Evaluate empty or null JSTL c tags

Question

How can I validate if a String is null or empty using the c tags of JSTL   I have a variable of name var1 and I can display it  but I want to add a comparator to validate it    lt c out value    var1     gt    I want to validate when it is null or empty  my values are strings

User · Answer

This code is correct but if you entered a lot of space (' ') instead of null or empty string return false.

To correct this use regular expresion (this code below check if the variable is null or empty or blank the same as org.apache.commons.lang.StringUtils.isNotBlank) :

<%@ taglib uri="http://java.sun.com/jsp/jstl/functions" prefix="fn" %>
        <c:if test="${not empty description}">
            <c:set var="description" value="${fn:replace(description, ' ', '')}" />
            <c:if test="${not empty description}">
                  The description is not blank.
            </c:if>
        </c:if>

User · Answer

Here s the one liner    Ternary operator inside EL    empty value  value is empty or null   value is NOT empty or null

User · Answer

Here s an example of how to validate a int and a String that you pass from the Java Controller to the JSP file    MainController java    RequestMapping value   ImportJavaToJSP   public ModelAndView getImportJavaToJSP         ModelAndView model2  new ModelAndView  importJavaToJSPExamples         int someNumberValue 6      String someStringValue  abcdefg         model2 addObject  someNumber   someNumberValue       model2 addObject  someString   someStringValue        return model2      importJavaToJSPExamples jsp   lt    taglib prefix  c  uri  http   java sun com jsp jstl core   gt   lt p gt   someNumber  lt  p gt   lt c if test    not empty someNumber   gt       lt p gt someNumber is Not Empty lt  p gt   lt  c if gt   lt c if test    empty someNumber   gt       lt p gt someNumber is Empty lt  p gt   lt  c if gt   lt p gt   someString  lt  p gt   lt c if test    not empty someString   gt       lt p gt someString is Not Empty lt  p gt   lt  c if gt   lt c if test    empty someString   gt       lt p gt someString is Empty lt  p gt   lt  c if gt

User · Answer

In this step I have Set the variable first    lt c set var  structureId  value   lt   article getStructureId    gt   scope  request  gt  lt  c set gt   In this step I have checked the variable empty or not     lt c if test    not empty structureId    gt       lt a href  javascript void 0    gt Change Design lt  a gt    lt  c if gt

User · Answer

if you check only null or empty then you can use the  with default option for this    lt c out default  var1 is empty or null    value    var1    gt

User · Answer

You can use         var    null    alternatively

User · Answer

How can I validate if a String is null or empty using the c tags of JSTL   You can use the empty keyword in a  lt c if gt  for this   lt c if test  quot   empty var1  quot  gt      var1 is empty or null   lt  c if gt   lt c if test  quot   not empty var1  quot  gt      var1 is NOT empty or null   lt  c if gt   Or the  lt c choose gt    lt c choose gt       lt c when test  quot   empty var1  quot  gt          var1 is empty or null       lt  c when gt       lt c otherwise gt          var1 is NOT empty or null       lt  c otherwise gt   lt  c choose gt   Or if you don t need to conditionally render a bunch of tags and thus you could only check it inside a tag attribute  then you can use the EL conditional operator   condition  valueIfTrue   valueIfFalse    lt c out value  quot   empty var1    var1 is empty or null     var1 is NOT empty or null   quot    gt   To learn more about those     things  the Expression Language  which is a separate subject from JSTL   check here  See also   How does EL empty operator work in JSF

User · Answer

to also check blank string  I suggest following   lt    taglib prefix  fn  uri  http   java sun com jsp jstl functions   gt   lt    taglib prefix  c  uri  http   java sun com jsp jstl core   gt    lt c if test    empty fn trim var1    gt    lt  c if gt    It also handles nulls

[jsp] Evaluate empty or null JSTL c tags

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