Java 8使用条件过滤并收集自定义Map

Question

我有一些集合List<Map<String, Object>>需要使用Java 8 lambda表达式进行过滤。 我将收到带有标志的JSON对象，必须应用过滤条件。如果未收到JSON对象，则不需要过滤。

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
}

现在我正在收集这样的自定义地图：

Map<String, Object> someMap = new LinkedHashMap<>();
someMap.put("someCustomField1", someObject.field1());
someMap.put("someCustomField2", someObject.field2());
someMap.put("someCustomField3", someObject.field3());

Answer 1

试试这个：

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()) ;
}