Filter

web.xml文件
<filter>
<filter-name></filter-name>
<filter-class></filter-class>
</filter>
<filter-mapping>
<filter-name> </filter-name>
<url-pattern>/*</url-pattern><!--/*指所有的请求都可以-->
</filter-mapping>

实现类.Class    继承Filter
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException
    {
        // TODO Auto-generated method stub
        System.out.println("doFilter-------------------");
        //检查放行
        chain.doFilter( request, response);
    }

实现类.Class    
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException
    {
        // TODO Auto-generated method stub
        System.out.println("doFilter-------------------");
        //凡是经过Filter的字符格式都为UTF-8
        HttpServletRequest req=(HttpServletRequest)request;
        req.setCharacterEncoding("UTF-8");
        //检查放行
        chain.doFilter( request, response);
    }