/*
 * Copyright 2002-2019 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.config.annotation;

import java.util.Collections;

import javax.servlet.ServletContext;

import org.springframework.core.Ordered;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.web.servlet.DispatcherServlet;
import org.springframework.web.servlet.handler.SimpleUrlHandlerMapping;
import org.springframework.web.servlet.resource.DefaultServletHttpRequestHandler;

Configures a request handler for serving static resources by forwarding the request to the Servlet container's "default" Servlet. This is intended to be used when the Spring MVC DispatcherServlet is mapped to "/" thus overriding the Servlet container's default handling of static resources. 
Since this handler is configured at the lowest precedence, effectively
it allows all other handler mappings to handle the request, and if none
of them do, this handler can forward it to the "default" Servlet.
Author:
Rossen Stoyanchev, Juergen Hoeller
See Also:
DefaultServletHttpRequestHandler
Since:
3.1/**
 * Configures a request handler for serving static resources by forwarding
 * the request to the Servlet container's "default" Servlet. This is intended
 * to be used when the Spring MVC {@link DispatcherServlet} is mapped to "/"
 * thus overriding the Servlet container's default handling of static resources.
 *
 * <p>Since this handler is configured at the lowest precedence, effectively
 * it allows all other handler mappings to handle the request, and if none
 * of them do, this handler can forward it to the "default" Servlet.
 *
 * @author Rossen Stoyanchev
 * @author Juergen Hoeller
 * @since 3.1
 * @see DefaultServletHttpRequestHandler
 */
public class DefaultServletHandlerConfigurer {

	private final ServletContext servletContext;

	@Nullable
	private DefaultServletHttpRequestHandler handler;


	
Create a DefaultServletHandlerConfigurer instance. 
Params:
servletContext – the ServletContext to use./**
	 * Create a {@link DefaultServletHandlerConfigurer} instance.
	 * @param servletContext the ServletContext to use.
	 */
	public DefaultServletHandlerConfigurer(ServletContext servletContext) {
		Assert.notNull(servletContext, "ServletContext is required");
		this.servletContext = servletContext;
	}


	
Enable forwarding to the "default" Servlet.
When this method is used the DefaultServletHttpRequestHandler will try to autodetect the "default" Servlet name. Alternatively, you can specify the name of the default Servlet via enable(String). 
See Also:
DefaultServletHttpRequestHandler/**
	 * Enable forwarding to the "default" Servlet.
	 * <p>When this method is used the {@link DefaultServletHttpRequestHandler}
	 * will try to autodetect the "default" Servlet name. Alternatively, you can
	 * specify the name of the default Servlet via {@link #enable(String)}.
	 * @see DefaultServletHttpRequestHandler
	 */
	public void enable() {
		enable(null);
	}

	
Enable forwarding to the "default" Servlet identified by the given name.
This is useful when the default Servlet cannot be autodetected,
for example when it has been manually configured.
See Also:
DefaultServletHttpRequestHandler/**
	 * Enable forwarding to the "default" Servlet identified by the given name.
	 * <p>This is useful when the default Servlet cannot be autodetected,
	 * for example when it has been manually configured.
	 * @see DefaultServletHttpRequestHandler
	 */
	public void enable(@Nullable String defaultServletName) {
		this.handler = new DefaultServletHttpRequestHandler();
		if (defaultServletName != null) {
			this.handler.setDefaultServletName(defaultServletName);
		}
		this.handler.setServletContext(this.servletContext);
	}


	
Return a handler mapping instance ordered at Ordered.LOWEST_PRECEDENCE containing the DefaultServletHttpRequestHandler instance mapped to "/**"; or null if default servlet handling was not been enabled. 
Since:
4.3.12/**
	 * Return a handler mapping instance ordered at {@link Ordered#LOWEST_PRECEDENCE}
	 * containing the {@link DefaultServletHttpRequestHandler} instance mapped
	 * to {@code "/**"}; or {@code null} if default servlet handling was not
	 * been enabled.
	 * @since 4.3.12
	 */
	@Nullable
	protected SimpleUrlHandlerMapping buildHandlerMapping() {
		if (this.handler == null) {
			return null;
		}
		return new SimpleUrlHandlerMapping(Collections.singletonMap("/**", this.handler),
				Ordered.LOWEST_PRECEDENCE);
	}

}