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  amp  amp  str       here I want to check the  str  is empty or not                      handle empty string

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What about isEmpty      if str    null  amp  amp   str isEmpty      Be sure to use the parts of  amp  amp  in this order  because java will not proceed to evaluate the second part if the first part of  amp  amp  fails  thus ensuring you will not get a null pointer exception from str isEmpty   if str is null   Beware  it s only available since Java SE 1 6  You have to check str length      0 on previous versions     To ignore whitespace as well   if str    null  amp  amp   str trim   isEmpty       since Java 11 str trim   isEmpty   can be reduced to str isBlank   which will also test for other Unicode white spaces   Wrapped in a handy function   public static boolean empty  final String s          Null-safe  short-circuit evaluation    return s    null    s trim   isEmpty        Becomes   if   empty  str

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With Java 8 Optional you can do   public Boolean isStringCorrect String str        return Optional ofNullable str               map String  trim               map string - gt   str isEmpty                 orElse false       In this expression  you will handle Strings that consist of spaces as well

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str    null  amp  amp  str length      0   alternatively  str    null  amp  amp   str equals       or  str    null  amp  amp      equals str    Note  The second check  first and second alternatives  assumes str is not null  It s ok only because the first check is doing that  and Java doesn t does the second check if the first is false    IMPORTANT  DON T use    for string equality     checks the pointer is equal  not the value  Two strings can be in different memory addresses  two instances  but have the same value

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Use Apache StringUtils  isNotBlank method like   StringUtils isNotBlank str    It will return true only if the str is not null and is not empty

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Almost every library I know defines a utility class called StringUtils  StringUtil or StringHelper  and they usually include the method you are looking for   My personal favorite is Apache Commons   Lang  where in the StringUtils class  you get both the    StringUtils isEmpty String  and the StringUtils isBlank String  method    The first checks whether a string is null or empty  the second checks whether it is null  empty or whitespace only   There are similar utility classes in Spring  Wicket and lots of other libs  If you don t use external libraries  you might want to introduce a StringUtils class in your own project      Update  many years have passed  and these days I d recommend using Guava s Strings isNullOrEmpty string  method

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If you don t want to include the whole library  just include the code you want from it   You ll have to maintain it yourself  but it s a pretty straight forward function   Here it is copied from commons apache org              lt p gt Checks if a String is whitespace  empty      or null  lt  p gt         lt pre gt     StringUtils isBlank null         true    StringUtils isBlank              true    StringUtils isBlank              true    StringUtils isBlank  bob         false    StringUtils isBlank    bob       false     lt  pre gt         param str  the String to check  may be null     return  lt code gt true lt  code gt  if the String is null  empty or whitespace     since 2 0     public static boolean isBlank String str        int strLen      if  str    null     strLen   str length       0            return true            for  int i   0  i  lt  strLen  i              if   Character isWhitespace str charAt i      false                 return false                      return true

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To add to  BJorn and  SeanPatrickFloyd The Guava way to do this is    Strings nullToEmpty str  isEmpty        or Strings isNullOrEmpty str     Commons Lang is more readable at times but I have been slowly relying more on Guava plus sometimes Commons Lang is confusing when it comes to isBlank    as in what is whitespace or not    Guava s version of Commons Lang isBlank would be   Strings nullToEmpty str  trim   isEmpty     I will say code that doesn t allow     empty  AND null is suspicious and potentially buggy in that it probably doesn t handle all cases where is not allowing null makes sense  although for SQL I can understand as SQL HQL is weird about

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Simply  to ignore white space as well   if  str    null    str trim   length      0           str is empty   else          str is not empty

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Just adding Android in here   import android text TextUtils   if   TextUtils isEmpty str

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I ve made my own utility function to check several strings at once  rather than having an if statement full of if str    null  amp  amp   str isEmpty  amp  amp  str2    null  amp  amp   str2 isEmpty   This is the function   public class StringUtils       public static boolean areSet String    strings                for String s   strings              if s    null    s isEmpty                  return false           return true                so I can simply write   if  StringUtils areSet firstName lastName address          do something

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If you are using Spring Boot then below code will do the Job  StringUtils hasLength str

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In case you are using Java 8 and want to have a more Functional Programming approach  you can define a Function that manages the control and then you can reuse it and apply   whenever is needed   Coming to practice  you can define the Function as   Function lt String  Boolean gt  isNotEmpty   s - gt  s    null  amp  amp      equals s    Then  you can use it by simply calling the apply   method as   String emptyString       isNotEmpty apply emptyString      this will return false  String notEmptyString    StackOverflow   isNotEmpty apply notEmptyString      this will return true   If you prefer  you can define a Function that checks if the String is empty and then negate it with     In this case  the Function will look like as    Function lt String  Boolean gt  isEmpty   s - gt  s    null       equals s    Then  you can use it by simply calling the apply   method as   String emptyString        isEmpty apply emptyString      this will return false  String notEmptyString    StackOverflow    isEmpty apply notEmptyString      this will return true

