Check whether a string is not null and not empty

Question

How can I check whether a string is not null and not empty?

public void doStuff(String str)
{
    if (str != null && str != \"**here I want to check          


        

Answer 1

Simply, to ignore white space as well:

if (str == null || str.trim().length() == 0) {
    // str is empty
} else {
    // str is not empty
}

Answer 2

Use org.apache.commons.lang.StringUtils

I like to use Apache commons-lang for these kinds of things, and especially the StringUtils utility class:

import org.apache.commons.lang.StringUtils;

if (StringUtils.isNotBlank(str)) {
    ...
} 

if (StringUtils.isBlank(str)) {
    ...
} 

Answer 3

There is a new method in java-11: String#isBlank

Returns true if the string is empty or contains only white space codepoints, otherwise false.

jshell> "".isBlank()
$7 ==> true

jshell> " ".isBlank()
$8 ==> true

jshell> " ! ".isBlank()
$9 ==> false

This could be combined with Optional to check if string is null or empty

boolean isNullOrEmpty = Optional.ofNullable(str).map(String::isBlank).orElse(true);

String#isBlank

Answer 4

test equals with an empty string and null in the same conditional:

if(!"".equals(str) && str != null) {
    // do stuff.
}

Does not throws NullPointerException if str is null, since Object.equals() returns false if arg is null.

the other construct str.equals("") would throw the dreaded NullPointerException. Some might consider bad form using a String literal as the object upon wich equals() is called but it does the job.

Also check this answer: https://stackoverflow.com/a/531825/1532705

Answer 5

You can use StringUtils.isEmpty(), It will result true if the string is either null or empty.

 String str1 = "";
 String str2 = null;

 if(StringUtils.isEmpty(str)){
     System.out.println("str1 is null or empty");
 }

 if(StringUtils.isEmpty(str2)){
     System.out.println("str2 is null or empty");
 }

will result in

str1 is null or empty

str2 is null or empty

Answer 6

The better way to handle null in the string is,

str!=null && !str.equalsIgnoreCase("null") && !str.isEmpty()

In short,

str.length()>0 && !str.equalsIgnoreCase("null")