What is the best way to assign a value to a JSTL variable using JavaScript?

Question

What is the best way to assign a value to a JSTL variable using JavaScript?

What is the process to assign a value to a JSTL variable using JavaScript?

<script>

 function function1()

 { 

  var val1 = document.getElementById('userName').value;

  <c:set var="user" value=""/>  // how can I set val1 here?   

 }
 </script>

Is there a way to set the 'user' variable (JSTL) with the value of 'val1' (JavaScript)?

javascript jsp jstl

Answer 1

Answer №1

The execution of JSP and JavaScript in different environments (server side for JSP, client side for JavaScript) makes it impossible for them to be executed in the order they appear in your code.

var val1 = document.getElementById('userName').value; 

<c:set var="user" value=""/>  // How can I set val1 here?

When JSTL code is executed at the server side, the server treats JavaScript/HTML codes as plain texts. Any generated content from the JSTL code will be included in the resulting HTML alongside your other JavaScript/HTML codes. However, the browser only renders HTML and executes JavaScript codes without any knowledge of JSTL code.

For instance,

<script type="text/javascript">
<c:set var="message" value="Hello"/> 
var message = '<c:out value="${message}"/>';
</script>

When this content is being rendered by the browser, it looks like:

<script type="text/javascript">
var message = 'Hello';
</script>

I hope this explanation clarifies things for you.

Answer 2

The execution of JSP and JavaScript in different environments (server side for JSP, client side for JavaScript) makes it impossible for them to be executed in the order they appear in your code.

var val1 = document.getElementById('userName').value; 

<c:set var="user" value=""/>  // How can I set val1 here?

When JSTL code is executed at the server side, the server treats JavaScript/HTML codes as plain texts. Any generated content from the JSTL code will be included in the resulting HTML alongside your other JavaScript/HTML codes. However, the browser only renders HTML and executes JavaScript codes without any knowledge of JSTL code.

For instance,

<script type="text/javascript">
<c:set var="message" value="Hello"/> 
var message = '<c:out value="${message}"/>';
</script>

When this content is being rendered by the browser, it looks like:

<script type="text/javascript">
var message = 'Hello';
</script>

I hope this explanation clarifies things for you.

Answer 3

Answer №2

Here is another method to implement.

To begin, establish the following on any part of the webpage:

<div id="dataHolderId">${anotherValue}</div>

Then, in JavaScript, simply execute something like this:

var anotherValue = $('#dataHolderId').html();

This technique works effectively for scenarios where all scripts are contained within .js files and JSTL is not accessible.

Answer 4

Here is another method to implement.

To begin, establish the following on any part of the webpage:

<div id="dataHolderId">${anotherValue}</div>

Then, in JavaScript, simply execute something like this:

var anotherValue = $('#dataHolderId').html();

This technique works effectively for scenarios where all scripts are contained within .js files and JSTL is not accessible.

Answer 5

Answer №3

<script ...
  function(){
   let dynamicVariable = "<c:out value='${dynamicValueFromServer}'/>";

  }
</script>

This solution functions properly regardless of the absence of a concealed or visible input field defined within the JSP.

Answer 6

<script ...
  function(){
   let dynamicVariable = "<c:out value='${dynamicValueFromServer}'/>";

  }
</script>

This solution functions properly regardless of the absence of a concealed or visible input field defined within the JSP.

Answer 7

Answer №4

Avoid the temptation to write code within code. Instead, consider using a JSON object or variable in your programming. Avoid hardcoding JavaScript functions with JSTL provided variables for better organization and readability. Generating JSON can be beneficial, but be cautious not to overcomplicate things unnecessarily.

Imagine the frustration of trying to decipher JavaScript code where parameters are being set within a client-side class. It can lead to confusion and inefficiency. Focus on passing data back and forth effectively without resorting to generating actual code snippets within your scripts.

Answer 8

Avoid the temptation to write code within code. Instead, consider using a JSON object or variable in your programming. Avoid hardcoding JavaScript functions with JSTL provided variables for better organization and readability. Generating JSON can be beneficial, but be cautious not to overcomplicate things unnecessarily.

Imagine the frustration of trying to decipher JavaScript code where parameters are being set within a client-side class. It can lead to confusion and inefficiency. Focus on passing data back and forth effectively without resorting to generating actual code snippets within your scripts.

Answer 9

Answer №5

My response is negative when it comes to accessing values from jstl in JavaScript. However, one can still use JavaScript to display the user's name. Here are some effective methods: To showcase the user's name, if your HTML contains:

<div id="uName"></div>

You can exhibit the user's name using the following code.

var val1 = document.getElementById('userName').value;
document.getElementById('uName').innerHTML = val1;

For extracting data from jstl into your JavaScript :

var userName = '<c:out value="${user}"/>';

here ${user} represents the data received as a response (from the backend).

