Jakarta Commons Cookbook

2.2. Checking for an Empty String

Problem

You need to test for an empty or null string.

Solution

Use StringUtils.isBlank() . This method will return true if it is supplied with an empty, zero length, or whitespace-only string. This method gracefully handles a null input by returning true. The following example demonstrates isBlank( ) with four strings:

String test = "";
String test2 = "\n\n\t";
String test3 = null;
String test4 = "Test";

System.out.println( "test blank? " + StringUtils.isBlank( test ) );
System.out.println( "test2 blank? " + StringUtils.isBlank( test2 ) );
System.out.println( "test3 blank? " + StringUtils.isBlank( test3 ) );
System.out.println( "test4 blank? " + StringUtils.isBlank( test4 ) );

All four strings are tested, and the following output is produced:

test blank? true
test2 blank? true
test3 blank? true
test4 blank? false

Discussion

Checking for nonblank strings is just as easy; StringUtils.isNotBlank( ) will return the compliment of isBlank( ). If a string is empty, contains only whitespace, or is null, the StringUtils.isNotBlank( ) method will return false. This method comes in handy when a process expects a certain string to have content, and it gracefully handles a null input by returning false:

String test = "\t\t";
String test2 = "Test";

System.out.println( "test is not blank? " + StringUtils.isNotBlank( test ) );
System.out.println( "test2 is not blank? " + StringUtils.isNotBlank( test2 ) );

This produces the following output, which shows that a string ...