Themes

You can apply Spring Web MVC framework themes to set the overall look-and-feel of your application, thereby enhancing user experience. A theme is a collection of static resources, typically style sheets and images, that affect the visual style of the application.

as of 6.0 support for themes has been deprecated theme in favor of using CSS, and without any special support on the server side.

Defining a theme

To use themes in your web application, you must set up an implementation of the org.springframework.ui.context.ThemeSource interface. The WebApplicationContext interface extends ThemeSource but delegates its responsibilities to a dedicated implementation. By default, the delegate is an org.springframework.ui.context.support.ResourceBundleThemeSource implementation that loads properties files from the root of the classpath. To use a custom ThemeSource implementation or to configure the base name prefix of the ResourceBundleThemeSource, you can register a bean in the application context with the reserved name, themeSource. The web application context automatically detects a bean with that name and uses it.

When you use the ResourceBundleThemeSource, a theme is defined in a simple properties file. The properties file lists the resources that make up the theme, as the following example shows:

styleSheet=/themes/cool/style.css
background=/themes/cool/img/coolBg.jpg

The keys of the properties are the names that refer to the themed elements from view code. For a JSP, you typically do this using the spring:theme custom tag, which is very similar to the spring:message tag. The following JSP fragment uses the theme defined in the previous example to customize the look and feel:

<%@ taglib prefix="spring" uri="http://www.springframework.org/tags"%>
<html>
	<head>
		<link rel="stylesheet" href="<spring:theme code='styleSheet'/>" type="text/css"/>
	</head>
	<body style="background=<spring:theme code='background'/>">
		...
	</body>
</html>

By default, the ResourceBundleThemeSource uses an empty base name prefix. As a result, the properties files are loaded from the root of the classpath. Thus, you would put the cool.properties theme definition in a directory at the root of the classpath (for example, in /WEB-INF/classes). The ResourceBundleThemeSource uses the standard Java resource bundle loading mechanism, allowing for full internationalization of themes. For example, we could have a /WEB-INF/classes/cool_nl.properties that references a special background image with Dutch text on it.

Resolving Themes

After you define themes, as described in the preceding section, you decide which theme to use. The DispatcherServlet looks for a bean named themeResolver to find out which ThemeResolver implementation to use. A theme resolver works in much the same way as a LocaleResolver. It detects the theme to use for a particular request and can also alter the request’s theme. The following table describes the theme resolvers provided by Spring:

Table 1. ThemeResolver implementations
Class	Description
`FixedThemeResolver`	Selects a fixed theme, set by using the `defaultThemeName` property.
`SessionThemeResolver`	The theme is maintained in the user’s HTTP session. It needs to be set only once for each session but is not persisted between sessions.
`CookieThemeResolver`	The selected theme is stored in a cookie on the client.

Spring also provides a ThemeChangeInterceptor that lets theme changes on every request with a simple request parameter.