Assigning number/array length

var arrayLength = <c:out value="${details.size()}"/>;

Advanced Techniques

function advanced(){
    var values = new Array();
    <c:if test="${empty details.users}">
       values.push("No user found"); 
    </c:if>         

    <c:if test="${!empty details.users}">
        <c:forEach var="user" items="${details.users}" varStatus="stat">
            values.push("${user.name}");   
        </c:forEach>
    </:c:if>
    alert("values[0] "+values[0]);

});

Answer 10

My response is negative when it comes to accessing values from jstl in JavaScript. However, one can still use JavaScript to display the user's name. Here are some effective methods: To showcase the user's name, if your HTML contains:

<div id="uName"></div>

You can exhibit the user's name using the following code.

var val1 = document.getElementById('userName').value;
document.getElementById('uName').innerHTML = val1;

For extracting data from jstl into your JavaScript :

var userName = '<c:out value="${user}"/>';

here ${user} represents the data received as a response (from the backend).

Assigning number/array length

var arrayLength = <c:out value="${details.size()}"/>;

Advanced Techniques

function advanced(){
    var values = new Array();
    <c:if test="${empty details.users}">
       values.push("No user found"); 
    </c:if>         

    <c:if test="${!empty details.users}">
        <c:forEach var="user" items="${details.users}" varStatus="stat">
            values.push("${user.name}");   
        </c:forEach>
    </:c:if>
    alert("values[0] "+values[0]);

});

Answer 11

Answer №6

To properly concatenate strings in XML, it is important to ensure that the resulting string is valid XML format. A good practice for writing XML can be found at this resource . Alternatively, you may consider using a JavaScript API like helma's XmlWriter to simplify the process.

Answer 12

To properly concatenate strings in XML, it is important to ensure that the resulting string is valid XML format. A good practice for writing XML can be found at this resource . Alternatively, you may consider using a JavaScript API like helma's XmlWriter to simplify the process.

Answer 13

Answer №7

To set this particular variable, utilize value="${val1}" within the c:set tag when incorporating jQuery into your platform.

Answer 14

To set this particular variable, utilize value="${val1}" within the c:set tag when incorporating jQuery into your platform.

Answer 15

Answer №8

To transform the entire JSTL object into a JavaScript object, you can use the JSON conversion method provided by Jackson in Java.

import com.fasterxml.jackson.databind.ObjectMapper;

public class JsonUtil{
   public static String convertToJsonString(Object obj){
      ObjectMapper objectMapper = ...; // Jackson object mapper
      return objectMapper.writeValueAsString(obj);
   }
}

/WEB-INF/tags/util-functions.tld:

<?xml version="1.0" encoding="ISO-8859-1" ?>
<taglib xmlns="http://java.sun.com/xml/ns/j2ee" 
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
  xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/javaee/web-jsptaglibrary_2_1.xsd" 
  version="2.1"> 

  <tlib-version>1.0</tlib-version>
  <uri>http://www.your.url/util-functions</uri>

  <function>
      <name>convertToJsonString</name>
      <function-class>your.package.JsonUtil</function-class>
      <function-signature>java.lang.String convertToJsonString(java.lang.Object)</function-signature>
  </function>  

</taglib>

web.xml

<jsp-config>
  <tablib>
    <taglib-uri>http://www.your.url/util-functions</taglib-uri>
    <taglib-location>/WEB-INF/tags/util-functions.tld</taglib-location>
  </taglib>
</jsp-confi>

mypage.jsp:

<%@ taglib prefix="uf" uri="http://www.your.url/util-functions" %> 

<script>
   var myJavaScriptObject = JSON.parse('${uf:convertToJsonString(myJstlObject)}');
</script>

Answer 16

To transform the entire JSTL object into a JavaScript object, you can use the JSON conversion method provided by Jackson in Java.

import com.fasterxml.jackson.databind.ObjectMapper;

public class JsonUtil{
   public static String convertToJsonString(Object obj){
      ObjectMapper objectMapper = ...; // Jackson object mapper
      return objectMapper.writeValueAsString(obj);
   }
}

/WEB-INF/tags/util-functions.tld:

<?xml version="1.0" encoding="ISO-8859-1" ?>
<taglib xmlns="http://java.sun.com/xml/ns/j2ee" 
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
  xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/javaee/web-jsptaglibrary_2_1.xsd" 
  version="2.1"> 

  <tlib-version>1.0</tlib-version>
  <uri>http://www.your.url/util-functions</uri>

  <function>
      <name>convertToJsonString</name>
      <function-class>your.package.JsonUtil</function-class>
      <function-signature>java.lang.String convertToJsonString(java.lang.Object)</function-signature>
  </function>  

</taglib>

web.xml

<jsp-config>
  <tablib>
    <taglib-uri>http://www.your.url/util-functions</taglib-uri>
    <taglib-location>/WEB-INF/tags/util-functions.tld</taglib-location>
  </taglib>
</jsp-confi>

mypage.jsp:

<%@ taglib prefix="uf" uri="http://www.your.url/util-functions" %> 

<script>
   var myJavaScriptObject = JSON.parse('${uf:convertToJsonString(myJstlObject)}');
</script>

What is the best way to assign a value to a JSTL variable using JavaScript?

Answer №1

Answer №2

Answer №3

Answer №4

Answer №5

For extracting data from jstl into your JavaScript :

Assigning number/array length

Advanced Techniques

Answer №6

Answer №7

Answer №8

/WEB-INF/tags/util-functions.tld:

web.xml

mypage.jsp:

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