Java 8過濾條件並收集自定義地圖

Question

我有一些收集List<Map<String, Object>>，需要使用Java 8 lambda表達式進行過濾。 我將收到帶有必須應用過濾標準的標誌的JSON對象。如果沒有收到JSON對象，則不需要過濾。

protected List<Map<String, Object>> populate(List<SomeObject> someObjects, String string) { 
    taskList.stream() 
      // How to put condition here? Ho to skip filter if no filter oprions are received? 
      .filter(someObject -> (if(string != null) someobject.getName == string)) 
      // The second problem is to collect custom map like 
      .collect(Collectors.toMap("customField1"), someObject.getName()) ... // I need somehow put some additional custom fields here 
} 

現在我收集自定義地圖這樣的：

Map<String, Object> someMap = new LinkedHashMap<>(); 
      someMap.put("someCustomField1", someObject.Field1()); 
      someMap.put("someCustomField2", someObject.Field2()); 
      someMap.put("someCustomField3", someObject.Field3()); 

Answer 1

只是檢查，你是否需要應用過濾器或沒有再使用filter方法或不使用它：

protected List<Map<String, Object>> populate(List<SomeObject> someObjects, String string) { 
    Stream<SomeObject> stream = someObjects.stream(); 
    if (string != null) { 
     stream = stream.filter(s -> string.equals(s.getName())); 
    } 
    return stream.map(someObject -> { 
     Map<String, Object> map = new LinkedHashMap<>(); 
     map.put("someCustomField1", someObject.Field1()); 
     map.put("someCustomField2", someObject.Field2()); 
     map.put("someCustomField3", someObject.Field3()); 
     return map; 
    }).collect(Collectors.toList()); 
} 

Answer 2

試試這個：

protected List<Map<String, Object>> populate(List<SomeObject> someObjects, String string) { 
    return someObjects.stream() 
      .filter(someObject -> string == null || string.equals(someObject.getName())) 
      .map(someObject -> 
       new HashMap<String, Object>(){{ 
        put("someCustomField1", someObject.Field1()); 
        put("someCustomField2", someObject.Field2()); 
        put("someCustomField3", someObject.Field3()); 
       }}) 
      .collect(Collectors.toList()) ; 
}