tomcat中的一个过滤器例子

感谢：http://www.iteye.com/wiki/Struts/578-Struts原理与实践（5） 和Google

将所有的request的字符集也设置为UTF-8。虽然，我们可以在每个文件中加入这样的句子：request.setCharacterEncoding("UTF-8");来解决，但这样显得很麻烦。一种更简单的解决方法是使用filter。具体步骤如下： 

在mystruts\WEB-INF\classes目录下再新建一个名为filters的目录，新建一个名为：SetCharacterEncodingFilter的类，并保存在该目录下。其实，这个类并不要您亲自来写，可以借用tomcat中的例子。现将该例子的程序节选如下： 

package filters;
import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.UnavailableException;

public class SetCharacterEncodingFilter implements Filter {


 //可以理解为默认编码，在web.xml中配置后读取存入
    protected String encoding = null;


    protected FilterConfig filterConfig = null;

    protected boolean ignore = true;

    public void destroy() {

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

    }


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

        // Conditionally select and set the character encoding to be used
 //如果被忽略或者请求未设置编码，为了防止乱码，进行编码过滤
        if (ignore || (request.getCharacterEncoding() == null)) {
//设置请求编码为web.xml中配置的编码类型
            String encoding = selectEncoding(request);
            if (encoding != null)
                request.setCharacterEncoding(encoding);
        }

        // Pass control on to the next filter
 //由FilterChain进行过滤处理，而不是该Filter
        chain.doFilter(request, response);

    }

 //主要从配置文件中读取配置项并进行赋值
    public void init(FilterConfig filterConfig) throws ServletException {

        this.filterConfig = filterConfig;
  //从web.xml读取配置的编码，如gbk，utf－8等，赋值给encoding
        this.encoding = filterConfig.getInitParameter("encoding");
  //从web.xml读取是否忽略
        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 String selectEncoding(ServletRequest request) {

        return (this.encoding);

    }

}
<filter>
    <filter-name>Set Character Encoding</filter-name>
    <filter-class>filters.SetCharacterEncodingFilter</filter-class>
    <init-param>
      <param-name>encoding</param-name>
      <param-value>UTF-8</param-value>
    </init-param>
  </filter>
  <filter-mapping>
    <filter-name>Set Character Encoding</filter-name>
    <url-pattern>/*</url-pattern>
</filter-mapping>