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");
}

}