Primefaces 15: Dynamically set theme

Question

How can I dynamically set a Primefaces theme? Ultimately, I'd like to be able for my application to toggle from dark mode to light mode, depending on the users' OS setting.

ThemeBean.java:

import jakarta.enterprise.context.SessionScoped;
import jakarta.inject.Named;
import java.io.Serializable;
@Named
@SessionScoped
public class ThemeBean implements Serializable {
 private String theme;
 public String getTheme() {
 return theme;
 }
 public void setTheme(String theme) {
 this.theme = theme;
 }
}

web.xml:

 <context-param>
 <param-name>primefaces.THEME</param-name>
 <param-value>#{themeBean.theme}</param-value>
 </context-param>

pom.xml:

 <dependency>
 <groupId>org.primefaces</groupId>
 <artifactId>primefaces-themes</artifactId>
 <version>15.0.10</version>
 </dependency>

However, I keep getting this message:

Error Unable to find resource primefaces-, theme.css

I understand web.xml doesn't support EL expressions mentioned here; however, PrimeFaces showcases uses this approach:

Automatically sets a light or dark theme based on the OS settings. Put it in your template like:

<pe:lightSwitch selected="\#{userBean.theme}"/>

userBean should be a session scoped bean with a String type theme property (with both getter and setter). Then set the theme in your web.xml like:

<context-param>
 <param-name>primefaces.THEME</param-name>
 <param-value>\#{userBean.theme}</param-value>
</context-param>

• Melloware: Couple of questions why the "\" in front of the "#"? Second why using @ManagedBeans and not CDI beans?
• hamster: 1. I guess it was a typo from the showcase. 2. Good point However, even then, I get the same message: Error Unable to find resource primefaces-, theme.css
• Melloware: Maybe download and run the showcase? It definitely theme switches?