java多線程均攤任務

多線程均攤任務

學習記錄

代碼如下:

 public static void main(String[] args) {
        Date startDate = new Date();
        try {
            //創建一個任務提供給線程
            List<String> list = new ArrayList<>();
            for (int i = 0; i < 100; i++) {
                list.add(i + ",");
            }
            //創建5個線程並啓動,可更改成任意數量線程
            System.out.println(new Test().list2Str(list, 5));
        } catch (Exception e) {
            e.printStackTrace();
        }finally {
            System.out.println("=====================耗時" + (new Date().getTime() - startDate.getTime()) / 1000 + "s");
        }
    }

    public String list2Str(final List<String> list, final int nThreads) throws Exception {
        if (list == null || list.isEmpty()) {
            return null;
        }
        int len = 0;
        for (String str : list) {
            len += str.length();
        }
        StringBuffer ret = new StringBuffer(len);

        final int size = list.size();
        ExecutorService executorService = Executors.newFixedThreadPool(nThreads);
        List<Future<String>> futures = new ArrayList<Future<String>>(nThreads);
        try {
            for (int i = 0; i < nThreads; i++) {
                int d = i;
                final int j = i;
                Callable<String> task = new Callable<String>() {
                    @Override
                    public String call() throws Exception {
                        int len = 0;
                        //讀取數據總長度防止內存溢出
                        for (int n = size / nThreads * j; n < size / nThreads * (j + 1); n++) {
                            len += list.get(n).length();
                        }
                        //把數據按算法平均分給線程
                        StringBuffer sb = new StringBuffer(len);
                        for (int n = size / nThreads * j; n < size / nThreads * (j + 1); n++) {
                            sb.append(list.get(n));
                            System.out.println("第"+d+"個線程:"+list.get(n));
                        }
                        return sb.toString();
                    }
                };
                futures.add(executorService.submit(task));
            }

            for (Future<String> future : futures) {
                ret.append(future.get());
            }
        } finally {
            executorService.shutdown();
        }

        return ret.toString();
    }

結果如下: