更新 '_posts/常用的代码块.md'

_posts/常用的代码块.md

@@ -35,8 +35,11 @@ private static Map<String, Object> sortByKey(Map<String, Object> map) {
 ### list 对象根据某个字段分组 .
 
 ``` Java
-
+    //1 按照某个字段
     Map<Object,List<Object>> map = demoList.stream().collect(Collectors.groupingBy(Object::getAttr));
+    //2 按照多个字段
+    Map<String, List<Object>> groupBy = objectList.stream().collect(Collectors
+    .groupingBy(o -> o.getApplyId() + "_" + o.getSkuId()));
 
 ```
 
@@ -49,5 +52,6 @@ private static Map<String, Object> sortByKey(Map<String, Object> map) {
     //根据对象某个属性排序
     List<Object> sortList = objectList.stream().sorted(Comparator.comparing(Object::getAttr)
     .reversed()).collect(Collectors.toList());
-
+    
+    
 ```