CharacterEncodingFilter类的学习

web.xml内代码：

 <!-- 字符集过滤器 -->
  <filter>
    <filter-name>CharacterEncodingFilter</filter-name>
    <filter-class><span style="color:#ff0000;">org.springframework.web.filter.CharacterEncodingFilter</span></filter-class>
    <init-param>
      <param-name><span style="color:#ff0000;">encoding</span></param-name>
      <param-value>UTF-8</param-value>
    </init-param>
    <init-param>
      <param-name><span style="color:#ff0000;">forceEncoding</span></param-name>
      <param-value>true</param-value>
    </init-param>
  </filter>

<filter-mapping>
    <filter-name>CharacterEncodingFilter</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>

org.springframework.web.filter.CharacterEncodingFilter源码：

<span style="font-family: Arial, Helvetica, sans-serif;">package org.springframework.web.filter;</span>

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 <span style="color:#ff0000;">encoding</span>;

	private boolean <span style="color:#ff0000;">forceEncoding </span>= 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 (<span style="color:#ff0000;">this.encoding</span> != null && (<span style="color:#ff0000;">this.forceEncoding</span> || request.getCharacterEncoding() == null)) {
			<span style="color:#ff0000;">request.setCharacterEncoding(this.encoding);</span>
			if (this.forceEncoding) {
				<span style="color:#ff0000;">response.setCharacterEncoding(this.encoding);</span>
			}
		}
		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。