springMVC源码分析--动态样式ThemeResolver（二）

在上一篇博客springMVC源码分析--动态样式ThemeResolver（一）中我们介绍了多样式ThemeResolver的使用方法，接下来我们对源码进行简单的分析一下。

ThemeResolver的体系结构如下：

1、接口ThemeResolver中定义的接口是比较简单的，提供两个接口：

（1）resolveThemeName获取样式名

（2）setThemeName设置样式名

public interface ThemeResolver {

	/**
	 * Resolve the current theme name via the given request.
	 * Should return a default theme as fallback in any case.
	 * @param request request to be used for resolution
	 * @return the current theme name
	 */
	String resolveThemeName(HttpServletRequest request);

	/**
	 * Set the current theme name to the given one.
	 * @param request request to be used for theme name modification
	 * @param response response to be used for theme name modification
	 * @param themeName the new theme name
	 * @throws UnsupportedOperationException if the ThemeResolver implementation
	 * does not support dynamic changing of the theme
	 */
	void setThemeName(HttpServletRequest request, HttpServletResponse response, String themeName);

}

2、抽象类AbstractThemeResolver，提供两个方法：

（1）setDefaultThemeName 设置默认的样式名

（2）getDefaultThemeName 获取默认的样式名

public abstract class AbstractThemeResolver implements ThemeResolver {

	public final static String ORIGINAL_DEFAULT_THEME_NAME = "theme";

	private String defaultThemeName = ORIGINAL_DEFAULT_THEME_NAME;

	public void setDefaultThemeName(String defaultThemeName) {
		this.defaultThemeName = defaultThemeName;
	}

	public String getDefaultThemeName() {
		return this.defaultThemeName;
	}

}

3、实现类CookieThemeResolver，其实现原理其实是比较简单的，就是在Cookie中设置样式名

（1）在setThemeName函数中中将theme设置到cookie中

public class CookieThemeResolver extends CookieGenerator implements ThemeResolver {

	public final static String ORIGINAL_DEFAULT_THEME_NAME = "theme";

	/**
	 * Name of the request attribute that holds the theme name. Only used
	 * for overriding a cookie value if the theme has been changed in the
	 * course of the current request! Use RequestContext.getTheme() to
	 * retrieve the current theme in controllers or views.
	 * @see org.springframework.web.servlet.support.RequestContext#getTheme
	 */
	public static final String THEME_REQUEST_ATTRIBUTE_NAME = CookieThemeResolver.class.getName() + ".THEME";

	public static final String DEFAULT_COOKIE_NAME = CookieThemeResolver.class.getName() + ".THEME";

	private String defaultThemeName = ORIGINAL_DEFAULT_THEME_NAME;

	public CookieThemeResolver() {
		setCookieName(DEFAULT_COOKIE_NAME);
	}

	/**
	 * Set the name of the default theme.
	 */
	public void setDefaultThemeName(String defaultThemeName) {
		this.defaultThemeName = defaultThemeName;
	}

	/**
	 * Return the name of the default theme.
	 */
	public String getDefaultThemeName() {
		return defaultThemeName;
	}

	@Override
	public String resolveThemeName(HttpServletRequest request) {
		// Check request for preparsed or preset theme.
		String themeName = (String) request.getAttribute(THEME_REQUEST_ATTRIBUTE_NAME);
		if (themeName != null) {
			return themeName;
		}

		// Retrieve cookie value from request.
		Cookie cookie = WebUtils.getCookie(request, getCookieName());
		if (cookie != null) {
			String value = cookie.getValue();
			if (StringUtils.hasText(value)) {
				themeName = value;
			}
		}

		// Fall back to default theme.
		if (themeName == null) {
			themeName = getDefaultThemeName();
		}
		request.setAttribute(THEME_REQUEST_ATTRIBUTE_NAME, themeName);
		return themeName;
	}

	@Override
	public void setThemeName(HttpServletRequest request, HttpServletResponse response, String themeName) {
		if (StringUtils.hasText(themeName)) {
			// Set request attribute and add cookie.
			request.setAttribute(THEME_REQUEST_ATTRIBUTE_NAME, themeName);
			addCookie(response, themeName);
		}
		else {
			// Set request attribute to fallback theme and remove cookie.
			request.setAttribute(THEME_REQUEST_ATTRIBUTE_NAME, getDefaultThemeName());
			removeCookie(response);
		}
	}

}

3、实现类SessionThemeResolver的实现也是比较简单的，就是将themeName保存到session中就可以了。

public class SessionThemeResolver extends AbstractThemeResolver {

	/**
	 * Name of the session attribute that holds the theme name.
	 * Only used internally by this implementation.
	 * Use {@code RequestContext(Utils).getTheme()}
	 * to retrieve the current theme in controllers or views.
	 * @see org.springframework.web.servlet.support.RequestContext#getTheme
	 * @see org.springframework.web.servlet.support.RequestContextUtils#getTheme
	 */
	public static final String THEME_SESSION_ATTRIBUTE_NAME = SessionThemeResolver.class.getName() + ".THEME";

	@Override
	public String resolveThemeName(HttpServletRequest request) {
		String themeName = (String) WebUtils.getSessionAttribute(request, THEME_SESSION_ATTRIBUTE_NAME);
		// A specific theme indicated, or do we need to fallback to the default?
		return (themeName != null ? themeName : getDefaultThemeName());
	}

	@Override
	public void setThemeName(HttpServletRequest request, HttpServletResponse response, String themeName) {
		WebUtils.setSessionAttribute(request, THEME_SESSION_ATTRIBUTE_NAME,
				(StringUtils.hasText(themeName) ? themeName : null));
	}

}

4、FixedThemeResolver中没有具体的实现操作

public class FixedThemeResolver extends AbstractThemeResolver {

	@Override
	public String resolveThemeName(HttpServletRequest request) {
		return getDefaultThemeName();
	}

	@Override
	public void setThemeName(HttpServletRequest request, HttpServletResponse response, String themeName) {
		throw new UnsupportedOperationException("Cannot change theme - use a different theme resolution strategy");
	}

}