多线程代码

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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();  
        }  
    }