java8 parallel并行处理（附对比）

适用场景：前提保证线程安全，例如需要将多个文件下载保存到服务器

通常写法：

public static void main(String[] args) {
    List list = new ArrayList<>();
    list.add("http://172.16.140.152:8080/cms1/filePath/Image/2019-08-26/4e0ee00927534036af9a9aae1a545af7-1_201908261600517471.bmp");
    list.add("http://172.16.140.152:8080/cms1/filePath/Image/2019-08-26/4e0ee00927534036af9a9aae1a545af7-2.bmp");
    list.add("http://172.16.140.152:8080/cms1/filePath/Image/2019-08-26/d6f0f7d8b5064e47b62f1e13014b92be.jpg");
    list.add("http://172.16.140.152:8080/cms1/filePath/Image/2019-08-26/85da58f7095043cc815bcb1840544a01-1.bmp");
    list.add("http://172.16.140.152:8080/cms1/filePath/Image/2019-08-26/85da58f7095043cc815bcb1840544a01-1_2.bmp");
    list.add("http://172.16.140.152:8080/cms1/filePath/Image/2019-08-26/94264b3d3e8f4d1bad87397138d07e66.jpg");
    list.add("http://172.16.140.152:8080/cms1/filePath/Image/2019-08-26/dd7d4342d01f479a85c5951ac034b286.bmp");
    long start = System.currentTimeMillis();
    for (String s : list) {
      UrlFileUtil.downloadFile(s,"/Users/jianglinmao/Downloads/img");
    }
    long end = System.currentTimeMillis();
    System.out.println("运行时间：" + (end - start));
  }

运行时间：541毫秒

java8 parallel 处理方法：

public static void main(String[] args) {
    List list = new ArrayList<>();
    list.add("http://172.16.140.152:8080/cms1/filePath/Image/2019-08-26/4e0ee00927534036af9a9aae1a545af7-1_201908261600517471.bmp");
    list.add("http://172.16.140.152:8080/cms1/filePath/Image/2019-08-26/4e0ee00927534036af9a9aae1a545af7-2.bmp");
    list.add("http://172.16.140.152:8080/cms1/filePath/Image/2019-08-26/d6f0f7d8b5064e47b62f1e13014b92be.jpg");
    list.add("http://172.16.140.152:8080/cms1/filePath/Image/2019-08-26/85da58f7095043cc815bcb1840544a01-1.bmp");
    list.add("http://172.16.140.152:8080/cms1/filePath/Image/2019-08-26/85da58f7095043cc815bcb1840544a01-1_2.bmp");
    list.add("http://172.16.140.152:8080/cms1/filePath/Image/2019-08-26/94264b3d3e8f4d1bad87397138d07e66.jpg");
    list.add("http://172.16.140.152:8080/cms1/filePath/Image/2019-08-26/dd7d4342d01f479a85c5951ac034b286.bmp");
    long start = System.currentTimeMillis();
    list.stream().parallel().forEach(s -> {
      UrlFileUtil.downloadFile(s,"/Users/jianglinmao/Downloads/img");
    });
    long end = System.currentTimeMillis();
    System.out.println("运行时间：" + (end - start));
  }

运行时间：276毫秒

很明显，通过parallel进行并行处理，效率大概提高了将近一倍！