过滤器filter一个小范例

WEB.XML
  <filter>
  <filter-name>infoFilter</filter-name>
  <filter-class>com.InfoFilter</filter-class>
  <init-param>
  <param-name>illegal</param-name>
  <param-value>cat,pig</param-value>
  </init-param>
</filter>

<filter-mapping>
<filter-name>infoFilter</filter-name>
<url-pattern>/Comment</url-pattern>
</filter-mapping> 


<servlet>
    <servlet-name>Comment</servlet-name>
    <servlet-class>com.Comment</servlet-class>
  </servlet>

  <servlet-mapping>
    <servlet-name>Comment</servlet-name>
    <url-pattern>/Comment</url-pattern>
  </servlet-mapping>
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>
----------------------------------------------------------------
public class Comment extends HttpServlet {


public void service(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
System.out.println("------service-----");
String addr =request.getRemoteAddr();
System.out.println(addr);

String info = request.getParameter("info");
System.out.println("servlet info:" + info);
response.setContentType("text/html");
PrintWriter out = response.getWriter();
out.println("<h1>info:"+ info + "</h1>");
}

-----------------------------------------------------------------


public class InfoFilter implements Filter {

private FilterConfig config;

/**
* web服务器删除Filter实例前，调用该方法
* 用于释放资源
*/
public void destroy() {
// TODO Auto-generated method stub

}

public void doFilter(ServletRequest arg0, ServletResponse arg1,
FilterChain arg2) throws IOException, ServletException {
System.out.println("--------Filter---------");
HttpServletRequest request = (HttpServletRequest)arg0;
HttpServletResponse response = (HttpServletResponse)arg1;
String info = request.getParameter("info");

System.out.println("filter info:" + info);
String illegalStr = config.getInitParameter("illegal");

String[] illegalStrs = illegalStr.split(",");
for (int i = 0; i < illegalStrs.length; i++) {
if(info.indexOf(illegalStrs[i])!= -1)
{
PrintWriter out = response.getWriter();
out.println("<h1>illegal info!</h1>");
return;
}
}

//将请求传给下一个组件（可能是一个Filter,也可能是一个servlet）
arg2.doFilter(arg0, arg1);

}

/**
* 用于初始化
* web服务器在实例化完成Filter之后，然后调用
* init()之前，实例化一个FilterConfig对象，然后在调用init()
* FilterConfig提供了方法，用来访问当前Filter的配置参数
*/
public void init(FilterConfig arg0) throws ServletException {
// TODO Auto-generated method stub

config = arg0;
}

}