。此外这里调用的是枚举类型的方法。以下是详细代码：

----------工厂接口，还有OFActionFactory。约束须要详细工厂完毕的事情

public interface OFMessageFactory
{

      // 依据消息类型得到详细的实例

      public OFMessage
getMessage(OFType t);

      // 尝试从ChannelBuffer中解析出尽可能多的OFMessage，从position開始，止于一个解析的消息之后

      public List <OFMessage>
parseMessage(ChannelBuffer data)

               throws MessageParseException;

      // 得到负责创建openflow action
的工厂

      public OFActionFactory
getActionFactory();

}

---------工厂类

   //创建 openflow message和action

public class BasicFactory implements OFMessageFactory,
OFActionFactory,

          OFStatisticsFactory, OFVendorDataFactory {

      @Override

      public OFMessage
getMessage(OFType t) {

           return t.newInstance(); //
调用枚举类型的方法

     }

      @Override

      public List<OFMessage>
parseMessage(ChannelBuffer data)

               throws MessageParseException
{

          List<OFMessage> msglist = new ArrayList<OFMessage>();

          OFMessage msg = null ;

           while (data.readableBytes()
>= OFMessage.MINIMUM_LENGTH ) {

              data.markReaderIndex(); //
标记读指针，注意ChannelBuffer和ByteBuffer的差别

              msg = this .parseMessageOne(data);

               if (msg
== null ) {

                   data.resetReaderIndex(); //
假设失败则恢复read index

                    break ;

              } else {

                   msglist.add(msg); //
成功解析。则将其增加列表

              }

          }

           if (msglist.size()
== 0) {

               return null ;

          }

           return msglist;

     }

      public OFMessage
parseMessageOne(ChannelBuffer data)

               throws MessageParseException
{

           try {

              OFMessage demux = new OFMessage();

              OFMessage ofm = null ;

               if (data.readableBytes()
< OFMessage.MINIMUM_LENGTH )

                    return ofm;

              data.markReaderIndex();

               //
调用基类方法，得到OF header的字段如长度和消息类型

              demux.readFrom(data);

              data.resetReaderIndex();

               //
假设ChannelBuffer中不足一个消息长度，则返回空

               if (demux.getLengthU()
> data.readableBytes())

                    return ofm;

               //
否则依据类型。创建对应的消息对象

              ofm = getMessage(demux.getType());

               if (ofm
== null )

                    return null ;

               //
假设对应的消息类中有OFActionFactory成员，就用当前类设置它

               if (ofm instanceof OFActionFactoryAware)
{

                   ((OFActionFactoryAware) ofm).setActionFactory(this );

              }

               if (ofm instanceof OFMessageFactoryAware)
{

                   ((OFMessageFactoryAware) ofm).setMessageFactory(this );

              }

               if (ofm instanceof OFStatisticsFactoryAware)
{

                   ((OFStatisticsFactoryAware) ofm).setStatisticsFactory(this );

              }

               if (ofm instanceof OFVendorDataFactoryAware)
{

                   ((OFVendorDataFactoryAware) ofm).setVendorDataFactory(this );

              }

               //
最后调用详细类的readFrom。从ChannelBuffer解析出该消息

              ofm.readFrom(data);

               if (OFMessage. class.equals(ofm.getClass()))
{

                    //
advance the position for un-implemented messages

                   data.readerIndex(data.readerIndex()

                             + (ofm.getLengthU() - OFMessage.MINIMUM_LENGTH ));

              }

               return ofm;

          } catch (Exception
e) {

               throw new MessageParseException(e);

          }

     }

// 以下的action和statistics 与上面类似。 

         @Override

      public OFAction
getAction(OFActionType t) {

           return t.newInstance();

     }

      @Override

      public List<OFAction>
parseActions(ChannelBuffer data, int length)
{

           return parseActions(data,
length, 0);

     }

      @Override

      public List<OFAction>
parseActions(ChannelBuffer data, int length, int limit)
{

          List<OFAction> results = new ArrayList<OFAction>();

          OFAction demux = new OFAction();

          OFAction ofa;

           int end
= data.readerIndex() + length;

           while (limit
== 0 || results.size() <= limit) {

               if ((data.readableBytes()
< OFAction.MINIMUM_LENGTH || (data

                        .readerIndex() + OFAction.MINIMUM_LENGTH )
> end))

                    return results;

              data.markReaderIndex();

              demux.readFrom(data);

              data.resetReaderIndex();

               if ((demux.getLengthU()
> data.readableBytes() || (data

                        .readerIndex() + demux.getLengthU()) > end))

                    return results;

              ofa = getAction(demux.getType());

              ofa.readFrom(data);

               if (OFAction. class.equals(ofa.getClass()))
{

                    //
advance the position for un-implemented messages

                   data.readerIndex(data.readerIndex()

                             + (ofa.getLengthU() - OFAction.MINIMUM_LENGTH ));

              }

              results.add(ofa);

          }

           return results;

     }

      

      @Override

      public OFActionFactory
getActionFactory() {

           return this ;

     }

}