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You should use org apache commons lang3 StringUtils isNotBlank   or org apache commons lang3 StringUtils isNotEmpty  The decision between these two is based on what you actually want to check for    The isNotBlank   checks that the input parameter is     not Null  not the empty string      not a sequence of whitespace characters            The isNotEmpty   checks only that the input parameter is    not null not the Empty String

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To check on if all the string attributes in an object is empty Instead of using   null on all the field names following java reflection api approach    private String name1  private String name2  private String name3   public boolean isEmpty           for  Field field   this getClass   getDeclaredFields              try               field setAccessible true               if  field get this     null                    return false                          catch  Exception e                System out println  Exception occurred in processing                        return true      This method would return true if all the String field values are blank It would return false if any one values is present in the String attributes

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As seanizer said above  Apache StringUtils is fantastic for this  if you were to include guava you should do the following   public List lt Employee gt  findEmployees String str  int dep     Preconditions checkState StringUtils isNotBlank str    Invalid input  input is blank or null         code here         May I also recommend that you refer to the columns in your result set by name rather than by index  this will make your code much easier to maintain

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In case you need to validate your method parameters you can use follow simple method  public class StringUtils        static boolean anyEmptyString String     strings            return Stream of strings  anyMatch s - gt  s    null    s isEmpty                Example   public String concatenate String firstName  String lastName        if StringUtils anyBlankString firstName  lastName             throw new IllegalArgumentException  Empty field found              return firstName         lastName

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test equals with an empty string and null in the same conditional   if     equals str   amp  amp  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

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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

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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

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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 gt   quot  quot  isBlank    7    gt  true  jshell gt   quot   quot  isBlank    8    gt  true  jshell gt   quot     quot  isBlank    9    gt  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

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I would advise Guava or Apache Commons according to your actual need  Check the different behaviors in my example code   import com google common base Strings  import org apache commons lang StringUtils          Created by hu0983 on 2016 01 13       public class StringNotEmptyTesting     public static void main String   args           String a                 String b               String c null       System out println  Apache         if  StringUtils isNotBlank a            System out println   a is blank              if  StringUtils isNotBlank b            System out println   b is blank              if  StringUtils isNotBlank c            System out println   c is blank              System out println  Google          if Strings isNullOrEmpty Strings emptyToNull a             System out println   a is NullOrEmpty              if Strings isNullOrEmpty b            System out println   b is NullOrEmpty              if Strings isNullOrEmpty c            System out println   c is NullOrEmpty                  Result  Apache   a is blank  b is blank  c is blank Google   b is NullOrEmpty  c is NullOrEmpty

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If you use Spring framework then you can use method   org springframework util StringUtils isEmpty  Nullable Object str     This method accepts any Object as an argument  comparing it to null and the empty String  As a consequence  this method will never return true for a non-null non-String object

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How about   if str   null  amp  amp  str length      0

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import android text TextUtils   if   TextUtils isEmpty str    str equalsIgnoreCase

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Simple solution     private boolean stringNotEmptyOrNull String st        return st    null  amp  amp   st isEmpty

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I ve encountered a situation where I must check that  null   as a string  must be regarded as empty  Also white space and an actual null must return true  I ve finally settled on the following function     public boolean isEmpty String testString      return   null  testString        equals     testString  trim        null  equals     testString  toLowerCase

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Returns true or false based on input  Predicate lt String gt  p    s - gt    s    null  amp  amp   s isEmpty     p test string

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The better way to handle null in the string is   str  null  amp  amp   str equalsIgnoreCase  null    amp  amp   str isEmpty     In short   str length   gt 0  amp  amp   str equalsIgnoreCase  null

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This works for me   import com google common base Strings   if   Strings isNullOrEmpty myString            return myString         Returns true if the given string is null or is the empty string       Consider normalizing your string references with nullToEmpty  If you   do  you can use String isEmpty   instead of this method  and you won t   need special null-safe forms of methods like String toUpperCase   either  Or  if you d like to normalize  in the other direction     converting empty strings to null  you can use emptyToNull

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For completeness  If you are already using the Spring framework  the StringUtils provide the method  org springframework util StringUtils hasLength String str       Returns    true if the String is not null and has length   as well as the method  org springframework util StringUtils hasText String str       Returns    true if the String is not null  its length is greater than 0  and it does not contain whitespace only

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To check if a string is not empty you can check if it is null but this doesn t account for a string with whitespace  You could use str trim   to trim all the whitespace and then chain  isEmpty   to ensure that the result is not empty      if str    null  amp  amp   str trim   isEmpty         do your stuffs here

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It is a bit too late  but here is a functional style of checking   Optional ofNullable str       filter s - gt    s trim   isEmpty          ifPresent result - gt              your query setup goes here

[java] Check whether a string is not null and not empty

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