Java Stream_Don't apply filter if my filter string is null

Question

I have 3 filters but they are not always filled with values!

for example:

a=1, b=2, c=null

and I have this for filtering:

myList.stream()
      .filter(item->item.a == a)
      .filter(item->item.b == b)
      .filter(item->item.c == c)
      .Collect(collection.asList);

But it does not work for me. I need the c parameter and its filter to be ignored if my input for c is null like this:

 myList.stream()
       .filter(item->item.a == a)
       .filter(item->item.b == b)
       .Collect(collection.asList);

And whenever each other filter is null, it should be removed from filter's chain like c in previous example.

So change the implementation of your predicate so that it always returns true if c is null. And please, when you ask a question, post real code. Not pseudo-code. — JB Nizet
– JB Nizet, Commented Nov 25, 2019 at 16:08
Thanks@Holger, I think its inverse of my problem, the matter is null input! not the null attribute of object — MohammadMH
– MohammadMH, Commented Nov 26, 2019 at 7:10

Naman · Accepted Answer · 2019-11-26 01:03:56Z

3

For the condition to become valid, it needs the constant to be null or the item's value equal to the constant. This would look like:

myList.stream()
      .filter(item -> a == null || item.a == a)
      .filter(item -> b == null || item.b == b)
      .filter(item -> c == null || item.c == c)
      .collect(Collectors.toList());

edited Nov 26, 2019 at 1:03

Naman

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answered Nov 25, 2019 at 18:30

azro

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Comments

Anonymous · Accepted Answer · 2019-11-26 12:44:05Z

2

My version:

myList.stream()
        .filter(item -> a == null ? true : item.a.equals(a))
        .filter(item -> b == null ? true : item.b.equals(b))
        .filter(item -> c == null ? true : item.c.equals(c))
        .collect(Collectors.toList());

When a filter method returns true, it doesn't filter anything out. If a, b and c are references, as a rule you should use equals() for comparison, not ==.

answered Nov 26, 2019 at 12:44

Anonymous

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