Guava FluentIterable - 模拟 JAVA 8 Stream in JAVA 7

 
    // First we assume all old entries needs to be deleted and then we figure out the ones to keep
    Map toDeleteEntries = FluentIterable.from( knownEntries )
        .uniqueIndex( new Function()
          {
            @Override
            public String apply( StreamEntry entry )
            {
              CalendarStreamRawData rawCalendar = (CalendarStreamRawData) entry.getRawdata();
              return rawCalendar.getItemSourceType() + "::" + rawCalendar.getItemSourceId().toString();
            }
          } );

    .................................

    // Fill toDelete list,  basically all items that are not in toKeep list will be deleted
    Collection toDelete = FluentIterable.from( toDeleteEntries.values() )
        .transform( new Function()
          {
            @Override
            public Long apply( StreamEntry entry )
            {
              return entry.getSequenceID();
            }
          } ).toList();