com.vilt.spring.context.response.OncePerRequestContextFilter.java Source code

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Here is the source code for com.vilt.spring.context.response.OncePerRequestContextFilter.java

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/*
 * Copyright 2002-2008 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 com.vilt.spring.context.response;

import static java.lang.Boolean.TRUE;

import java.io.IOException;

import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.web.filter.GenericFilterBean;

/**
 * Filter base class that guarantees to be just executed once per request, on
 * any servlet container. It provides a {@link #doFilterInternal} method with
 * HttpServletRequest and HttpServletResponse arguments.
 * 
 * <p>
 * The {@link #getAlreadyFilteredAttributeName} method determines how to
 * identify that a request is already filtered. The default implementation is
 * based on the configured name of the concrete filter instance.
 * 
 * @author Juergen Hoeller
 * @author Ricardo Santos
 * @since 27.03.2014
 */
public abstract class OncePerRequestContextFilter extends GenericFilterBean {

    /**
     * Suffix that gets appended to both the filter name and servlet context for
     * the "already filtered" request attribute.
     * 
     * @see #getAlreadyFilteredAttributeName
     */
    public static final String ALREADY_FILTERED_SUFFIX = ".FILTERED";

    /**
     * This <code>doFilter</code> implementation stores a request attribute for
     * "already filtered", proceeding without filtering again if the attribute
     * is already there.
     * 
     * @see #getAlreadyFilteredAttributeName
     * @see #doFilterInternal
     */
    public final void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain)
            throws ServletException, IOException {
        if (!(request instanceof HttpServletRequest) || !(response instanceof HttpServletResponse)) {
            throw new ServletException("OncePerRequestContextFilter just supports HTTP requests");
        }
        HttpServletRequest httpRequest = (HttpServletRequest) request;
        HttpServletResponse httpResponse = (HttpServletResponse) response;

        String alreadyFilteredAttributeName = getAlreadyFilteredAttributeName();
        if (request.getAttribute(alreadyFilteredAttributeName) != null) {
            // Proceed without invoking this filter...
            filterChain.doFilter(request, response);
            return;
        }
        // Do invoke this filter...
        request.setAttribute(alreadyFilteredAttributeName, TRUE);
        try {
            doFilterInternal(httpRequest, httpResponse, filterChain);
        } finally {
            // Remove the "already filtered" request attribute for this
            // request.
            request.removeAttribute(alreadyFilteredAttributeName);
        }
    }

    /**
     * Return the name of the request attribute that identifies that a request
     * is already filtered.
     * <p>
     * Default implementation appends the configured name of the concrete filter
     * instance, the configured servlet context name and "FILTERED" separated by
     * dots. If the filter is not fully initialized, it falls back to its class
     * name.
     * 
     * @see #getFilterName
     * @see #ALREADY_FILTERED_SUFFIX
     */
    protected String getAlreadyFilteredAttributeName() {
        String name = getFilterName();
        if (name == null) {
            name = getClass().getName();
        }
        return name + "." + getServletContext() + ALREADY_FILTERED_SUFFIX;
    }

    /**
     * Same contract as for <code>doFilter</code>, but guaranteed to be just
     * invoked once per request context. Provides HttpServletRequest and
     * HttpServletResponse arguments instead of the default ServletRequest and
     * ServletResponse ones.
     */
    protected abstract void doFilterInternal(HttpServletRequest request, HttpServletResponse response,
            FilterChain filterChain) throws ServletException, IOException;

}