Java集合中移除所有的null值

Java集合中移除所有的null值
https://blog.csdn.net/qq_36135928/article/details/86605104

org.apache.commons.collections.subtract方法只能移除第一个null元素。

public class CollectionRemoveNullTest {


@Test

public void test() {

List<String> nullList = new ArrayList<>();

nullList.add("a");

nullList.add(null);

nullList.add("b");

nullList.add("c");

nullList.add(null);



Collection&lt;String&gt; removeNull = subtract(nullList, Arrays.asList((String) null));
Iterator&lt;String&gt; it = removeNull.iterator();
while (it.hasNext()) {
  String s = it.next();
  assertTrue(s != null);
}




}




/**





Returns a new {@link Collection} containing <tt><i>a</i> - <i>b</i></tt>.


The cardinality of each element <i>e</i> in the returned


will be the cardinality of <i>e</i> in <i>a</i> minus the cardinality of


<i>e</i> in <i>b</i>, or zero, whichever is greater.




@param a




     the collection to subtract from, must not be null





@param b




     the collection to subtract, must not be null





@return a new collection with the results


@see Collection#removeAll

*/

public static Collection subtract(final Collection a, final Collection b) {

ArrayList list = new ArrayList(a);

for (Iterator it = b.iterator(); it.hasNext()😉 {

list.remove(it.next());

}

return list;

}





}


Collection&lt;String&gt; removeNull = subtract(nullList, Arrays.asList((String) null));
Iterator&lt;String&gt; it = removeNull.iterator();
while (it.hasNext()) {
  String s = it.next();
  assertTrue(s != null);
}
     the collection to subtract from, must not be null
     the collection to subtract, must not be null

自定义方法，移除一个集合中所有的null值

public class CollectionRemoveNullTest {


@Test

public void test() {

List<String> nullList = new ArrayList<>();

nullList.add("a");

nullList.add(null);

nullList.add("b");

nullList.add("c");

nullList.add(null);



Collection&lt;String&gt; removeNull = removeNull(nullList);
Iterator&lt;String&gt; it = removeNull.iterator();
while (it.hasNext()) {
  String s = it.next();
  assertTrue(s != null);
}




}




/**





移除指定集合中的所有null值。




@param source




     待移除null的集合,禁止传入null。





@return 新的结果集合。

*/

public static <T> Collection<T> removeNull(final Collection<T> source) {

assertArgumentNotNull(source, "source");




ArrayList&lt;T&gt; list = new ArrayList&lt;&gt;(source.size());

for (T value : source) {
  if (value != null) {
    list.add(value);
  }
}
return list;




}




/**





断言参数不是null，若是null将抛出异常。




@param argument




     参数。





@param argumentName




     参数名。





@throws IllegalArgumentException




      当参数argument为null时抛出。





@since 1.17

*/

public static void assertArgumentNotNull(Object argument, String argumentName)

throws IllegalArgumentException {

if (argument == null) {

throw new IllegalArgumentException("指定集合不能为空");

}

}

}



Collection&lt;String&gt; removeNull = removeNull(nullList);
Iterator&lt;String&gt; it = removeNull.iterator();
while (it.hasNext()) {
  String s = it.next();
  assertTrue(s != null);
}
     待移除null的集合,禁止传入null。
ArrayList&lt;T&gt; list = new ArrayList&lt;&gt;(source.size());

for (T value : source) {
  if (value != null) {
    list.add(value);
  }
}
return list;
     参数。
     参数名。
      当参数argument为null时抛出。