240 lines
7.5 KiB
Markdown
240 lines
7.5 KiB
Markdown
# 精尽 Spring MVC 源码解析 —— ThemeResolver 组件
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> ThemeResolver 实际使用很少，所以艿艿也没特别细看。
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>
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> 这里艿艿就转载 IAMTJW 的 [《Spring MVC 源码分析 —— 动态样式ThemeResolver（二）》](https://blog.csdn.net/qq924862077/article/details/53484532) 。
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# 1. 概述
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在上一篇博客 [《Spring MVC 源码分析 —— 动态样式ThemeResolver（一）》](https://blog.csdn.net/qq924862077/article/details/53438710) 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。
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# 2. 类图
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ThemeResolver 的体系结构如下：[](http://static.iocoder.cn/images/Spring/2022-06-10/01.png)ThemeResolver 类图
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# 3. ThemeResolver
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接口 ThemeResolver 中定义的接口是比较简单的，提供两个接口：
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- （1）`#resolveThemeName` 方法，获取样式名。
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- （2）`#setThemeName` 方法，设置样式名。
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```
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public interface ThemeResolver {
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/**
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* 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
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*
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* Resolve the current theme name via the given request.
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* Should return a default theme as fallback in any case.
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* @param request request to be used for resolution
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* @return the current theme name
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*/
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String resolveThemeName(HttpServletRequest request);
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/**
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* 设置请求，所使用的主题。
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*
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* Set the current theme name to the given one.
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* @param request request to be used for theme name modification
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* @param response response to be used for theme name modification
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* @param themeName the new theme name ({@code null} or empty to reset it)
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* @throws UnsupportedOperationException if the ThemeResolver implementation
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* does not support dynamic changing of the theme
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*/
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void setThemeName(HttpServletRequest request, @Nullable HttpServletResponse response, @Nullable String themeName);
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}
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```
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# 4. AbstractThemeResolver
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抽象类 AbstractThemeResolver ，提供两个方法：
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- （1）`#setDefaultThemeName(...)` 方法，设置默认的样式名。
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- （2）`#getDefaultThemeName(...)` 方法，获取默认的样式名。
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```
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public abstract class AbstractThemeResolver implements ThemeResolver {
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/**
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* Out-of-the-box value for the default theme name: "theme".
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*/
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public static final String ORIGINAL_DEFAULT_THEME_NAME = "theme";
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private String defaultThemeName = ORIGINAL_DEFAULT_THEME_NAME;
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public void setDefaultThemeName(String defaultThemeName) {
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this.defaultThemeName = defaultThemeName;
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}
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public String getDefaultThemeName() {
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return this.defaultThemeName;
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}
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}
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```
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}
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# 5. SessionThemeResolver
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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。
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```
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public class SessionThemeResolver extends AbstractThemeResolver {
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/**
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* Name of the session attribute that holds the theme name.
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* Only used internally by this implementation.
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* Use {@code RequestContext(Utils).getTheme()}
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* to retrieve the current theme in controllers or views.
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* @see org.springframework.web.servlet.support.RequestContext#getTheme
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* @see org.springframework.web.servlet.support.RequestContextUtils#getTheme
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*/
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public static final String THEME_SESSION_ATTRIBUTE_NAME = SessionThemeResolver.class.getName() + ".THEME";
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@Override
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public String resolveThemeName(HttpServletRequest request) {
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String themeName = (String) WebUtils.getSessionAttribute(request, THEME_SESSION_ATTRIBUTE_NAME);
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// A specific theme indicated, or do we need to fallback to the default?
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return (themeName != null ? themeName : getDefaultThemeName());
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}
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@Override
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public void setThemeName(
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HttpServletRequest request, @Nullable HttpServletResponse response, @Nullable String themeName) {
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WebUtils.setSessionAttribute(request, THEME_SESSION_ATTRIBUTE_NAME,
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(StringUtils.hasText(themeName) ? themeName : null));
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}
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}
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```
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# 6. FixedThemeResolver
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实现 FixedThemeResolver 中没有具体的实现操作。
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```
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public class FixedThemeResolver extends AbstractThemeResolver {
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@Override
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public String resolveThemeName(HttpServletRequest request) {
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return getDefaultThemeName();
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}
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@Override
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public void setThemeName(
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HttpServletRequest request, @Nullable HttpServletResponse response, @Nullable String themeName) {
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throw new UnsupportedOperationException("Cannot change theme - use a different theme resolution strategy");
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}
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}
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```
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# 7. CookieThemeResolver
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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。
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```
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public class CookieThemeResolver extends CookieGenerator implements ThemeResolver {
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/**
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* The default theme name used if no alternative is provided.
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*/
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public static final String ORIGINAL_DEFAULT_THEME_NAME = "theme";
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/**
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* Name of the request attribute that holds the theme name. Only used
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* for overriding a cookie value if the theme has been changed in the
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* course of the current request! Use RequestContext.getTheme() to
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* retrieve the current theme in controllers or views.
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* @see org.springframework.web.servlet.support.RequestContext#getTheme
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*/
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public static final String THEME_REQUEST_ATTRIBUTE_NAME = CookieThemeResolver.class.getName() + ".THEME";
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/**
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* The default name of the cookie that holds the theme name.
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*/
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public static final String DEFAULT_COOKIE_NAME = CookieThemeResolver.class.getName() + ".THEME";
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private String defaultThemeName = ORIGINAL_DEFAULT_THEME_NAME;
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public CookieThemeResolver() {
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setCookieName(DEFAULT_COOKIE_NAME);
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}
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/**
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* Set the name of the default theme.
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*/
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public void setDefaultThemeName(String defaultThemeName) {
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this.defaultThemeName = defaultThemeName;
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}
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/**
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* Return the name of the default theme.
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*/
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public String getDefaultThemeName() {
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return this.defaultThemeName;
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}
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@Override
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public String resolveThemeName(HttpServletRequest request) {
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// Check request for preparsed or preset theme.
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String themeName = (String) request.getAttribute(THEME_REQUEST_ATTRIBUTE_NAME);
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if (themeName != null) {
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return themeName;
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}
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// Retrieve cookie value from request.
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String cookieName = getCookieName();
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if (cookieName != null) {
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Cookie cookie = WebUtils.getCookie(request, cookieName);
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if (cookie != null) {
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String value = cookie.getValue();
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if (StringUtils.hasText(value)) {
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themeName = value;
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}
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}
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}
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// Fall back to default theme.
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if (themeName == null) {
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themeName = getDefaultThemeName();
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}
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request.setAttribute(THEME_REQUEST_ATTRIBUTE_NAME, themeName);
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return themeName;
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}
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@Override
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public void setThemeName(
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HttpServletRequest request, @Nullable HttpServletResponse response, @Nullable String themeName) {
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Assert.notNull(response, "HttpServletResponse is required for CookieThemeResolver");
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if (StringUtils.hasText(themeName)) {
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// Set request attribute and add cookie.
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request.setAttribute(THEME_REQUEST_ATTRIBUTE_NAME, themeName);
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addCookie(response, themeName);
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} else {
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// Set request attribute to fallback theme and remove cookie.
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request.setAttribute(THEME_REQUEST_ATTRIBUTE_NAME, getDefaultThemeName());
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removeCookie(response);
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}
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}
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}
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```
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# 666. 彩蛋
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没有彩蛋~
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参考和推荐如下文章：
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- 韩路彪 [《看透 Spring MVC：源代码分析与实践》](https://item.jd.com/11807414.html) 的 [「第19章 ThemeResolver」](https://svip.iocoder.cn/Spring-MVC/ThemeResolver/#) 小节 |