java - regex for string checking for not null

Question

I need a Java regular expression, which checks that the given String is not Empty and not null . However the expression should ingnore if the user has accidentally given whitespace in the beginning of the input, but allow whitespaces later on.

Answer 1

You could do it without using regex.

boolean check(String s) {
  return s != null && s.trim().length() > 0;
}

Answer 2

You can use Guava to check for nullity and emptiness:

Strings.isNullOrEmpty(myString);

And you cannot use regular expressions on a null String.

Answer 3

Try this:

yourString != null && yourString.trim().length() > 0

Answer 4

您无法在 Java 中使用正则表达式检查空引用。您必须单独检查引用不为空，然后将字符串与正则表达式进行比较。

public static boolean isNullEmptyOrWhitespace(String s) {
  return (s==null) || s.matches("^\\s*$");
}