Flink 常见 Iterable 转 List，List treeMap的使用

妖狐艹你老母 2024-04-17 16:24 56阅读 0赞

> 1，Iterable转List
> 
>     Iterable<Entity> geted = entityDao.findAll();
>     List<Entity> list = Lists.newArrays();
>     geted.forEach(single ->{list.add(single)});
> 
> 学习了：https://blog.csdn.net/u010003051/article/details/53422741
> 
>  
> 
> Iterator转List
> 
>     方式1：
>     #Apache Commons Collections:
>     import org.apache.commons.collections.IteratorUtils;
>     Iterator<Element> myIterator = //some iterator
>     List<Element> myList=IteratorUtils.toList(myIterator);   
>      
>      
>     方式二：
>     或者自己转换
>     public static <T> List<T> copyIterator(Iterator<T> iter) {
>         List<T> copy = new ArrayList<T>();
>         while (iter.hasNext())
>             copy.add(iter.next());
>         return copy;
>     }
>      
>     使用方式：
>     List<String> list = Arrays.asList("1", "2", "3");
>     Iterator<String> iter = list.iterator();
>     List<String> copy = copyIterator(iter);

2，List 跟 treeMap 在topN中的使用

>     List<Tuple2<String, Integer>>  list = new ArrayList<>();
>     System.out.println("list = " + list);
>     input.forEach(single ->{
>         list.add(single);
>     });
>     Collections.sort(list,new Comparator<Tuple2<String, Integer>>() {
>     
>         @Override
>         public int compare(Tuple2<String, Integer> o1, Tuple2<String, Integer> o2) {
>     
>             int i = o1.f1 - o2.f1;
>             return i;
>         }
>     });
>     System.out.println("list = " + list);
>     List<Tuple2<String, Integer>> tuple2s = list.subList(0, 2);
>     
>     //treemap按照key降序排列，相同count值不覆盖
>     TreeMap<Integer, Tuple2<String, Integer>> treemap = new TreeMap<Integer, Tuple2<String, Integer>>(
>             new Comparator<Integer>() {
>     
>                 @Override
>                 public int compare(Integer y, Integer x) {
>                     return (x < y) ? -1 : 1;
>                 }
>     
>             });
>     
>     //只保留前面TopN个元素
>     
>     for (Tuple2<String, Integer> element : input) {
>         treemap.put(element.f1, element);
>         if (treemap.size() > topSize) {
>             treemap.pollLastEntry();
>         }
>     }
>     
>     
>     for (Map.Entry<Integer, Tuple2<String, Integer>> entry : treemap
>             .entrySet()) {
>         out.collect("=================\n热销图书列表:\n" + new Timestamp(System.currentTimeMillis()) + treemap.toString() + "\n===============\n");
>     }