更新 '_posts/常用的代码块.md'

_posts/常用的代码块.md

@@ -62,6 +62,8 @@ private static Map<String, Object> sortByKey(Map<String, Object> map) {
     //2 按照多个字段
     Map<String, List<Object>> groupBy = objectList.stream().collect(Collectors
     .groupingBy(o -> o.getAttr1() + "_" + o.getAttr2()));
+    
+    Set<Long> attrs = list.stream().map(Object::getAttr).collect(Collectors.toSet());
 
 ```