RoyalTiger :
I have an unmodifiable map (Map<String, Object>). This contains a key-value pair, where the value should be a List, but for a specific key the value is an empty List.
How can I remove that empty list from the map and return?
I have done it using predicate which checks if the value is an instance of collection and then check if Collections.isNotEmpty(..).
I want to know is there any better approach than this? (In Java 8)
public class StudentTest {
Predicate<Object> isCollectionNotEmpty = input -> {
if (input instanceof Collection) {
return CommonCollectionUtils.isNotEmpty((Collection<?>)input);
}
return true;
};
Predicate<Object> isObjectNotNull = input -> Objects.nonNull(input);
public static void main(String[] args) {
StudentTest s = new StudentTest();
final Map<String, Object> map1 = new HashMap<>();
map1.put("student_batch_size", 200);
map1.put("student_avg_height", 172);
map1.put("Student_names", Collections.emptyList());
final Map<String, Object> finalMap = s.getFinalMap(Collections.unmodifiableMap(map1));
System.out.println(finalMap);
}
private Map<String, Object> getFinalMap(final Map<String, Object> inputMap) {
final Map<String, Object> resultMap = new HashMap<>();
//inputMap.values().remove(Collections.emptyList());
resultMap.putAll(inputMap.entrySet().stream()
.filter(entry -> isObjectNotNull.and(isCollectionNotEmpty).test(entry.getValue()))
.collect(Collectors.toMap(e -> e.getKey(), e -> e.getValue())));
return resultMap;
}
}
Expected Output:
{student_avg_height=172, student_batch_size=200}
Andrew Tobilko :
Collection#removeIf might be a good option to consider.
private Map<String, Object> getFinalMap(final Map<String, Object> inputMap) {
final Map<String, Object> resultMap = new HashMap<>(inputMap);
resultMap.entrySet().removeIf(e -> e.getValue() instanceof Collection && ((Collection) e.getValue()).isEmpty());
return resultMap;
}
If a stream-based approach is more appealing to you
private Map<String, Object> getFinalMap(final Map<String, Object> inputMap) {
return inputMap.entrySet()
.stream()
.filter(e -> !(e.getValue() instanceof Collection && ((Collection) e.getValue()).isEmpty()))
.collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));
}
UPDATE
If you want to filter out null objects regardless of their type, here are slight changes to the methods mentioned above
1) removeIf
resultMap.entrySet()
.removeIf(e -> Objects.isNull(e.getValue()) ||
(e.getValue() instanceof Collection && ((Collection) e.getValue()).isEmpty());
2) stream-based
.filter(e -> Objects.nonNull(e.getValue()))
.filter(e -> !(e.getValue() instanceof Collection && ((Collection) e.getValue()).isEmpty()))
Guess you like
Origin http://43.154.161.224:23101/article/api/json?id=327169&siteId=1