StringUtils.isBlank() vs String.isEmpty()

问题

I ran into some code that has the following:

String foo = getvalue(\"foo\");
if (StringUtils.isBlank(foo))
    doStuff();
else
    doOtherStuff();

This appears to be functionally equivalent to the following:

String foo = getvalue(\"foo\");
if (foo.isEmpty())
    doStuff();
else
    doOtherStuff();

Is a difference between the two (org.apache.commons.lang3.StringUtils.isBlank and java.lang.String.isEmpty)?

回答1:

StringUtils.isBlank() checks that each character of the string is a whitespace character (or that the string is empty or that it's null). This is totally different than just checking if the string is empty.

From the linked documentation:

Checks if a String is whitespace, empty ("") or null.

 StringUtils.isBlank(null)      = true
 StringUtils.isBlank("")        = true  
 StringUtils.isBlank(" ")       = true  
 StringUtils.isBlank("bob")     = false  
 StringUtils.isBlank("  bob  ") = false

For comparison StringUtils.isEmpty:

 StringUtils.isEmpty(null)      = true
 StringUtils.isEmpty("")        = true  
 StringUtils.isEmpty(" ")       = false  
 StringUtils.isEmpty("bob")     = false  
 StringUtils.isEmpty("  bob  ") = false

Warning: In java.lang.String.isBlank() and java.lang.String.isEmpty() work the same except they don't return true for null.

java.lang.String.isBlank()

java.lang.String.isEmpty()

回答2:

The accepted answer from @arshajii is totally correct. However just being more explicit by saying below,

StringUtils.isBlank()

 StringUtils.isBlank(null)      = true
 StringUtils.isBlank("")        = true  
 StringUtils.isBlank(" ")       = true  
 StringUtils.isBlank("bob")     = false  
 StringUtils.isBlank("  bob  ") = false

StringUtils.isEmpty

 StringUtils.isEmpty(null)      = true
 StringUtils.isEmpty("")        = true  
 StringUtils.isEmpty(" ")       = false  
 StringUtils.isEmpty("bob")     = false  
 StringUtils.isEmpty("  bob  ") = false

回答3:

StringUtils isEmpty = String isEmpty checks + checks for null.

StringUtils isBlank = StringUtils isEmpty checks + checks if the text contains only whitespace character(s).

Useful links for further investigation:

StringUtils isBlank documentation
StringUtils isEmpty documentation
String isEmpty documentation

回答4:

StringUtils.isBlank() will also check for null, whereas this:

String foo = getvalue("foo");
if (foo.isEmpty())

will throw a NullPointerException if foo is null.

回答5:

StringUtils.isBlank also returns true for just whitespace:

isBlank(String str)

Checks if a String is whitespace, empty ("") or null.

回答6:

StringUtils.isBlank(foo) will perform a null check for you. If you perform foo.isEmpty() and foo is null, you will raise a NullPointerException.

回答7:

StringUtils.isBlank() returns true for blanks(just whitespaces)and for null String as well. Actually it trims the Char sequences and then performs check.

StringUtils.isEmpty() returns true when there is no charsequence in the String parameter or when String parameter is null. Difference is that isEmpty() returns false if String parameter contains just whiltespaces. It considers whitespaces as a state of being non empty.

回答8:

public static boolean isEmpty(String ptext) {
 return ptext == null || ptext.trim().length() == 0;
}

public static boolean isBlank(String ptext) {
 return ptext == null || ptext.trim().length() == 0;
}

Both have the same code how will isBlank handle white spaces probably you meant isBlankString this has the code for handling whitespaces.

public static boolean isBlankString( String pString ) {
 int strLength;
 if( pString == null || (strLength = pString.length()) == 0)
 return true;
 for(int i=0; i < strLength; i++)
 if(!Character.isWhitespace(pString.charAt(i)))
 return false;
 return false;
}

回答9:

The only difference between isBlank() and isEmpty() is:

StringUtils.isBlank(" ")       = true //compared string value has space and considered as blank

StringUtils.isEmpty(" ")       = false //compared string value has space and not considered as empty

回答10:

Instead of using third party lib, use Java 11 isBlank()

    String str1 = "";
    String str2 = "   ";
    Character ch = '\u0020';
    String str3 =ch+" "+ch;

    System.out.println(str1.isEmpty()); //true
    System.out.println(str2.isEmpty()); //false
    System.out.println(str3.isEmpty()); //false            

    System.out.println(str1.isBlank()); //true
    System.out.println(str2.isBlank()); //true
    System.out.println(str3.isBlank()); //true

回答11:

I am answering this because it's the top result in Google for "String isBlank() Method".

If you are using Java 11 or above, you can use the String class isBlank() method. This method does the same thing as Apache Commons StringUtils class.

I have written a small post on this method examples, read it here.

来源：https://stackoverflow.com/questions/23419087/stringutils-isblank-vs-string-isempty

标签

java

string

string-utils