使用set出现问题，size有时变为0

[机器学习之禅]

在for循环中显示set的size，没有问题，随着数据增加size也增加，
但是后面那条size就变为0了，这是为什么？
关键是还不是所有数据都这样

while ((s1 = br.readLine()) != null)
		{
			Set<String> usrSet = new HashSet<String>();
			try
			{
			LOG.info("[INFO] The "+count+" ID.");
			count++;
			
				// 获取一个用户id
				String id = s1;
				// 根据id获取用户行为记录
				HashMap<String, String> usrlog_hashmap = new HashMap<String, String>();
				usrlog_hashmap = logDBOperation.queryUserIDInDateRange(id, timeStamp, 7);//logDBOperation.queryByUsrID(id);//queryUserIDInDateRange(id, "2014061900000", 500);//;queryUserIDInDateRange
				int tempcount = 0;
				// 循环读取用户行为
				for (Entry<String, String> entry : usrlog_hashmap.entrySet())
				{
					//System.out.println(entry.getValue() + "\n");
					String[] usrlog = entry.getValue().split("!");
					for(String tem : usrlog)
					{
						//System.out.println(tem + "\n");
						tempcount++;
						countUserLog++;
						//匹配
						Matcher matcher = pattern.matcher(tem);
						if(matcher.find())
						{
							//System.out.println(tem + "\n");
							countUsefulLog++;
							String postid = matcher.group(1);
							String leftStr = matcher.group(2);
							//System.out.println("postid "+postid);
							Item item = null;
							boolean flag = true;
							while(flag)
							{
								try
								{
									item = itemop.get(postid);
		
									flag = false;
								}
								catch(Exception e)
								{
									LOG.error("[ERROR] Get item failed.");
									continue;
								}
							}
							
							String channel = "";
							
								
							try{
								channel = channelsParser.getInstance(ItemOperation.ItemType.APPITEM).getTransChannelByItem(item,0);
	
							}	
							catch(java.lang.NoClassDefFoundError e)
							{
								LOG.error("[ERROR] Get channel failed.");
								continue;
							}
							if(channel == null || channel == "" || channel == " ")
							{
								Matcher matcher1 = pattern1.matcher(leftStr);
								if(matcher1.find())
								{
										channel = matcher1.group(1);
										System.out.println("channel: "+channel);	
										countref++;
								}
							}
								//System.out.println("channel: "+channel);	
							String[] row = channel.split("-");
							for(int i = 1; i < row.length; i++)
							{
								row[i] = row[i-1]+"-"+row[i];
							}
							
							for(int j = 0; j < row.length; j++)
							{
								System.out.println("row[j] "+ row[j]);
								usrSet.add(row[j]);
								System.out.println("usrSet.size() "+usrSet.size());
							}
							//String[] channelclass = channel.split("/");
						}
					}
					
				}
				System.out.println("usrSet.size() "+usrSet.size());
				
			}
				catch(Exception e)
				{
					LOG.error("Something wrong with me.");
					continue;
				}
		}