Theme Resolution

/**
 * Theme resolver that chains multiple resolvers using chain of responsibility pattern
 */
public class ChainingThemeResolver extends AbstractThemeResolver {
    
    /**
     * Default constructor creating empty resolver chain
     */
    public ChainingThemeResolver();
    
    /**
     * Adds resolver to the chain for evaluation
     * @param r Theme resolver to add to the chain
     * @return This ChainingThemeResolver for method chaining
     */
    @CanIgnoreReturnValue
    public ChainingThemeResolver addResolver(ThemeResolver r);
    
    /**
     * Resolves theme name by trying each resolver in chain order
     * @param httpServletRequest HTTP request to resolve theme for
     * @return Theme name from first resolver returning non-default result, or default theme
     */
    @Override
    public String resolveThemeName(@Nonnull HttpServletRequest httpServletRequest);
    
    /**
     * No-op implementation for theme setting - theme is resolved, not set
     * @param httpServletRequest HTTP request
     * @param httpServletResponse HTTP response  
     * @param s Theme name
     */
    @Override
    public void setThemeName(@Nonnull HttpServletRequest httpServletRequest, 
                           HttpServletResponse httpServletResponse, String s);
}

import org.apereo.cas.services.web.ChainingThemeResolver;
import org.springframework.web.servlet.theme.CookieThemeResolver;
import org.springframework.web.servlet.theme.SessionThemeResolver;
import org.springframework.web.servlet.theme.FixedThemeResolver;

// Create chaining resolver
ChainingThemeResolver chainResolver = new ChainingThemeResolver();
chainResolver.setDefaultThemeName("default");

// Add resolvers in priority order
CookieThemeResolver cookieResolver = new CookieThemeResolver();
cookieResolver.setDefaultThemeName("default");
chainResolver.addResolver(cookieResolver);

SessionThemeResolver sessionResolver = new SessionThemeResolver();  
sessionResolver.setDefaultThemeName("default");
chainResolver.addResolver(sessionResolver);

FixedThemeResolver fixedResolver = new FixedThemeResolver();
fixedResolver.setDefaultThemeName("default");
chainResolver.addResolver(fixedResolver);

// Resolve theme for request
String themeName = chainResolver.resolveThemeName(request);

// Example evaluation flow:
// 1. CookieThemeResolver returns "default" -> continue
// 2. SessionThemeResolver returns "dark" -> return "dark"
// 3. Remaining resolvers are not evaluated

// Standard chain configuration (as done by auto-configuration)
chainResolver
    .addResolver(cookieThemeResolver)      // Priority 1
    .addResolver(sessionThemeResolver)     // Priority 2  
    .addResolver(headerThemeResolver)      // Priority 3
    .addResolver(serviceThemeResolver)     // Priority 4
    .addResolver(fixedThemeResolver);      // Priority 5 (fallback)

// Example custom resolver
public class DatabaseThemeResolver extends AbstractThemeResolver {
    @Override
    public String resolveThemeName(HttpServletRequest request) {
        String userId = getUserIdFromRequest(request);
        return userThemeService.getThemeForUser(userId);
    }
    
    @Override
    public void setThemeName(HttpServletRequest request, 
                           HttpServletResponse response, String themeName) {
        // Implement theme persistence if needed
    }
}

// Add to chain
DatabaseThemeResolver dbResolver = new DatabaseThemeResolver();
dbResolver.setDefaultThemeName("default");
chainResolver.addResolver(dbResolver);