/*
 * Copyright 2012-2019 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.boot.web.embedded.tomcat;

import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.TreeMap;
import java.util.stream.Stream;

import javax.servlet.ServletException;

import org.apache.catalina.Container;
import org.apache.catalina.LifecycleException;
import org.apache.catalina.Manager;
import org.apache.catalina.Wrapper;
import org.apache.catalina.core.StandardContext;
import org.apache.catalina.core.StandardWrapper;
import org.apache.catalina.session.ManagerBase;

import org.springframework.boot.web.server.WebServerException;
import org.springframework.util.ClassUtils;

Tomcat StandardContext used by TomcatWebServer to support deferred initialization. 
Author:
Phillip Webb, Andy Wilkinson/**
 * Tomcat {@link StandardContext} used by {@link TomcatWebServer} to support deferred
 * initialization.
 *
 * @author Phillip Webb
 * @author Andy Wilkinson
 */
class TomcatEmbeddedContext extends StandardContext {

	private TomcatStarter starter;

	@Override
	public boolean loadOnStartup(Container[] children) {
		// deferred until later (see deferredLoadOnStartup)
		return true;
	}

	@Override
	public void setManager(Manager manager) {
		if (manager instanceof ManagerBase) {
			manager.setSessionIdGenerator(new LazySessionIdGenerator());
		}
		super.setManager(manager);
	}

	void deferredLoadOnStartup() throws LifecycleException {
		doWithThreadContextClassLoader(getLoader().getClassLoader(),
				() -> getLoadOnStartupWrappers(findChildren()).forEach(this::load));
	}

	private Stream<Wrapper> getLoadOnStartupWrappers(Container[] children) {
		Map<Integer, List<Wrapper>> grouped = new TreeMap<>();
		for (Container child : children) {
			Wrapper wrapper = (Wrapper) child;
			int order = wrapper.getLoadOnStartup();
			if (order >= 0) {
				grouped.computeIfAbsent(order, (o) -> new ArrayList<>()).add(wrapper);
			}
		}
		return grouped.values().stream().flatMap(List::stream);
	}

	private void load(Wrapper wrapper) {
		try {
			wrapper.load();
		}
		catch (ServletException ex) {
			String message = sm.getString("standardContext.loadOnStartup.loadException", getName(), wrapper.getName());
			if (getComputedFailCtxIfServletStartFails()) {
				throw new WebServerException(message, ex);
			}
			getLogger().error(message, StandardWrapper.getRootCause(ex));
		}
	}

	
Some older Servlet frameworks (e.g. Struts, BIRT) use the Thread context class
loader to create servlet instances in this phase. If they do that and then try to
initialize them later the class loader may have changed, so wrap the call to
loadOnStartup in what we think its going to be the main webapp classloader at
runtime.
Params:
classLoader – the class loader to use
code – the code to run/**
	 * Some older Servlet frameworks (e.g. Struts, BIRT) use the Thread context class
	 * loader to create servlet instances in this phase. If they do that and then try to
	 * initialize them later the class loader may have changed, so wrap the call to
	 * loadOnStartup in what we think its going to be the main webapp classloader at
	 * runtime.
	 * @param classLoader the class loader to use
	 * @param code the code to run
	 */
	private void doWithThreadContextClassLoader(ClassLoader classLoader, Runnable code) {
		ClassLoader existingLoader = (classLoader != null) ? ClassUtils.overrideThreadContextClassLoader(classLoader)
				: null;
		try {
			code.run();
		}
		finally {
			if (existingLoader != null) {
				ClassUtils.overrideThreadContextClassLoader(existingLoader);
			}
		}
	}

	void setStarter(TomcatStarter starter) {
		this.starter = starter;
	}

	TomcatStarter getStarter() {
		return this.starter;
	}

}