精尽 Spring MVC 源码解析 —— ThemeResolver 组件

ThemeResolver 实际使用很少，所以艿艿也没特别细看。

这里艿艿就转载 IAMTJW 的《Spring MVC 源码分析 —— 动态样式ThemeResolver（二）》。

1. 概述

在上一篇博客《Spring MVC 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。

2. 类图

ThemeResolver 的体系结构如下： ThemeResolver 类图

3. ThemeResolver

接口 ThemeResolver 中定义的接口是比较简单的，提供两个接口：

（1）#resolveThemeName 方法，获取样式名。
（2）#setThemeName 方法，设置样式名。

public interface ThemeResolver {

	/**
     * 从请求中，解析出使用的主题。例如，从请求头 User-Agent ，判断使用 PC 端，还是移动端的主题
     *
	 * 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);

	/**
     * 设置请求，所使用的主题。
     *
	 * 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 ({@code null} or empty to reset it)
	 * @throws UnsupportedOperationException if the ThemeResolver implementation
	 * does not support dynamic changing of the theme
	 */
	void setThemeName(HttpServletRequest request, @Nullable HttpServletResponse response, @Nullable String themeName);

}

4. AbstractThemeResolver

抽象类 AbstractThemeResolver ，提供两个方法：

（1）#setDefaultThemeName(...) 方法，设置默认的样式名。
（2）#getDefaultThemeName(...) 方法，获取默认的样式名。

public abstract class AbstractThemeResolver implements ThemeResolver {

	/**
	 * Out-of-the-box value for the default theme name: "theme".
	 */
	public static final 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;
	}

}

}

5. SessionThemeResolver

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, @Nullable HttpServletResponse response, @Nullable String themeName) {
		WebUtils.setSessionAttribute(request, THEME_SESSION_ATTRIBUTE_NAME,
				(StringUtils.hasText(themeName) ? themeName : null));
	}

}

6. FixedThemeResolver

实现 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, @Nullable HttpServletResponse response, @Nullable String themeName) {
		throw new UnsupportedOperationException("Cannot change theme - use a different theme resolution strategy");
	}

}

7. CookieThemeResolver

实现类 CookieThemeResolver 的实现也是比较简单的，就是将themeName 保存到 Cookie 中就可以了。

public class CookieThemeResolver extends CookieGenerator implements ThemeResolver {

	/**
	 * The default theme name used if no alternative is provided.
	 */
	public static final 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";

	/**
	 * The default name of the cookie that holds the theme name.
	 */
	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 this.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.
		String cookieName = getCookieName();
		if (cookieName != null) {
			Cookie cookie = WebUtils.getCookie(request, cookieName);
			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, @Nullable HttpServletResponse response, @Nullable String themeName) {

		Assert.notNull(response, "HttpServletResponse is required for CookieThemeResolver");

		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);
		}
	}

}

666. 彩蛋

没有彩蛋~

参考和推荐如下文章：

韩路彪《看透 Spring MVC：源代码分析与实践》的「第19章 ThemeResolver」小节