org.springframework/spring-web/5.1.5.RELEASE : org/springframework/web/util/WebUtils.java

WebUtils
https://github.com/spring-projects/spring-framework: Spring Web (Spring IO)
Apache License, Version 2.0
Juergen Hoeller
/*
 * Copyright 2002-2018 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
 *
 *      http://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.util;

import java.io.File;
import java.io.FileNotFoundException;
import java.net.URI;
import java.util.Collection;
import java.util.Enumeration;
import java.util.Map;
import java.util.StringTokenizer;
import java.util.TreeMap;
import javax.servlet.ServletContext;
import javax.servlet.ServletRequest;
import javax.servlet.ServletRequestWrapper;
import javax.servlet.ServletResponse;
import javax.servlet.ServletResponseWrapper;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpRequest;
import org.springframework.http.server.ServletServerHttpRequest;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.util.CollectionUtils;
import org.springframework.util.LinkedMultiValueMap;
import org.springframework.util.MultiValueMap;
import org.springframework.util.ObjectUtils;
import org.springframework.util.StringUtils;

Miscellaneous utilities for web applications.
Used by various framework classes.
Author: Rod Johnson, Juergen Hoeller, Sebastien Deleuze/**
 * Miscellaneous utilities for web applications.
 * Used by various framework classes.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @author Sebastien Deleuze
 */
public abstract class WebUtils {

	Standard Servlet 2.3+ spec request attribute for include request URI.
If included via a RequestDispatcher, the current resource will see the originating request. Its own request URI is exposed as a request attribute. /**
	 * Standard Servlet 2.3+ spec request attribute for include request URI.
	 * <p>If included via a {@code RequestDispatcher}, the current resource will see the
	 * originating request. Its own request URI is exposed as a request attribute.
	 */
	public static final String INCLUDE_REQUEST_URI_ATTRIBUTE = "javax.servlet.include.request_uri";

	Standard Servlet 2.3+ spec request attribute for include context path.
If included via a RequestDispatcher, the current resource will see the originating context path. Its own context path is exposed as a request attribute. /**
	 * Standard Servlet 2.3+ spec request attribute for include context path.
	 * <p>If included via a {@code RequestDispatcher}, the current resource will see the
	 * originating context path. Its own context path is exposed as a request attribute.
	 */
	public static final String INCLUDE_CONTEXT_PATH_ATTRIBUTE = "javax.servlet.include.context_path";

	Standard Servlet 2.3+ spec request attribute for include servlet path.
If included via a RequestDispatcher, the current resource will see the originating servlet path. Its own servlet path is exposed as a request attribute. /**
	 * Standard Servlet 2.3+ spec request attribute for include servlet path.
	 * <p>If included via a {@code RequestDispatcher}, the current resource will see the
	 * originating servlet path. Its own servlet path is exposed as a request attribute.
	 */
	public static final String INCLUDE_SERVLET_PATH_ATTRIBUTE = "javax.servlet.include.servlet_path";

	Standard Servlet 2.3+ spec request attribute for include path info.
If included via a RequestDispatcher, the current resource will see the originating path info. Its own path info is exposed as a request attribute. /**
	 * Standard Servlet 2.3+ spec request attribute for include path info.
	 * <p>If included via a {@code RequestDispatcher}, the current resource will see the
	 * originating path info. Its own path info is exposed as a request attribute.
	 */
	public static final String INCLUDE_PATH_INFO_ATTRIBUTE = "javax.servlet.include.path_info";

	Standard Servlet 2.3+ spec request attribute for include query string.
If included via a RequestDispatcher, the current resource will see the originating query string. Its own query string is exposed as a request attribute. /**
	 * Standard Servlet 2.3+ spec request attribute for include query string.
	 * <p>If included via a {@code RequestDispatcher}, the current resource will see the
	 * originating query string. Its own query string is exposed as a request attribute.
	 */
	public static final String INCLUDE_QUERY_STRING_ATTRIBUTE = "javax.servlet.include.query_string";

	Standard Servlet 2.4+ spec request attribute for forward request URI.
If forwarded to via a RequestDispatcher, the current resource will see its
own request URI. The originating request URI is exposed as a request attribute.
/**
	 * Standard Servlet 2.4+ spec request attribute for forward request URI.
	 * <p>If forwarded to via a RequestDispatcher, the current resource will see its
	 * own request URI. The originating request URI is exposed as a request attribute.
	 */
	public static final String FORWARD_REQUEST_URI_ATTRIBUTE = "javax.servlet.forward.request_uri";

	Standard Servlet 2.4+ spec request attribute for forward context path.
If forwarded to via a RequestDispatcher, the current resource will see its
own context path. The originating context path is exposed as a request attribute.
/**
	 * Standard Servlet 2.4+ spec request attribute for forward context path.
	 * <p>If forwarded to via a RequestDispatcher, the current resource will see its
	 * own context path. The originating context path is exposed as a request attribute.
	 */
	public static final String FORWARD_CONTEXT_PATH_ATTRIBUTE = "javax.servlet.forward.context_path";

	Standard Servlet 2.4+ spec request attribute for forward servlet path.
If forwarded to via a RequestDispatcher, the current resource will see its
own servlet path. The originating servlet path is exposed as a request attribute.
/**
	 * Standard Servlet 2.4+ spec request attribute for forward servlet path.
	 * <p>If forwarded to via a RequestDispatcher, the current resource will see its
	 * own servlet path. The originating servlet path is exposed as a request attribute.
	 */
	public static final String FORWARD_SERVLET_PATH_ATTRIBUTE = "javax.servlet.forward.servlet_path";

	Standard Servlet 2.4+ spec request attribute for forward path info.
If forwarded to via a RequestDispatcher, the current resource will see its
own path ingo. The originating path info is exposed as a request attribute.
/**
	 * Standard Servlet 2.4+ spec request attribute for forward path info.
	 * <p>If forwarded to via a RequestDispatcher, the current resource will see its
	 * own path ingo. The originating path info is exposed as a request attribute.
	 */
	public static final String FORWARD_PATH_INFO_ATTRIBUTE = "javax.servlet.forward.path_info";

	Standard Servlet 2.4+ spec request attribute for forward query string.
If forwarded to via a RequestDispatcher, the current resource will see its
own query string. The originating query string is exposed as a request attribute.
/**
	 * Standard Servlet 2.4+ spec request attribute for forward query string.
	 * <p>If forwarded to via a RequestDispatcher, the current resource will see its
	 * own query string. The originating query string is exposed as a request attribute.
	 */
	public static final String FORWARD_QUERY_STRING_ATTRIBUTE = "javax.servlet.forward.query_string";

	Standard Servlet 2.3+ spec request attribute for error page status code.
To be exposed to JSPs that are marked as error pages, when forwarding
to them directly rather than through the servlet container's error page
resolution mechanism.
/**
	 * Standard Servlet 2.3+ spec request attribute for error page status code.
	 * <p>To be exposed to JSPs that are marked as error pages, when forwarding
	 * to them directly rather than through the servlet container's error page
	 * resolution mechanism.
	 */
	public static final String ERROR_STATUS_CODE_ATTRIBUTE = "javax.servlet.error.status_code";

	Standard Servlet 2.3+ spec request attribute for error page exception type.
To be exposed to JSPs that are marked as error pages, when forwarding
to them directly rather than through the servlet container's error page
resolution mechanism.
/**
	 * Standard Servlet 2.3+ spec request attribute for error page exception type.
	 * <p>To be exposed to JSPs that are marked as error pages, when forwarding
	 * to them directly rather than through the servlet container's error page
	 * resolution mechanism.
	 */
	public static final String ERROR_EXCEPTION_TYPE_ATTRIBUTE = "javax.servlet.error.exception_type";

	Standard Servlet 2.3+ spec request attribute for error page message.
To be exposed to JSPs that are marked as error pages, when forwarding
to them directly rather than through the servlet container's error page
resolution mechanism.
/**
	 * Standard Servlet 2.3+ spec request attribute for error page message.
	 * <p>To be exposed to JSPs that are marked as error pages, when forwarding
	 * to them directly rather than through the servlet container's error page
	 * resolution mechanism.
	 */
	public static final String ERROR_MESSAGE_ATTRIBUTE = "javax.servlet.error.message";

	Standard Servlet 2.3+ spec request attribute for error page exception.
To be exposed to JSPs that are marked as error pages, when forwarding
to them directly rather than through the servlet container's error page
resolution mechanism.
/**
	 * Standard Servlet 2.3+ spec request attribute for error page exception.
	 * <p>To be exposed to JSPs that are marked as error pages, when forwarding
	 * to them directly rather than through the servlet container's error page
	 * resolution mechanism.
	 */
	public static final String ERROR_EXCEPTION_ATTRIBUTE = "javax.servlet.error.exception";

	Standard Servlet 2.3+ spec request attribute for error page request URI.
To be exposed to JSPs that are marked as error pages, when forwarding
to them directly rather than through the servlet container's error page
resolution mechanism.
/**
	 * Standard Servlet 2.3+ spec request attribute for error page request URI.
	 * <p>To be exposed to JSPs that are marked as error pages, when forwarding
	 * to them directly rather than through the servlet container's error page
	 * resolution mechanism.
	 */
	public static final String ERROR_REQUEST_URI_ATTRIBUTE = "javax.servlet.error.request_uri";

	Standard Servlet 2.3+ spec request attribute for error page servlet name.
To be exposed to JSPs that are marked as error pages, when forwarding
to them directly rather than through the servlet container's error page
resolution mechanism.
/**
	 * Standard Servlet 2.3+ spec request attribute for error page servlet name.
	 * <p>To be exposed to JSPs that are marked as error pages, when forwarding
	 * to them directly rather than through the servlet container's error page
	 * resolution mechanism.
	 */
	public static final String ERROR_SERVLET_NAME_ATTRIBUTE = "javax.servlet.error.servlet_name";

	Prefix of the charset clause in a content type String: ";charset=".
/**
	 * Prefix of the charset clause in a content type String: ";charset=".
	 */
	public static final String CONTENT_TYPE_CHARSET_PREFIX = ";charset=";

	Default character encoding to use when request.getCharacterEncoding returns null, according to the Servlet spec. 
See Also: ServletRequest.getCharacterEncoding/**
	 * Default character encoding to use when {@code request.getCharacterEncoding}
	 * returns {@code null}, according to the Servlet spec.
	 * @see ServletRequest#getCharacterEncoding
	 */
	public static final String DEFAULT_CHARACTER_ENCODING = "ISO-8859-1";

	Standard Servlet spec context attribute that specifies a temporary directory for the current web application, of type java.io.File. /**
	 * Standard Servlet spec context attribute that specifies a temporary
	 * directory for the current web application, of type {@code java.io.File}.
	 */
	public static final String TEMP_DIR_CONTEXT_ATTRIBUTE = "javax.servlet.context.tempdir";

	HTML escape parameter at the servlet context level (i.e. a context-param in web.xml): "defaultHtmlEscape". /**
	 * HTML escape parameter at the servlet context level
	 * (i.e. a context-param in {@code web.xml}): "defaultHtmlEscape".
	 */
	public static final String HTML_ESCAPE_CONTEXT_PARAM = "defaultHtmlEscape";

	Use of response encoding for HTML escaping parameter at the servlet context level (i.e. a context-param in web.xml): "responseEncodedHtmlEscape". 
Since: 4.1.2/**
	 * Use of response encoding for HTML escaping parameter at the servlet context level
	 * (i.e. a context-param in {@code web.xml}): "responseEncodedHtmlEscape".
	 * @since 4.1.2
	 */
	public static final String RESPONSE_ENCODED_HTML_ESCAPE_CONTEXT_PARAM = "responseEncodedHtmlEscape";

	Web app root key parameter at the servlet context level (i.e. a context-param in web.xml): "webAppRootKey". /**
	 * Web app root key parameter at the servlet context level
	 * (i.e. a context-param in {@code web.xml}): "webAppRootKey".
	 */
	public static final String WEB_APP_ROOT_KEY_PARAM = "webAppRootKey";

	Default web app root key: "webapp.root". /** Default web app root key: "webapp.root". */
	public static final String DEFAULT_WEB_APP_ROOT_KEY = "webapp.root";

	Name suffixes in case of image buttons. /** Name suffixes in case of image buttons. */
	public static final String[] SUBMIT_IMAGE_SUFFIXES = {".x", ".y"};

	Key for the mutex session attribute. /** Key for the mutex session attribute. */
	public static final String SESSION_MUTEX_ATTRIBUTE = WebUtils.class.getName() + ".MUTEX";


	Set a system property to the web application root directory. The key of the system property can be defined with the "webAppRootKey" context-param in web.xml. Default is "webapp.root". Can be used for tools that support substitution with System.getProperty values, like log4j's "${key}" syntax within log file locations. 
Params: servletContext – the servlet context of the web application
Throws: IllegalStateException – if the system property is already set,
or if the WAR file is not expanded
See Also: WEB_APP_ROOT_KEY_PARAM
DEFAULT_WEB_APP_ROOT_KEY
WebAppRootListener/**
	 * Set a system property to the web application root directory.
	 * The key of the system property can be defined with the "webAppRootKey"
	 * context-param in {@code web.xml}. Default is "webapp.root".
	 * <p>Can be used for tools that support substitution with {@code System.getProperty}
	 * values, like log4j's "${key}" syntax within log file locations.
	 * @param servletContext the servlet context of the web application
	 * @throws IllegalStateException if the system property is already set,
	 * or if the WAR file is not expanded
	 * @see #WEB_APP_ROOT_KEY_PARAM
	 * @see #DEFAULT_WEB_APP_ROOT_KEY
	 * @see WebAppRootListener
	 */
	public static void setWebAppRootSystemProperty(ServletContext servletContext) throws IllegalStateException {
		Assert.notNull(servletContext, "ServletContext must not be null");
		String root = servletContext.getRealPath("/");
		if (root == null) {
			throw new IllegalStateException(
					"Cannot set web app root system property when WAR file is not expanded");
		}
		String param = servletContext.getInitParameter(WEB_APP_ROOT_KEY_PARAM);
		String key = (param != null ? param : DEFAULT_WEB_APP_ROOT_KEY);
		String oldValue = System.getProperty(key);
		if (oldValue != null && !StringUtils.pathEquals(oldValue, root)) {
			throw new IllegalStateException("Web app root system property already set to different value: '" +
					key + "' = [" + oldValue + "] instead of [" + root + "] - " +
					"Choose unique values for the 'webAppRootKey' context-param in your web.xml files!");
		}
		System.setProperty(key, root);
		servletContext.log("Set web app root system property: '" + key + "' = [" + root + "]");
	}

	Remove the system property that points to the web app root directory.
To be called on shutdown of the web application.
Params: servletContext – the servlet context of the web application
See Also: setWebAppRootSystemProperty/**
	 * Remove the system property that points to the web app root directory.
	 * To be called on shutdown of the web application.
	 * @param servletContext the servlet context of the web application
	 * @see #setWebAppRootSystemProperty
	 */
	public static void removeWebAppRootSystemProperty(ServletContext servletContext) {
		Assert.notNull(servletContext, "ServletContext must not be null");
		String param = servletContext.getInitParameter(WEB_APP_ROOT_KEY_PARAM);
		String key = (param != null ? param : DEFAULT_WEB_APP_ROOT_KEY);
		System.getProperties().remove(key);
	}

	Return whether default HTML escaping is enabled for the web application, i.e. the value of the "defaultHtmlEscape" context-param in web.xml (if any). This method differentiates between no param specified at all and
an actual boolean value specified, allowing to have a context-specific
default in case of no setting at the global level.
Params: servletContext – the servlet context of the web application
Returns: whether default HTML escaping is enabled for the given application (null = no explicit default)/**
	 * Return whether default HTML escaping is enabled for the web application,
	 * i.e. the value of the "defaultHtmlEscape" context-param in {@code web.xml}
	 * (if any).
	 * <p>This method differentiates between no param specified at all and
	 * an actual boolean value specified, allowing to have a context-specific
	 * default in case of no setting at the global level.
	 * @param servletContext the servlet context of the web application
	 * @return whether default HTML escaping is enabled for the given application
	 * ({@code null} = no explicit default)
	 */
	@Nullable
	public static Boolean getDefaultHtmlEscape(@Nullable ServletContext servletContext) {
		if (servletContext == null) {
			return null;
		}
		String param = servletContext.getInitParameter(HTML_ESCAPE_CONTEXT_PARAM);
		return (StringUtils.hasText(param) ? Boolean.valueOf(param) : null);
	}

	Return whether response encoding should be used when HTML escaping characters, thus only escaping XML markup significant characters with UTF-* encodings. This option is enabled for the web application with a ServletContext param, i.e. the value of the "responseEncodedHtmlEscape" context-param in web.xml (if any). This method differentiates between no param specified at all and
an actual boolean value specified, allowing to have a context-specific
default in case of no setting at the global level.
Params: servletContext – the servlet context of the web application
Returns: whether response encoding is to be used for HTML escaping (null = no explicit default)
Since: 4.1.2/**
	 * Return whether response encoding should be used when HTML escaping characters,
	 * thus only escaping XML markup significant characters with UTF-* encodings.
	 * This option is enabled for the web application with a ServletContext param,
	 * i.e. the value of the "responseEncodedHtmlEscape" context-param in {@code web.xml}
	 * (if any).
	 * <p>This method differentiates between no param specified at all and
	 * an actual boolean value specified, allowing to have a context-specific
	 * default in case of no setting at the global level.
	 * @param servletContext the servlet context of the web application
	 * @return whether response encoding is to be used for HTML escaping
	 * ({@code null} = no explicit default)
	 * @since 4.1.2
	 */
	@Nullable
	public static Boolean getResponseEncodedHtmlEscape(@Nullable ServletContext servletContext) {
		if (servletContext == null) {
			return null;
		}
		String param = servletContext.getInitParameter(RESPONSE_ENCODED_HTML_ESCAPE_CONTEXT_PARAM);
		return (StringUtils.hasText(param) ? Boolean.valueOf(param) : null);
	}

	Return the temporary directory for the current web application,
as provided by the servlet container.
Params: servletContext – the servlet context of the web application
Returns: the File representing the temporary directory/**
	 * Return the temporary directory for the current web application,
	 * as provided by the servlet container.
	 * @param servletContext the servlet context of the web application
	 * @return the File representing the temporary directory
	 */
	public static File getTempDir(ServletContext servletContext) {
		Assert.notNull(servletContext, "ServletContext must not be null");
		return (File) servletContext.getAttribute(TEMP_DIR_CONTEXT_ATTRIBUTE);
	}

	Return the real path of the given path within the web application,
as provided by the servlet container.
Prepends a slash if the path does not already start with a slash, and throws a FileNotFoundException if the path cannot be resolved to a resource (in contrast to ServletContext's getRealPath, which returns null). 
Params: servletContext – the servlet context of the web application
path – the path within the web application
Throws: FileNotFoundException – if the path cannot be resolved to a resource
See Also: ServletContext.getRealPath
Returns: the corresponding real path/**
	 * Return the real path of the given path within the web application,
	 * as provided by the servlet container.
	 * <p>Prepends a slash if the path does not already start with a slash,
	 * and throws a FileNotFoundException if the path cannot be resolved to
	 * a resource (in contrast to ServletContext's {@code getRealPath},
	 * which returns null).
	 * @param servletContext the servlet context of the web application
	 * @param path the path within the web application
	 * @return the corresponding real path
	 * @throws FileNotFoundException if the path cannot be resolved to a resource
	 * @see javax.servlet.ServletContext#getRealPath
	 */
	public static String getRealPath(ServletContext servletContext, String path) throws FileNotFoundException {
		Assert.notNull(servletContext, "ServletContext must not be null");
		// Interpret location as relative to the web application root directory.
		if (!path.startsWith("/")) {
			path = "/" + path;
		}
		String realPath = servletContext.getRealPath(path);
		if (realPath == null) {
			throw new FileNotFoundException(
					"ServletContext resource [" + path + "] cannot be resolved to absolute file path - " +
					"web application archive not expanded?");
		}
		return realPath;
	}

	Determine the session id of the given request, if any.
Params: request – current HTTP request
Returns: the session id, or null if none/**
	 * Determine the session id of the given request, if any.
	 * @param request current HTTP request
	 * @return the session id, or {@code null} if none
	 */
	@Nullable
	public static String getSessionId(HttpServletRequest request) {
		Assert.notNull(request, "Request must not be null");
		HttpSession session = request.getSession(false);
		return (session != null ? session.getId() : null);
	}

	Check the given request for a session attribute of the given name.
Returns null if there is no session or if the session has no such attribute.
Does not create a new session if none has existed before!
Params: request – current HTTP request
name – the name of the session attribute
Returns: the value of the session attribute, or null if not found/**
	 * Check the given request for a session attribute of the given name.
	 * Returns null if there is no session or if the session has no such attribute.
	 * Does not create a new session if none has existed before!
	 * @param request current HTTP request
	 * @param name the name of the session attribute
	 * @return the value of the session attribute, or {@code null} if not found
	 */
	@Nullable
	public static Object getSessionAttribute(HttpServletRequest request, String name) {
		Assert.notNull(request, "Request must not be null");
		HttpSession session = request.getSession(false);
		return (session != null ? session.getAttribute(name) : null);
	}

	Check the given request for a session attribute of the given name.
Throws an exception if there is no session or if the session has no such
attribute. Does not create a new session if none has existed before!
Params: request – current HTTP request
name – the name of the session attribute
Throws: IllegalStateException – if the session attribute could not be found
Returns: the value of the session attribute, or null if not found/**
	 * Check the given request for a session attribute of the given name.
	 * Throws an exception if there is no session or if the session has no such
	 * attribute. Does not create a new session if none has existed before!
	 * @param request current HTTP request
	 * @param name the name of the session attribute
	 * @return the value of the session attribute, or {@code null} if not found
	 * @throws IllegalStateException if the session attribute could not be found
	 */
	public static Object getRequiredSessionAttribute(HttpServletRequest request, String name)
			throws IllegalStateException {

		Object attr = getSessionAttribute(request, name);
		if (attr == null) {
			throw new IllegalStateException("No session attribute '" + name + "' found");
		}
		return attr;
	}

	Set the session attribute with the given name to the given value.
Removes the session attribute if value is null, if a session existed at all.
Does not create a new session if not necessary!
Params: request – current HTTP request
name – the name of the session attribute
value – the value of the session attribute/**
	 * Set the session attribute with the given name to the given value.
	 * Removes the session attribute if value is null, if a session existed at all.
	 * Does not create a new session if not necessary!
	 * @param request current HTTP request
	 * @param name the name of the session attribute
	 * @param value the value of the session attribute
	 */
	public static void setSessionAttribute(HttpServletRequest request, String name, @Nullable Object value) {
		Assert.notNull(request, "Request must not be null");
		if (value != null) {
			request.getSession().setAttribute(name, value);
		}
		else {
			HttpSession session = request.getSession(false);
			if (session != null) {
				session.removeAttribute(name);
			}
		}
	}

	Return the best available mutex for the given session:
that is, an object to synchronize on for the given session.
Returns the session mutex attribute if available; usually, this means that the HttpSessionMutexListener needs to be defined in web.xml. Falls back to the HttpSession itself if no mutex attribute found. 
The session mutex is guaranteed to be the same object during the entire lifetime of the session, available under the key defined by the SESSION_MUTEX_ATTRIBUTE constant. It serves as a safe reference to synchronize on for locking on the current session. 
In many cases, the HttpSession reference itself is a safe mutex
as well, since it will always be the same object reference for the
same active logical session. However, this is not guaranteed across
different servlet containers; the only 100% safe way is a session mutex.
Params: session – the HttpSession to find a mutex for
See Also: SESSION_MUTEX_ATTRIBUTE
HttpSessionMutexListener
Returns: the mutex object (never null)/**
	 * Return the best available mutex for the given session:
	 * that is, an object to synchronize on for the given session.
	 * <p>Returns the session mutex attribute if available; usually,
	 * this means that the HttpSessionMutexListener needs to be defined
	 * in {@code web.xml}. Falls back to the HttpSession itself
	 * if no mutex attribute found.
	 * <p>The session mutex is guaranteed to be the same object during
	 * the entire lifetime of the session, available under the key defined
	 * by the {@code SESSION_MUTEX_ATTRIBUTE} constant. It serves as a
	 * safe reference to synchronize on for locking on the current session.
	 * <p>In many cases, the HttpSession reference itself is a safe mutex
	 * as well, since it will always be the same object reference for the
	 * same active logical session. However, this is not guaranteed across
	 * different servlet containers; the only 100% safe way is a session mutex.
	 * @param session the HttpSession to find a mutex for
	 * @return the mutex object (never {@code null})
	 * @see #SESSION_MUTEX_ATTRIBUTE
	 * @see HttpSessionMutexListener
	 */
	public static Object getSessionMutex(HttpSession session) {
		Assert.notNull(session, "Session must not be null");
		Object mutex = session.getAttribute(SESSION_MUTEX_ATTRIBUTE);
		if (mutex == null) {
			mutex = session;
		}
		return mutex;
	}


	Return an appropriate request object of the specified type, if available,
unwrapping the given request as far as necessary.
Params: request – the servlet request to introspect
requiredType – the desired type of request object
Returns: the matching request object, or null if none of that type is available/**
	 * Return an appropriate request object of the specified type, if available,
	 * unwrapping the given request as far as necessary.
	 * @param request the servlet request to introspect
	 * @param requiredType the desired type of request object
	 * @return the matching request object, or {@code null} if none
	 * of that type is available
	 */
	@SuppressWarnings("unchecked")
	@Nullable
	public static <T> T getNativeRequest(ServletRequest request, @Nullable Class<T> requiredType) {
		if (requiredType != null) {
			if (requiredType.isInstance(request)) {
				return (T) request;
			}
			else if (request instanceof ServletRequestWrapper) {
				return getNativeRequest(((ServletRequestWrapper) request).getRequest(), requiredType);
			}
		}
		return null;
	}

	Return an appropriate response object of the specified type, if available,
unwrapping the given response as far as necessary.
Params: response – the servlet response to introspect
requiredType – the desired type of response object
Returns: the matching response object, or null if none of that type is available/**
	 * Return an appropriate response object of the specified type, if available,
	 * unwrapping the given response as far as necessary.
	 * @param response the servlet response to introspect
	 * @param requiredType the desired type of response object
	 * @return the matching response object, or {@code null} if none
	 * of that type is available
	 */
	@SuppressWarnings("unchecked")
	@Nullable
	public static <T> T getNativeResponse(ServletResponse response, @Nullable Class<T> requiredType) {
		if (requiredType != null) {
			if (requiredType.isInstance(response)) {
				return (T) response;
			}
			else if (response instanceof ServletResponseWrapper) {
				return getNativeResponse(((ServletResponseWrapper) response).getResponse(), requiredType);
			}
		}
		return null;
	}

	Determine whether the given request is an include request,
that is, not a top-level HTTP request coming in from the outside.
Checks the presence of the "javax.servlet.include.request_uri"
request attribute. Could check any request attribute that is only
present in an include request.
Params: request – current servlet request
Returns: whether the given request is an include request/**
	 * Determine whether the given request is an include request,
	 * that is, not a top-level HTTP request coming in from the outside.
	 * <p>Checks the presence of the "javax.servlet.include.request_uri"
	 * request attribute. Could check any request attribute that is only
	 * present in an include request.
	 * @param request current servlet request
	 * @return whether the given request is an include request
	 */
	public static boolean isIncludeRequest(ServletRequest request) {
		return (request.getAttribute(INCLUDE_REQUEST_URI_ATTRIBUTE) != null);
	}

	Expose the Servlet spec's error attributes as HttpServletRequest attributes under the keys defined in the Servlet 2.3 specification, for error pages that are rendered directly rather than through the Servlet container's error page resolution: javax.servlet.error.status_code, javax.servlet.error.exception_type, javax.servlet.error.message, javax.servlet.error.exception, javax.servlet.error.request_uri, javax.servlet.error.servlet_name. Does not override values if already present, to respect attribute values
that have been exposed explicitly before.
Exposes status code 200 by default. Set the "javax.servlet.error.status_code"
attribute explicitly (before or after) in order to expose a different status code.
Params: request – current servlet request
ex – the exception encountered
servletName – the name of the offending servlet/**
	 * Expose the Servlet spec's error attributes as {@link javax.servlet.http.HttpServletRequest}
	 * attributes under the keys defined in the Servlet 2.3 specification, for error pages that
	 * are rendered directly rather than through the Servlet container's error page resolution:
	 * {@code javax.servlet.error.status_code},
	 * {@code javax.servlet.error.exception_type},
	 * {@code javax.servlet.error.message},
	 * {@code javax.servlet.error.exception},
	 * {@code javax.servlet.error.request_uri},
	 * {@code javax.servlet.error.servlet_name}.
	 * <p>Does not override values if already present, to respect attribute values
	 * that have been exposed explicitly before.
	 * <p>Exposes status code 200 by default. Set the "javax.servlet.error.status_code"
	 * attribute explicitly (before or after) in order to expose a different status code.
	 * @param request current servlet request
	 * @param ex the exception encountered
	 * @param servletName the name of the offending servlet
	 */
	public static void exposeErrorRequestAttributes(HttpServletRequest request, Throwable ex,
			@Nullable String servletName) {

		exposeRequestAttributeIfNotPresent(request, ERROR_STATUS_CODE_ATTRIBUTE, HttpServletResponse.SC_OK);
		exposeRequestAttributeIfNotPresent(request, ERROR_EXCEPTION_TYPE_ATTRIBUTE, ex.getClass());
		exposeRequestAttributeIfNotPresent(request, ERROR_MESSAGE_ATTRIBUTE, ex.getMessage());
		exposeRequestAttributeIfNotPresent(request, ERROR_EXCEPTION_ATTRIBUTE, ex);
		exposeRequestAttributeIfNotPresent(request, ERROR_REQUEST_URI_ATTRIBUTE, request.getRequestURI());
		if (servletName != null) {
			exposeRequestAttributeIfNotPresent(request, ERROR_SERVLET_NAME_ATTRIBUTE, servletName);
		}
	}

	Expose the specified request attribute if not already present.
Params: request – current servlet request
name – the name of the attribute
value – the suggested value of the attribute/**
	 * Expose the specified request attribute if not already present.
	 * @param request current servlet request
	 * @param name the name of the attribute
	 * @param value the suggested value of the attribute
	 */
	private static void exposeRequestAttributeIfNotPresent(ServletRequest request, String name, Object value) {
		if (request.getAttribute(name) == null) {
			request.setAttribute(name, value);
		}
	}

	Clear the Servlet spec's error attributes as HttpServletRequest attributes under the keys defined in the Servlet 2.3 specification: javax.servlet.error.status_code, javax.servlet.error.exception_type, javax.servlet.error.message, javax.servlet.error.exception, javax.servlet.error.request_uri, javax.servlet.error.servlet_name. 
Params: request – current servlet request/**
	 * Clear the Servlet spec's error attributes as {@link javax.servlet.http.HttpServletRequest}
	 * attributes under the keys defined in the Servlet 2.3 specification:
	 * {@code javax.servlet.error.status_code},
	 * {@code javax.servlet.error.exception_type},
	 * {@code javax.servlet.error.message},
	 * {@code javax.servlet.error.exception},
	 * {@code javax.servlet.error.request_uri},
	 * {@code javax.servlet.error.servlet_name}.
	 * @param request current servlet request
	 */
	public static void clearErrorRequestAttributes(HttpServletRequest request) {
		request.removeAttribute(ERROR_STATUS_CODE_ATTRIBUTE);
		request.removeAttribute(ERROR_EXCEPTION_TYPE_ATTRIBUTE);
		request.removeAttribute(ERROR_MESSAGE_ATTRIBUTE);
		request.removeAttribute(ERROR_EXCEPTION_ATTRIBUTE);
		request.removeAttribute(ERROR_REQUEST_URI_ATTRIBUTE);
		request.removeAttribute(ERROR_SERVLET_NAME_ATTRIBUTE);
	}

	Retrieve the first cookie with the given name. Note that multiple
cookies can have the same name but different paths or domains.
Params: request – current servlet request
name – cookie name
Returns: the first cookie with the given name, or null if none is found/**
	 * Retrieve the first cookie with the given name. Note that multiple
	 * cookies can have the same name but different paths or domains.
	 * @param request current servlet request
	 * @param name cookie name
	 * @return the first cookie with the given name, or {@code null} if none is found
	 */
	@Nullable
	public static Cookie getCookie(HttpServletRequest request, String name) {
		Assert.notNull(request, "Request must not be null");
		Cookie[] cookies = request.getCookies();
		if (cookies != null) {
			for (Cookie cookie : cookies) {
				if (name.equals(cookie.getName())) {
					return cookie;
				}
			}
		}
		return null;
	}

	Check if a specific input type="submit" parameter was sent in the request,
either via a button (directly with name) or via an image (name + ".x" or
name + ".y").
Params: request – current HTTP request
name – name of the parameter
See Also: SUBMIT_IMAGE_SUFFIXES
Returns: if the parameter was sent/**
	 * Check if a specific input type="submit" parameter was sent in the request,
	 * either via a button (directly with name) or via an image (name + ".x" or
	 * name + ".y").
	 * @param request current HTTP request
	 * @param name name of the parameter
	 * @return if the parameter was sent
	 * @see #SUBMIT_IMAGE_SUFFIXES
	 */
	public static boolean hasSubmitParameter(ServletRequest request, String name) {
		Assert.notNull(request, "Request must not be null");
		if (request.getParameter(name) != null) {
			return true;
		}
		for (String suffix : SUBMIT_IMAGE_SUFFIXES) {
			if (request.getParameter(name + suffix) != null) {
				return true;
			}
		}
		return false;
	}

	Obtain a named parameter from the given request parameters.
See findParameterValue(Map<String,?>, String) for a description of the lookup algorithm. 
Params: request – current HTTP request
name – the logical name of the request parameter
Returns: the value of the parameter, or null if the parameter does not exist in given request/**
	 * Obtain a named parameter from the given request parameters.
	 * <p>See {@link #findParameterValue(java.util.Map, String)}
	 * for a description of the lookup algorithm.
	 * @param request current HTTP request
	 * @param name the <i>logical</i> name of the request parameter
	 * @return the value of the parameter, or {@code null}
	 * if the parameter does not exist in given request
	 */
	@Nullable
	public static String findParameterValue(ServletRequest request, String name) {
		return findParameterValue(request.getParameterMap(), name);
	}

	Obtain a named parameter from the given request parameters.
This method will try to obtain a parameter value using the
following algorithm:

Try to get the parameter value using just the given logical name.
This handles parameters of the form logicalName = value. For normal
parameters, e.g. submitted using a hidden HTML form field, this will return
the requested value.
Try to obtain the parameter value from the parameter name, where the
parameter name in the request is of the form logicalName_value = xyz
with "_" being the configured delimiter. This deals with parameter values
submitted using an HTML form submit button.
If the value obtained in the previous step has a ".x" or ".y" suffix,
remove that. This handles cases where the value was submitted using an
HTML form image button. In this case the parameter in the request would
actually be of the form logicalName_value.x = 123. 

Params: parameters – the available parameter map
name – the logical name of the request parameter
Returns: the value of the parameter, or null if the parameter does not exist in given request/**
	 * Obtain a named parameter from the given request parameters.
	 * <p>This method will try to obtain a parameter value using the
	 * following algorithm:
	 * <ol>
	 * <li>Try to get the parameter value using just the given <i>logical</i> name.
	 * This handles parameters of the form <tt>logicalName = value</tt>. For normal
	 * parameters, e.g. submitted using a hidden HTML form field, this will return
	 * the requested value.</li>
	 * <li>Try to obtain the parameter value from the parameter name, where the
	 * parameter name in the request is of the form <tt>logicalName_value = xyz</tt>
	 * with "_" being the configured delimiter. This deals with parameter values
	 * submitted using an HTML form submit button.</li>
	 * <li>If the value obtained in the previous step has a ".x" or ".y" suffix,
	 * remove that. This handles cases where the value was submitted using an
	 * HTML form image button. In this case the parameter in the request would
	 * actually be of the form <tt>logicalName_value.x = 123</tt>. </li>
	 * </ol>
	 * @param parameters the available parameter map
	 * @param name the <i>logical</i> name of the request parameter
	 * @return the value of the parameter, or {@code null}
	 * if the parameter does not exist in given request
	 */
	@Nullable
	public static String findParameterValue(Map<String, ?> parameters, String name) {
		// First try to get it as a normal name=value parameter
		Object value = parameters.get(name);
		if (value instanceof String[]) {
			String[] values = (String[]) value;
			return (values.length > 0 ? values[0] : null);
		}
		else if (value != null) {
			return value.toString();
		}
		// If no value yet, try to get it as a name_value=xyz parameter
		String prefix = name + "_";
		for (String paramName : parameters.keySet()) {
			if (paramName.startsWith(prefix)) {
				// Support images buttons, which would submit parameters as name_value.x=123
				for (String suffix : SUBMIT_IMAGE_SUFFIXES) {
					if (paramName.endsWith(suffix)) {
						return paramName.substring(prefix.length(), paramName.length() - suffix.length());
					}
				}
				return paramName.substring(prefix.length());
			}
		}
		// We couldn't find the parameter value...
		return null;
	}

	Return a map containing all parameters with the given prefix.
Maps single values to String and multiple values to String array.
For example, with a prefix of "spring_", "spring_param1" and
"spring_param2" result in a Map with "param1" and "param2" as keys.
Params: request – the HTTP request in which to look for parameters
prefix – the beginning of parameter names
(if this is null or the empty string, all parameters will match)
See Also: ServletRequest.getParameterNames
ServletRequest.getParameterValues
ServletRequest.getParameterMap
Returns: map containing request parameters without the prefix,
containing either a String or a String array as values/**
	 * Return a map containing all parameters with the given prefix.
	 * Maps single values to String and multiple values to String array.
	 * <p>For example, with a prefix of "spring_", "spring_param1" and
	 * "spring_param2" result in a Map with "param1" and "param2" as keys.
	 * @param request the HTTP request in which to look for parameters
	 * @param prefix the beginning of parameter names
	 * (if this is null or the empty string, all parameters will match)
	 * @return map containing request parameters <b>without the prefix</b>,
	 * containing either a String or a String array as values
	 * @see javax.servlet.ServletRequest#getParameterNames
	 * @see javax.servlet.ServletRequest#getParameterValues
	 * @see javax.servlet.ServletRequest#getParameterMap
	 */
	public static Map<String, Object> getParametersStartingWith(ServletRequest request, @Nullable String prefix) {
		Assert.notNull(request, "Request must not be null");
		Enumeration<String> paramNames = request.getParameterNames();
		Map<String, Object> params = new TreeMap<>();
		if (prefix == null) {
			prefix = "";
		}
		while (paramNames != null && paramNames.hasMoreElements()) {
			String paramName = paramNames.nextElement();
			if ("".equals(prefix) || paramName.startsWith(prefix)) {
				String unprefixed = paramName.substring(prefix.length());
				String[] values = request.getParameterValues(paramName);
				if (values == null || values.length == 0) {
					// Do nothing, no values found at all.
				}
				else if (values.length > 1) {
					params.put(unprefixed, values);
				}
				else {
					params.put(unprefixed, values[0]);
				}
			}
		}
		return params;
	}

	Parse the given string with matrix variables. An example string would look like this "q1=a;q1=b;q2=a,b,c". The resulting map would contain keys "q1" and "q2" with values ["a","b"] and ["a","b","c"] respectively. 
Params: matrixVariables – the unparsed matrix variables string
Returns: a map with matrix variable names and values (never null)
Since: 3.2/**
	 * Parse the given string with matrix variables. An example string would look
	 * like this {@code "q1=a;q1=b;q2=a,b,c"}. The resulting map would contain
	 * keys {@code "q1"} and {@code "q2"} with values {@code ["a","b"]} and
	 * {@code ["a","b","c"]} respectively.
	 * @param matrixVariables the unparsed matrix variables string
	 * @return a map with matrix variable names and values (never {@code null})
	 * @since 3.2
	 */
	public static MultiValueMap<String, String> parseMatrixVariables(String matrixVariables) {
		MultiValueMap<String, String> result = new LinkedMultiValueMap<>();
		if (!StringUtils.hasText(matrixVariables)) {
			return result;
		}
		StringTokenizer pairs = new StringTokenizer(matrixVariables, ";");
		while (pairs.hasMoreTokens()) {
			String pair = pairs.nextToken();
			int index = pair.indexOf('=');
			if (index != -1) {
				String name = pair.substring(0, index);
				String rawValue = pair.substring(index + 1);
				for (String value : StringUtils.commaDelimitedListToStringArray(rawValue)) {
					result.add(name, value);
				}
			}
			else {
				result.add(pair, "");
			}
		}
		return result;
	}

