弄過濾器，要實現filter接口
主要是用過濾器處理中文編碼，至于要用來做什么，再自己寫比如權限控制，登錄驗證，之類

//下面這是一個類。。。。
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.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class EncodingFilter implements Filter {
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws IOException, ServletException {
request.setCharacterEncoding("GBK");//處理編碼
response.setCharacterEncoding("GBK");//處理編碼

chain.doFilter(request, response);//讓過濾器執行下一個請求
}

public void destroy() {}

public void init(FilterConfig arg0) throws ServletException {}
}

//下面這個是在web.xml下的配置

<filter>
<filter-name>encoding</filter-name>
<filter-class>
剛剛創建的那個實現filter接口的類的位置
例如：com.temp.filter.EncodingFilter
</filter-class>
</filter>
<filter-mapping>
<filter-name>encoding</filter-name>
<url-pattern>*.jsp這個是以jsp為后綴的文件都攔截下來</url-pattern>
</filter-mapping>
可以寫多個的<filter-mapping>來配置你所要攔截的東西