org.jruby.rack.mock.WebUtils.java Source code

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/*
 * Copyright 2002-2014 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.jruby.rack.mock;

import java.io.File;
import java.io.FileNotFoundException;
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.util.Assert;
import org.springframework.util.LinkedMultiValueMap;
import org.springframework.util.MultiValueMap;
import org.springframework.util.StringUtils;

/**
 * Miscellaneous utilities for web applications.
 * Used by various framework classes.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 */
abstract class WebUtils {

    /**
     * Standard Servlet 2.3+ spec request attributes for include URI and paths.
     * <p>If included via a RequestDispatcher, the current resource will see the
     * originating request. Its own URI and paths are exposed as request attributes.
     */
    public static final String INCLUDE_REQUEST_URI_ATTRIBUTE = "javax.servlet.include.request_uri";
    public static final String INCLUDE_CONTEXT_PATH_ATTRIBUTE = "javax.servlet.include.context_path";
    public static final String INCLUDE_SERVLET_PATH_ATTRIBUTE = "javax.servlet.include.servlet_path";
    public static final String INCLUDE_PATH_INFO_ATTRIBUTE = "javax.servlet.include.path_info";
    public static final String INCLUDE_QUERY_STRING_ATTRIBUTE = "javax.servlet.include.query_string";

    /**
     * Standard Servlet 2.4+ spec request attributes for forward URI and paths.
     * <p>If forwarded to via a RequestDispatcher, the current resource will see its
     * own URI and paths. The originating URI and paths are exposed as request attributes.
     */
    public static final String FORWARD_REQUEST_URI_ATTRIBUTE = "javax.servlet.forward.request_uri";
    public static final String FORWARD_CONTEXT_PATH_ATTRIBUTE = "javax.servlet.forward.context_path";
    public static final String FORWARD_SERVLET_PATH_ATTRIBUTE = "javax.servlet.forward.servlet_path";
    public static final String FORWARD_PATH_INFO_ATTRIBUTE = "javax.servlet.forward.path_info";
    public static final String FORWARD_QUERY_STRING_ATTRIBUTE = "javax.servlet.forward.query_string";

    /**
     * Standard Servlet 2.3+ spec request attributes for error pages.
     * <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";
    public static final String ERROR_EXCEPTION_TYPE_ATTRIBUTE = "javax.servlet.error.exception_type";
    public static final String ERROR_MESSAGE_ATTRIBUTE = "javax.servlet.error.message";
    public static final String ERROR_EXCEPTION_ATTRIBUTE = "javax.servlet.error.exception";
    public static final String ERROR_REQUEST_URI_ATTRIBUTE = "javax.servlet.error.request_uri";
    public static final String ERROR_SERVLET_NAME_ATTRIBUTE = "javax.servlet.error.servlet_name";

    /**
     * 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 {@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 {@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 {@code web.xml}): "defaultHtmlEscape".
     */
    public static final String HTML_ESCAPE_CONTEXT_PARAM = "defaultHtmlEscape";

    /**
     * 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" */
    public static final String DEFAULT_WEB_APP_ROOT_KEY = "webapp.root";

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

    /** 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 {@code web.xml}. Default is "webapp.root".
     * <p>Can be used for tools that support substition 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
     * @see Log4jWebConfigurer
     */
    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.
     * @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 {@code web.xml}
     * (if any). Falls back to {@code false} in case of no explicit default given.
     * @param servletContext the servlet context of the web application
     * @return whether default HTML escaping is enabled (default is false)
     */
    public static boolean isDefaultHtmlEscape(ServletContext servletContext) {
        if (servletContext == null) {
            return false;
        }
        String param = servletContext.getInitParameter(HTML_ESCAPE_CONTEXT_PARAM);
        return Boolean.valueOf(param);
    }

    /**
     * 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 (null = no explicit default)
     */
    public static Boolean getDefaultHtmlEscape(ServletContext servletContext) {
        if (servletContext == null) {
            return null;
        }
        String param = servletContext.getInitParameter(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.
     * @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.
     * <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.
     * @param request current HTTP request
     * @return the session id, or {@code null} if none
     */
    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!
     * @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
     */
    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!
     * @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!
     * @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, 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);
            }
        }
    }

    /**
     * Get the specified session attribute, creating and setting a new attribute if
     * no existing found. The given class needs to have a public no-arg constructor.
     * Useful for on-demand state objects in a web tier, like shopping carts.
     * @param session current HTTP session
     * @param name the name of the session attribute
     * @param clazz the class to instantiate for a new attribute
     * @return the value of the session attribute, newly created if not found
     * @throws IllegalArgumentException if the session attribute could not be instantiated
     */
    public static Object getOrCreateSessionAttribute(HttpSession session, String name, Class<?> clazz)
            throws IllegalArgumentException {

