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: