请教书中例子一些技术性的问题

由于本人才疏学浅,可能提出的一些问题会贻笑大方,但还是希望能给出一些指点。

第4章cms例子的web.xml中有如下代码

<filter>
<filter-name>Set Character Encoding</filter-name>
<filter-class>com.jdon.util.SetCharacterEncodingFilter</filter-class>
<init-param>
<param-name>encoding</param-name>
<param-value>UTF-8</param-value>
</init-param>
<init-param>
<param-name>ignore</param-name>
<param-value>true</param-value>
</init-param>
</filter>
由于找不到这个类,是否可以将其完整删除?或者可以进行怎样的修改?
虽然不修改它也能够运行起来,我只是想知道正常情况(如果有它)会有和效果?

可以删除,网上也有类似源码,这是取自网上的源码,如下:



import javax.servlet.*;
import java.io.IOException;

/**
* <p>Filter that sets the character encoding to be used in parsing the
* incoming request, either unconditionally or only if the client did not
* specify a character encoding. Configuration of this filter is based on
* the following initialization parameters:</p>
* <ul>
* <li><strong>encoding</strong> - The character encoding to be configured
* for this request, either conditionally or unconditionally based on
* the <code>ignore</code> initialization parameter. This parameter
* is required, so there is no default.</li>
* <li><strong>ignore</strong> - If set to "true", any character encoding
* specified by the client is ignored, and the value returned by the
* <code>selectEncoding()</code> method is set. If set to "false,
* <code>selectEncoding()</code> is called <strong>only</strong> if the
* client has not already specified an encoding. By default, this
* parameter is set to "true".</li>
* </ul>
*
* <p>Although this filter can be used unchanged, it is also easy to
* subclass it and make the <code>selectEncoding()</code> method more
* intelligent about what encoding to choose, based on characteristics of
* the incoming request (such as the values of the <code>Accept-Language</code>
* and <code>User-Agent</code> headers, or a value stashed in the current
* user's session.</p>
*
* @author <a href="mailto:jwtronics@yahoo.com">John Wong</a>
*
* @version $Id: SetCharacterEncodingFilter.java,v 1.1 2002/04/10 13:59:27 johnwong Exp $
*/


public class SetCharacterEncodingFilter
implements Filter {

// ----------------------------------------------------- Instance Variables

/**
* The default character encoding to set for requests that pass through
* this filter.
*/

protected String encoding = null;

/**
* The filter configuration object we are associated with. If this value
* is null, this filter instance is not currently configured.
*/

protected FilterConfig filterConfig = null;

/**
* Should a character encoding specified by the client be ignored?
*/

protected boolean ignore = true;

// --------------------------------------------------------- Public Methods

/**
* Take this filter out of service.
*/

public void destroy() {

this.encoding = null;
this.filterConfig = null;

}

/**
* Select and set (if specified) the character encoding to be used to
* interpret request parameters for this request.
*
* @param request The servlet request we are processing
* @param result The servlet response we are creating
* @param chain The filter chain we are processing
*
* @exception IOException if an input/output error occurs
* @exception ServletException if a servlet error occurs
*/

public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws IOException, ServletException {

// Conditionally select and set the character encoding to be used
if (ignore || (request.getCharacterEncoding() == null)) {
String encoding = selectEncoding(request);
if (encoding != null)
request.setCharacterEncoding(encoding);
}

// Pass control on to the next filter
chain.doFilter(request, response);

}

/**
* Place this filter into service.
*
* @param filterConfig The filter configuration object
*/

public void init(FilterConfig filterConfig) throws ServletException {

this.filterConfig = filterConfig;
this.encoding = filterConfig.getInitParameter(
"encoding");
PropsUtil.ENCODING = this.encoding;
String value = filterConfig.getInitParameter(
"ignore");
if (value == null)
this.ignore = true;
else if (value.equalsIgnoreCase(
"true"))
this.ignore = true;
else if (value.equalsIgnoreCase(
"yes"))
this.ignore = true;
else
this.ignore = false;

}

// ------------------------------------------------------ Protected Methods

/**
* Select an appropriate character encoding to be used, based on the
* characteristics of the current request and/or filter initialization
* parameters. If no character encoding should be set, return
* <code>null</code>.
* <p>
* The default implementation unconditionally returns the value configured
* by the <strong>encoding</strong> initialization parameter for this
* filter.
*
* @param request The servlet request we are processing
*/

protected String selectEncoding(ServletRequest request) {

return (this.encoding);

}

}