CharacterEncodingFilter类的学习

web.xml内代码：

<!-- 字符集过滤器 -->  <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></span>

org.springframework.web.filter.CharacterEncodingFilter源码：

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;}@Overrideprotected 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);}}

CharacterEncodingFilter类可以通过简单配置来帮实现字符集转换的功能，参数encoding用于指定编码类型，参数forceEncoding设为true时，强制执行request.setCharacterEncoding(this.encoding)和reponse.setCharacterEncoding(this.encoding)中的方法。