        Assert.notNull(session, "Session must not be null");
        Object sessionObject = session.getAttribute(name);
        if (sessionObject == null) {
            try {
                sessionObject = clazz.newInstance();
            } catch (InstantiationException ex) {
                throw new IllegalArgumentException("Could not instantiate class [" + clazz.getName()
                        + "] for session attribute '" + name + "': " + ex.getMessage());
            } catch (IllegalAccessException ex) {
                throw new IllegalArgumentException("Could not access default constructor of class ["
                        + clazz.getName() + "] for session attribute '" + name + "': " + ex.getMessage());
            }
            session.setAttribute(name, sessionObject);
        }
        return sessionObject;
    }

    /**
     * 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.
     * @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")
    public static <T> T getNativeRequest(ServletRequest request, 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.
     * @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")
    public static <T> T getNativeResponse(ServletResponse response, 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.
     * <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 {@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, 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());
        exposeRequestAttributeIfNotPresent(request, ERROR_SERVLET_NAME_ATTRIBUTE, servletName);
    }

    /**
     * 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 {@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);
    }

    /**
     * Expose the given Map as request attributes, using the keys as attribute names
     * and the values as corresponding attribute values. Keys need to be Strings.
     * @param request current HTTP request
     * @param attributes the attributes Map
     */
    public static void exposeRequestAttributes(ServletRequest request, Map<String, ?> attributes) {
        Assert.notNull(request, "Request must not be null");
        Assert.notNull(attributes, "Attributes Map must not be null");
        for (Map.Entry<String, ?> entry : attributes.entrySet()) {
            request.setAttribute(entry.getKey(), entry.getValue());
        }
    }

    /**
     * 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
     */
    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").
     * @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.
     * <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
     */
    public static String findParameterValue(ServletRequest request, String name) {
        return findParameterValue(request.getParameterMap(), name);
    }

    /**
     * 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
     */
    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.
     * <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 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, String prefix) {
        Assert.notNull(request, "Request must not be null");
        Enumeration<String> paramNames = request.getParameterNames();
        Map<String, Object> params = new TreeMap<String, Object>();
        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;
    }

    /**
     * Return the target page specified in the request.
     * @param request current servlet request
     * @param paramPrefix the parameter prefix to check for
     * (e.g. "_target" for parameters like "_target1" or "_target2")
     * @param currentPage the current page, to be returned as fallback
     * if no target page specified
     * @return the page specified in the request, or current page if not found
     */
    public static int getTargetPage(ServletRequest request, String paramPrefix, int currentPage) {
        Enumeration<String> paramNames = request.getParameterNames();
        while (paramNames.hasMoreElements()) {
            String paramName = paramNames.nextElement();
            if (paramName.startsWith(paramPrefix)) {
                for (int i = 0; i < WebUtils.SUBMIT_IMAGE_SUFFIXES.length; i++) {
                    String suffix = WebUtils.SUBMIT_IMAGE_SUFFIXES[i];
                    if (paramName.endsWith(suffix)) {
                        paramName = paramName.substring(0, paramName.length() - suffix.length());
                    }
                }
                return Integer.parseInt(paramName.substring(paramPrefix.length()));
            }
        }
        return currentPage;
    }

    /**
     * Extract the URL filename from the given request URL path.
     * Correctly resolves nested paths such as "/products/view.html" as well.
     * @param urlPath the request URL path (e.g. "/index.html")
     * @return the extracted URI filename (e.g. "index")
     */
    public static String extractFilenameFromUrlPath(String urlPath) {
        String filename = extractFullFilenameFromUrlPath(urlPath);
        int dotIndex = filename.lastIndexOf('.');
        if (dotIndex != -1) {
            filename = filename.substring(0, dotIndex);
        }
        return filename;
    }

    /**
     * Extract the full URL filename (including file extension) from the given request URL path.
     * Correctly resolves nested paths such as "/products/view.html" as well.
     * @param urlPath the request URL path (e.g. "/products/index.html")
     * @return the extracted URI filename (e.g. "index.html")
     */
    public static String extractFullFilenameFromUrlPath(String urlPath) {
        int end = urlPath.indexOf(';');
        if (end == -1) {
            end = urlPath.indexOf('?');
            if (end == -1) {
                end = urlPath.length();
            }
        }
        int begin = urlPath.lastIndexOf('/', end) + 1;
        return urlPath.substring(begin, end);
    }

    /**
     * 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}
     */
    public static MultiValueMap<String, String> parseMatrixVariables(String matrixVariables) {
        MultiValueMap<String, String> result = new LinkedMultiValueMap<String, String>();
        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;
    }
}