Best practice to validate null and empty collection in Java

问题

I want to verify whether a collection is empty and null. Could anyone please let me know the best practice.

Currently, I am checking as below:

if (null == sampleMap || sampleMap.isEmpty()) {
  // do something
} 
else {
  // do something else
}

回答1:

If you use the Apache Commons Collections library in your project, you may use the CollectionUtils.isEmpty and MapUtils.isEmpty() methods which respectively check if a collection or a map is empty or null (i.e. they are "null-safe").

The code behind these methods is more or less what user @icza has written in his answer.

Regardless of what you do, remember that the less code you write, the less code you need to test as the complexity of your code decreases.

回答2:

That is the best way to check it. You could write a helper method to do it:

public static boolean isNullOrEmpty( final Collection< ? > c ) {
    return c == null || c.isEmpty();
}

public static boolean isNullOrEmpty( final Map< ?, ? > m ) {
    return m == null || m.isEmpty();
}

回答3:

If you use Spring frameworks, then you can use CollectionUtils to check against both Collections (List, Array) and Map etc.

if(CollectionUtils.isEmpty(...)) {...}

回答4:

Personally, I prefer to use empty collections instead of null and have the algorithms work in a way that for the algorithm it does not matter if the collection is empty or not.

回答5:

When you use spring then you can use

boolean isNullOrEmpty = org.springframework.util.ObjectUtils.isEmpty(obj);

where obj is any [map,collection,array,aythink...]

otherwise: the code is:

public static boolean isEmpty(Object[] array) {
    return (array == null || array.length == 0);
}

public static boolean isEmpty(Object obj) {
    if (obj == null) {
        return true;
    }

    if (obj.getClass().isArray()) {
        return Array.getLength(obj) == 0;
    }
    if (obj instanceof CharSequence) {
        return ((CharSequence) obj).length() == 0;
    }
    if (obj instanceof Collection) {
        return ((Collection) obj).isEmpty();
    }
    if (obj instanceof Map) {
        return ((Map) obj).isEmpty();
    }

    // else
    return false;
}

for String best is:

boolean isNullOrEmpty = (str==null || str.trim().isEmpty());

回答6:

If you need to check for null, that is the way. However, if you have control on this, just return empty collection, whenever you can, and check only for empty later on.

This thread is about the same thing with C#, but the principles applies equally well to java. Like mentioned there, null should be returned only if

null might mean something more specific;

your API (contract) might force you to return null.

回答7:

You can use org.apache.commons.lang.Validate's "notEmpty" method:

Validate.notEmpty(myCollection) -> Validate that the specified argument collection is neither null nor a size of zero (no elements); otherwise throwing an exception.

回答8:

For all the collections including map use: isEmpty method which is there on these collection objects. But you have to do a null check before:

Map<String, String> map;

........
if(map!=null && !map.isEmpty())
......

来源：https://stackoverflow.com/questions/12721076/best-practice-to-validate-null-and-empty-collection-in-java

标签

java

collections