/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.servlet;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.lang.Nullable;

Interface for web-based theme resolution strategies that allows for
both theme resolution via the request and theme modification via
request and response.
This interface allows for implementations based on session, cookies, etc. The default implementation is FixedThemeResolver, simply using a configured default theme. 
Note that this resolver is only responsible for determining the
current theme name. The Theme instance for the resolved theme name
gets looked up by DispatcherServlet via the respective ThemeSource,
i.e. the current WebApplicationContext.
Use RequestContext.getTheme() to retrieve the current theme in controllers or views, independent of the actual resolution strategy. 
Author:
Jean-Pierre Pawlak, Juergen Hoeller
See Also:
Theme
ThemeSource
Since:
17.06.2003/**
 * Interface for web-based theme resolution strategies that allows for
 * both theme resolution via the request and theme modification via
 * request and response.
 *
 * <p>This interface allows for implementations based on session,
 * cookies, etc. The default implementation is
 * {@link org.springframework.web.servlet.theme.FixedThemeResolver},
 * simply using a configured default theme.
 *
 * <p>Note that this resolver is only responsible for determining the
 * current theme name. The Theme instance for the resolved theme name
 * gets looked up by DispatcherServlet via the respective ThemeSource,
 * i.e. the current WebApplicationContext.
 *
 * <p>Use {@link org.springframework.web.servlet.support.RequestContext#getTheme()}
 * to retrieve the current theme in controllers or views, independent
 * of the actual resolution strategy.
 *
 * @author Jean-Pierre Pawlak
 * @author Juergen Hoeller
 * @since 17.06.2003
 * @see org.springframework.ui.context.Theme
 * @see org.springframework.ui.context.ThemeSource
 */
public interface ThemeResolver {

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

	
Set the current theme name to the given one.
Params:
request – the request to be used for theme name modification
response – the response to be used for theme name modification
themeName – the new theme name (null or empty to reset it)
Throws:
UnsupportedOperationException – if the ThemeResolver implementation
does not support dynamic changing of the theme/**
	 * Set the current theme name to the given one.
	 * @param request the request to be used for theme name modification
	 * @param response the 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);

}