How Can I Access Java/Servlet/JSP/JSTL/EL Variables in JavaScript?

Accessing Java / Servlet / JSP / JSTL / EL Variables in JavaScript

In JSP environments, you may encounter scenarios where you need to access Java, Servlet, JSP, JSTL, or EL variables within JavaScript code. This article explores various techniques to achieve this.

Method 1: Printing Variables Directly

Since Java/JSP primarily generates HTML/CSS/JS code, you can leverage JSP to print Java variables as if they were JavaScript variables. Using EL expressions like ${foo}, you can output the variable in the following formats:

<script>var foo = '${foo}';</script>
<script>someFunction('${foo}');</script>

Method 2: JSON Conversion

For complex Java objects such as beans, lists, or maps, you can use JSON libraries like Gson to convert them into JSON strings. This eliminates the need to quote the output in JavaScript code:

String someObjectAsJson = new Gson().toJson(someObject);

<script>var foo = ${someObjectAsJson};</script>

Method 3: Instantiating Custom EL Functions for JS Escaping

When using user-controlled input, it's essential to consider XSS attack vulnerabilities. You can create custom EL functions to escape Java variables for safe usage in JavaScript.

Conclusion

By employing these techniques, you can effectively access Java and other server-side variables within JavaScript code in JSP environments, enabling seamless communication between the server and browser.

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