/*
 * 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
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.filter;

import java.io.IOException;

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

import org.springframework.lang.Nullable;
import org.springframework.util.Assert;

/**
 * Servlet Filter that allows one to specify a character encoding for requests.
 * This is useful because current browsers typically do not set a character
 * encoding even if specified in the HTML page or form.
 *
 * <p>This filter can either apply its encoding if the request does not already
 * specify an encoding, or enforce this filter's encoding in any case
 * ("forceEncoding"="true"). In the latter case, the encoding will also be
 * applied as default response encoding (although this will usually be overridden
 * by a full content type set in the view).
 *
 * @author Juergen Hoeller
 * @since 15.03.2004
 * @see #setEncoding
 * @see #setForceEncoding
 * @see javax.servlet.http.HttpServletRequest#setCharacterEncoding
 * @see javax.servlet.http.HttpServletResponse#setCharacterEncoding
 */
public class CharacterEncodingFilter extends OncePerRequestFilter {

        @Nullable
        private String encoding;

        private boolean forceRequestEncoding = false;

        private boolean forceResponseEncoding = false;


        /**
         * Create a default {@code CharacterEncodingFilter},
         * with the encoding to be set via {@link #setEncoding}.
         * @see #setEncoding
         */
        public CharacterEncodingFilter() {
        }

        /**
         * Create a {@code CharacterEncodingFilter} for the given encoding.
         * @param encoding the encoding to apply
         * @since 4.2.3
         * @see #setEncoding
         */
        public CharacterEncodingFilter(String encoding) {
                this(encoding, false);
        }

        /**
         * Create a {@code CharacterEncodingFilter} for the given encoding.
         * @param encoding the encoding to apply
         * @param forceEncoding whether the specified encoding is supposed to
         * override existing request and response encodings
         * @since 4.2.3
         * @see #setEncoding
         * @see #setForceEncoding
         */
        public CharacterEncodingFilter(String encoding, boolean forceEncoding) {
                this(encoding, forceEncoding, forceEncoding);
        }

        /**
         * Create a {@code CharacterEncodingFilter} for the given encoding.
         * @param encoding the encoding to apply
         * @param forceRequestEncoding whether the specified encoding is supposed to
         * override existing request encodings
         * @param forceResponseEncoding whether the specified encoding is supposed to
         * override existing response encodings
         * @since 4.3
         * @see #setEncoding
         * @see #setForceRequestEncoding(boolean)
         * @see #setForceResponseEncoding(boolean)
         */
        public CharacterEncodingFilter(String encoding, boolean forceRequestEncoding, boolean forceResponseEncoding) {
                Assert.hasLength(encoding, "Encoding must not be empty");
                this.encoding = encoding;
                this.forceRequestEncoding = forceRequestEncoding;
                this.forceResponseEncoding = forceResponseEncoding;
        }


        /**
         * Set the encoding to use for requests. This encoding will be passed into a
         * {@link javax.servlet.http.HttpServletRequest#setCharacterEncoding} call.
         * <p>Whether this encoding will override existing request encodings
         * (and whether it will be applied as default response encoding as well)
         * depends on the {@link #setForceEncoding "forceEncoding"} flag.
         */
        public void setEncoding(@Nullable String encoding) {
                this.encoding = encoding;
        }

        /**
         * Return the configured encoding for requests and/or responses.
         * @since 4.3
         */
        @Nullable
        public String getEncoding() {
                return this.encoding;
        }

        /**
         * Set whether the configured {@link #setEncoding encoding} of this filter
         * is supposed to override existing request and response encodings.
         * <p>Default is "false", i.e. do not modify the encoding if
         * {@link javax.servlet.http.HttpServletRequest#getCharacterEncoding()}
         * returns a non-null value. Switch this to "true" to enforce the specified
         * encoding in any case, applying it as default response encoding as well.
         * <p>This is the equivalent to setting both {@link #setForceRequestEncoding(boolean)}
         * and {@link #setForceResponseEncoding(boolean)}.
         * @see #setForceRequestEncoding(boolean)
         * @see #setForceResponseEncoding(boolean)
         */
        public void setForceEncoding(boolean forceEncoding) {
                this.forceRequestEncoding = forceEncoding;
                this.forceResponseEncoding = forceEncoding;
        }

        /**
         * Set whether the configured {@link #setEncoding encoding} of this filter
         * is supposed to override existing request encodings.
         * <p>Default is "false", i.e. do not modify the encoding if
         * {@link javax.servlet.http.HttpServletRequest#getCharacterEncoding()}
         * returns a non-null value. Switch this to "true" to enforce the specified
         * encoding in any case.
         * @since 4.3
         */
        public void setForceRequestEncoding(boolean forceRequestEncoding) {
                this.forceRequestEncoding = forceRequestEncoding;
        }

        /**
         * Return whether the encoding should be forced on requests.
         * @since 4.3
         */
        public boolean isForceRequestEncoding() {
                return this.forceRequestEncoding;
        }

        /**
         * Set whether the configured {@link #setEncoding encoding} of this filter
         * is supposed to override existing response encodings.
         * <p>Default is "false", i.e. do not modify the encoding.
         * Switch this to "true" to enforce the specified encoding
         * for responses in any case.
         * @since 4.3
         */
        public void setForceResponseEncoding(boolean forceResponseEncoding) {
                this.forceResponseEncoding = forceResponseEncoding;
        }

        /**
         * Return whether the encoding should be forced on responses.
         * @since 4.3
         */
        public boolean isForceResponseEncoding() {
                return this.forceResponseEncoding;
        }


        @Override
        protected void doFilterInternal(
                        HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)
                        throws ServletException, IOException {

                String encoding = getEncoding();
                if (encoding != null) {
                        if (isForceRequestEncoding() || request.getCharacterEncoding() == null) {
                                request.setCharacterEncoding(encoding);
                        }
                        if (isForceResponseEncoding()) {
                                response.setCharacterEncoding(encoding);
                        }
                }
                filterChain.doFilter(request, response);
        }

}