	Check the given request origin against a list of allowed origins.
A list containing "*" means that all origins are allowed.
An empty list means only same origin is allowed.
Note: as of 5.1 this method ignores "Forwarded" and "X-Forwarded-*" headers that specify the client-originated address. Consider using the ForwardedHeaderFilter to extract and use, or to discard such headers. 
See Also: RFC 6454: The Web Origin Concept
Returns: true if the request origin is valid, false otherwise
Since: 4.1.5/**
	 * Check the given request origin against a list of allowed origins.
	 * A list containing "*" means that all origins are allowed.
	 * An empty list means only same origin is allowed.
	 *
	 * <p><strong>Note:</strong> as of 5.1 this method ignores
	 * {@code "Forwarded"} and {@code "X-Forwarded-*"} headers that specify the
	 * client-originated address. Consider using the {@code ForwardedHeaderFilter}
	 * to extract and use, or to discard such headers.
	 *
	 * @return {@code true} if the request origin is valid, {@code false} otherwise
	 * @since 4.1.5
	 * @see <a href="https://tools.ietf.org/html/rfc6454">RFC 6454: The Web Origin Concept</a>
	 */
	public static boolean isValidOrigin(HttpRequest request, Collection<String> allowedOrigins) {
		Assert.notNull(request, "Request must not be null");
		Assert.notNull(allowedOrigins, "Allowed origins must not be null");

		String origin = request.getHeaders().getOrigin();
		if (origin == null || allowedOrigins.contains("*")) {
			return true;
		}
		else if (CollectionUtils.isEmpty(allowedOrigins)) {
			return isSameOrigin(request);
		}
		else {
			return allowedOrigins.contains(origin);
		}
	}

	Check if the request is a same-origin one, based on Origin, Host, Forwarded, X-Forwarded-Proto, X-Forwarded-Host and X-Forwarded-Port headers. Note: as of 5.1 this method ignores "Forwarded" and "X-Forwarded-*" headers that specify the client-originated address. Consider using the ForwardedHeaderFilter to extract and use, or to discard such headers. 
Returns: true if the request is a same-origin one, false in case of cross-origin request
Since: 4.2/**
	 * Check if the request is a same-origin one, based on {@code Origin}, {@code Host},
	 * {@code Forwarded}, {@code X-Forwarded-Proto}, {@code X-Forwarded-Host} and
	 * {@code X-Forwarded-Port} headers.
	 *
	 * <p><strong>Note:</strong> as of 5.1 this method ignores
	 * {@code "Forwarded"} and {@code "X-Forwarded-*"} headers that specify the
	 * client-originated address. Consider using the {@code ForwardedHeaderFilter}
	 * to extract and use, or to discard such headers.

	 * @return {@code true} if the request is a same-origin one, {@code false} in case
	 * of cross-origin request
	 * @since 4.2
	 */
	public static boolean isSameOrigin(HttpRequest request) {
		HttpHeaders headers = request.getHeaders();
		String origin = headers.getOrigin();
		if (origin == null) {
			return true;
		}

		String scheme;
		String host;
		int port;
		if (request instanceof ServletServerHttpRequest) {
			// Build more efficiently if we can: we only need scheme, host, port for origin comparison
			HttpServletRequest servletRequest = ((ServletServerHttpRequest) request).getServletRequest();
			scheme = servletRequest.getScheme();
			host = servletRequest.getServerName();
			port = servletRequest.getServerPort();
		}
		else {
			URI uri = request.getURI();
			scheme = uri.getScheme();
			host = uri.getHost();
			port = uri.getPort();
		}

		UriComponents originUrl = UriComponentsBuilder.fromOriginHeader(origin).build();
		return (ObjectUtils.nullSafeEquals(scheme, originUrl.getScheme()) &&
				ObjectUtils.nullSafeEquals(host, originUrl.getHost()) &&
				getPort(scheme, port) == getPort(originUrl.getScheme(), originUrl.getPort()));
	}

	private static int getPort(@Nullable String scheme, int port) {
		if (port == -1) {
			if ("http".equals(scheme) || "ws".equals(scheme)) {
				port = 80;
			}
			else if ("https".equals(scheme) || "wss".equals(scheme)) {
				port = 443;
			}
		}
		return port;
	}

}
Params:	servletContext – the servlet context of the web application
Throws:	IllegalStateException – if the system property is already set, or if the WAR file is not expanded
See Also:	WEB_APP_ROOT_KEY_PARAM DEFAULT_WEB_APP_ROOT_KEY WebAppRootListener
Params:	servletContext – the servlet context of the web application
Returns:	whether default HTML escaping is enabled for the given application (`null` = no explicit default)
Params:	request – current HTTP request
Returns:	the session id, or `null` if none
Params:	request – current HTTP request name – the name of the session attribute
Returns:	the value of the session attribute, or `null` if not found
Params:	session – the HttpSession to find a mutex for
See Also:	SESSION_MUTEX_ATTRIBUTE HttpSessionMutexListener
Returns:	the mutex object (never `null`)
Params:	request – the servlet request to introspect requiredType – the desired type of request object
Returns:	the matching request object, or `null` if none of that type is available
Params:	response – the servlet response to introspect requiredType – the desired type of response object
Returns:	the matching response object, or `null` if none of that type is available
Params:	request – current servlet request
Returns:	whether the given request is an include request
Params:	request – current servlet request name – cookie name
Returns:	the first cookie with the given name, or `null` if none is found
Params:	request – current HTTP request name – name of the parameter
See Also:	SUBMIT_IMAGE_SUFFIXES
Returns:	if the parameter was sent
Params:	parameters – the available parameter map name – the logical name of the request parameter
Returns:	the value of the parameter, or `null` if the parameter does not exist in given request
Params:	request – the HTTP request in which to look for parameters prefix – the beginning of parameter names (if this is null or the empty string, all parameters will match)
See Also:	ServletRequest.getParameterNames ServletRequest.getParameterValues ServletRequest.getParameterMap
Returns:	map containing request parameters without the prefix, containing either a String or a String array as values
Params:	matrixVariables – the unparsed matrix variables string
Returns:	a map with matrix variable names and values (never `null`)
Since:	3.2
See Also:	RFC 6454: The Web Origin Concept
Returns:	`true` if the request origin is valid, `false` otherwise
Since:	4.1.5
Returns:	`true` if the request is a same-origin one, `false` in case of cross-origin request
Since:	4.2
/

org.springframework/ spring-web/ 5.1.5.RELEASE/ org/springframework/web/util/WebUtils.java
