多并發(fā)下多線程遍歷list問題

今天做導(dǎo)出 查出的數(shù)據(jù)有3萬條 還要遍歷做一些處理 結(jié)果就超時
想到多線程遍歷list 去網(wǎng)上查找 找到這塊代碼：

public String list2Str(List<String> list, final int nThreads) throws Exception {  
            if (list == null || list.isEmpty()) {  
                return null;  
            }  
              
            StringBuffer ret = new StringBuffer();  
      
            int size = list.size();  
            ExecutorService executorService = Executors.newFixedThreadPool(nThreads);  
            List<Future<String>> futures = new ArrayList<Future<String>>(nThreads);  
              
            for (int i = 0; i < nThreads; i++) {  
                final List<String> subList = list.subList(size / nThreads * i, size / nThreads * (i + 1));  
                Callable<String> task = new Callable<String>() {  
                    @Override  
                    public String call() throws Exception {  
                        StringBuffer sb = new StringBuffer();  
                        for (String str : subList) {  
                            sb.append(str);  
                        }  
                        return sb.toString();  
                    }  
                };  
                futures.add(executorService.submit(task));  
            }  
              
            for (Future<String> future : futures) {  
                ret.append(future.get());  
            }  
            executorService.shutdown();  
              
            return ret.toString();  
        }  
    } 

我調(diào)用時開了5個線程 我想問 每次導(dǎo)出就開啟5個線程 如果多個人同時導(dǎo)出 比如10000個人同時導(dǎo)出 那豈不是就開啟了50000個線程了！??！

沒問題嗎？？？