Spring MVC Filter-Character set filter (Characterencodingfilter)

Spring's character set filtering is used to handle garbled problems in projects. The filter is located in the Org.springframework.web.filter package, pointing to the class Characterencodingfilter,characterencodingfilter source code as follows:

/*
 * Copyright 2002-2007 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.filter;

import java.io.IOException;
import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet 2.3/2.4 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 on Servlet 2.4+ containers (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 {

	private String encoding;

	private boolean forceEncoding = false;


	/**
	 * 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(String encoding) {
		this.encoding = 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>Note that the response encoding will only be set on Servlet 2.4+
	 * containers, since Servlet 2.3 did not provide a facility for setting
	 * a default response encoding.
	 */
	public void setForceEncoding(boolean forceEncoding) {
		this.forceEncoding = forceEncoding;
	}


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

		if (this.encoding != null && (this.forceEncoding || request.getCharacterEncoding() == null)) {
			request.setCharacterEncoding(this.encoding);
			if (this.forceEncoding) {
				response.setCharacterEncoding(this.encoding);
			}
		}
		filterChain.doFilter(request, response);
	}

}

The code above shows that you can set the value of two parameters when configuring a character set filter, as follows:

L Encoding: CharSet, the character set of the request to be filtered to encoding the specified value, such as UTF-8, is equivalent to:

Request.setcharacterencoding

L forceencoding: Literal meaning is mandatory character set, but you do not have to understand the literal meaning, because the value of this parameter is simply to specify whether the character set of the response is also encoding the specified set of characters, so you can choose to set to TRUE or false, When the value is true, the equivalent

Request.setcharacterencoding ("");
Response.setcharacterencoding ("");

When the value is false, it is equivalent to:

Request.setcharacterencoding ("");

The default value is False.

Example:

        <filter>
		<filter-name>characterEncodingFilter</filter-name>
		<filter-class> org.springframework.web.filter.characterencodingfilter</filter-class>
		<init-param>
			< param-name>encoding</param-name>
			<param-value>UTF-8</param-value>
		</init-param >
		<init-param>
			<param-name>forceEncoding</param-name>
			<param-value>true </param-value>
		</init-param>
	</filter>
	<filter-mapping>
		< Filter-name>characterencodingfilter</filter-name>
		<url-pattern>/*</url-pattern>
	</filter-mapping>

The above code is placed in Web. XML, equivalent to the servlet:

Request.setcharacterencoding ("UTF-8");
Response.setcharacterencoding ("UTF-8");