java中的拦截器和过滤器

拦截器与过滤器的区别 ： 
     1. 拦截器是基于java的反射机制的，而过滤器是基于函数回调。
     2. 拦截器不依赖与servlet容器，过滤器依赖与servlet容器。 
     3. 拦截器只能对action请求起作用，而过滤器则可以对几乎所有的请求起作用。
     4. 拦截器可以访问action上下文、值栈里的对象，而过滤器不能访问。 
     5. 在action的生命周期中，拦截器可以多次被调用，而过滤器只能在容器初始化时被调用一次

拦截器的代码实现(以struts2为例)：
1、在xml文件中如何定义拦截器
<interceptors>
 <interceptor name="filterIPInterceptor"
                         class="com.xxxx.web.FilterIPActionInterceptor" />
<interceptor-stack name="filterIPStack">
<interceptor-ref name="defaultStack" />
                              
<interceptor-ref name="filterIPInterceptor" />
</interceptor-stack>
</interceptors>
 
2、怎么遍别写自定义拦截器 
 
public class FilterIPActionInterceptor extends AbstractInterceptor
{
    /** 日志控制. */
    private final Log log = LogFactory.getLog(getClass());
 
    /**
     * @see com.opensymphony.xwork2.interceptor.AbstractInterceptor#intercept(com.opensymphony.xwork2.ActionInvocation)
     */
    @Override
    @SuppressWarnings("unchecked")
    public String intercept(ActionInvocation invocation) throws Exception
    {
        String result = null;
        // 获得当前方法名.
        String methodName = invocation.getInvocationContext().getName();
        String currIp = null;
        try
        {
            if (invocation.getAction() instanceof PortletAction)
            {
                PortletAction action = (PortletAction) invocation.getAction();
                currIp = action.getRequest().getRemoteAddr();
            }
            String ip = ApplicationResource.getHotValue("ALLOW_CACHE_IP");
 
            if (StringUtils.isBlank(ip) || StringUtils.isBlank(currIp))
            {
                log.error("允许刷新的IP不存在或当前请求的IP非法.");
                throw new NoAllowIPException();
            }
            else
            {
                String[] ips = ip.split(",");
                boolean errorIp = true;
                for (String s : ips)
                {
                    if (s.equals(currIp))
                        errorIp = false;
                }
                // 判断IP
                if (errorIp)
                    throw new NoAllowIPException();
            }
            result = invocation.invoke();//调用被拦截的方法
        }
        catch (Exception e)
        {
            log.error("异常类名:" + invocation.getAction().getClass());
            log.error("异常方法:" + methodName, e);
            throw e;
        }
 
        return result;
    }
 
}

3、怎么编写过滤器
 
     1、在web.xml里面配置自定义的拦截器
        <filter>
<filter-name>Redirect Filter</filter-name>
<filter-class>com.xx.filter.RedirectFilter</filter-class>
</filter>
 
<filter-mapping>
<filter-name>Redirect Filter</filter-name>
<url-pattern>/xx/xx/*</url-pattern>
 
</filter-mapping>
 
    2、如何编写自定义的拦截器
public class RedirectFilter implements Filter {
       public void doFilter(ServletRequest request, ServletResponse response,
              FilterChain filterChain) throws IOException, ServletException {
    // 获取URL
   Long startTime = null;
        if (log.isDebugEnabled())
        {
            startTime = System.currentTimeMillis();
        }
              HttpServletRequest httpRequest = (HttpServletRequest) request;
                          String url = httpRequest.getRequestURL().toString();
                      if (url == null || url.trim().length() == 0) {
                                    return;
                                                   }
                     if (url.indexOf(luceneCreateMapping) != -1
                                  || url.indexOf(luceneSearchMapping) != -1) {
                               doFilterForxxx(request, response, url);
                               } else {
                                     doxxxx(request, response, url);
                                    }
         if (log.isDebugEnabled())
        {
            long endTime = System.currentTimeMillis();
            Thread currentThread = Thread.currentThread();
            String threadName = currentThread.getName();
            log.debug("[" + threadName + "]" + "< "
                    + this.getClass().getName() + " " + url + " "
                    + (endTime - startTime) + " ms");
        }
// 激活下一个Filter
 filterChain.doFilter(request, response);
 
        }
}