过滤器，拦截器，监听器具体应用上的区别

过滤器filter

过滤掉非法url（不是login.do的地址请求，如果用户没有登陆都过滤掉）,或者在传入servlet或者 struts的action前统一设置字符集， 或者去除掉一些非法字符（聊天室经常用到的，一些骂人的话）。

最常用的过滤器就是登陆过滤器LoginFilter，过滤器一般都是继承Filter 接口

public class LoginFilter extends HttpServlet implements Filter {

@Override
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws IOException, ServletException {
HttpServletRequest req = (HttpServletRequest) request;
HttpServletResponse res = (HttpServletResponse) response;
HttpSession session = req.getSession();
if(session.getAttribute("").equals("")){

}
String url = req.getServletPath();
String contextPath = req.getContextPath();
res.sendRedirect(contextPath + "/jspPage/login.jsp");
}

@Override
public void init(FilterConfig arg0) throws ServletException {
// TODO Auto-generated method stub

}

拦截器interceptor:

进行权限验证，或者是来判断用户是否登陆，日志记录，或者限制时间点访问。我自己用过拦截器，是用户每次登录时，都能记录一个登录时间。 （这点用拦截器明显合适，用过滤器明显不合适，因为没有过滤任何东西）

public class EntranceInterceptor extends HandlerInterceptorAdapter {

private Logger LOG = Logger.getLogger(EntranceInterceptor.class);

@Override
public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {

MDC.put(LogUtil.KEY_REQUEST_ID, RandomStringUtils.randomAlphanumeric(8));
LOG.debug(LogUtil.getLogStr(request));

//过滤掉静态资源
if(handler instanceof HandlerMethod){

//获取游戏
String url = request.getRequestURI();
if(!"".equals(url) && !"/".equals(url)){
String str = url.substring(url.indexOf("/") + 1);
StringTokenizer st = new StringTokenizer(str, "/");

String game = "";
int c = 0;
while (st.hasMoreTokens()) {
if(++c == 2){
game = st.nextToken();
}
st.nextToken();
}
LOG.debug(LogUtil.getLogStr("[当前访问活动名称]:[" + game + "]"));
TempleConfigContext.setCurrentGameActivity(GameActivityEnum.getGameActivityEnum(game));
}

//是否有AjaxAnno注解
HandlerMethod method = (HandlerMethod) handler;
AjaxAnno anno = method.getBean().getClass().getAnnotation(AjaxAnno.class);
if (anno != null || (anno = method.getMethod().getAnnotation(AjaxAnno.class)) != null) {
TempleConfigContext.setCurrentRequestType(TempleConfigContext.AJAX_REQUEST_TYPE);
}

LoginRequired required = method.getBean().getClass().getAnnotation(LoginRequired.class);
if (required !=
4000
null || (required = method.getMethod().getAnnotation(LoginRequired.class)) != null) {
//验证是否登录
GameActivityEnum activity = TempleConfigContext.getCurrentGameActivity();
if (request.getSession().getAttribute(activity.getActivity() + "_" + Constant.MANAGER_SESSION_LOGIN_USER) == null) {// 判断session里是否有用户信息
throw new BusinessException(CommonStateEnum.BADREQ_PARA_SESSION_TIMEOUT, "您还没有登录或者您的登录已经过期");
}
}

PassAction pass = method.getBean().getClass().getAnnotation(PassAction.class);
if (pass == null && (pass = method.getMethod().getAnnotation(PassAction.class)) == null) {
//验证是否过期
Date[] limit = Constant.getHdLimitTime(TempleConfigContext.getCurrentGameActivity().getActivity());
if(null != limit){
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
Date date = new Date();
if(null != limit[0] && date.before(limit[0])){
CommonStateEnum error = CommonStateEnum.BADREQ_API_HD_NOT_SATRT;
throw new BusinessException(error, error.getMessage(sdf.format(limit[0])));
}

if(null != limit[1] && date.after(limit[1])){
CommonStateEnum error = CommonStateEnum.BADREQ_API_HD_ALREADY_END;
throw new BusinessException(error, error.getMessage(sdf.format(limit[0]), sdf.format(limit[1])));
}
}
}
}

return true;
}

@Override
public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {

}

@Override
public void afterCompletion(HttpServletRequest request,
HttpServletResponse response, Object handler, Exception ex)
throws Exception {
MDC.remove(LogUtil.KEY_REQUEST_ID);
}
}

监听器listener

当你要触发一个事件，但这件事既不是过滤，又不是拦截，那很可能就是监听！ 联想到Windows编程里的，单击鼠标、改变窗口尺寸、按下键盘上的一个键都会使Windows发送一个消息给应用程序。监听器的概念类似于这些。

public final class Log4jConfigListener implements ServletContextListener {
/**
* 配置文件位置
*/
public final String CONFIG_LOCATION_PARAM = "log4jConfigLocation";
/**
* 日志文件存放位置
*/
public final String LOG_DIR = "logDir";
/**
* root log 记录级别
*/
public final String ROOT_LOG_LEVEL = "rootLogLevel";

public final String CONSOLE_LOGGIN_LEVEL = "consoleLogginLevel";

@Override
public void contextInitialized(ServletContextEvent sce) {
final ServletContext context = sce.getServletContext();
initProperty(context);
String location = context.getInitParameter(CONFIG_LOCATION_PARAM);
location = getRealPath(context, location);
initLogging(location);
}

@Override
public void contextDestroyed(ServletContextEvent sce) {
LogManager.shutdown();
}

public String getRealPath(ServletContext servletContext, String path) {
if (!path.startsWith("/")) {
path = "/" + path;
}
String realPath = servletContext.getRealPath(path);
if (realPath == null) {
throw new RuntimeException(
"ServletContext resource [" + path + "] cannot be resolved to absolute file path - " +
"web application archive not expanded?");
}
return realPath;
}

public void initProperty(ServletContext context) {
String logDir = context.getInitParameter(LOG_DIR);
String rootLogLevel = context.getInitParameter(ROOT_LOG_LEVEL);
String consoleLogginLevel = context.getInitParameter(CONSOLE_LOGGIN_LEVEL);
if (logDir == null || logDir.startsWith("${") || (System.getProperty("os.name").startsWith("Windows") && logDir.startsWith("/")))
logDir = System.getProperty("user.home") + "/logs/";
System.setProperty("LOG_DIR", logDir);
if (rootLogLevel == null || rootLogLevel.startsWith("${")) {
rootLogLevel = "INFO";
}
System.setProperty("ROOT_LOG_LEVEL", rootLogLevel);
if (consoleLogginLevel == null || consoleLogginLevel.startsWith("${")) {
consoleLogginLevel = "INFO";
}
System.setProperty("CONSOLE_LOGGIN_LEVEL", consoleLogginLevel);
}

public void initLogging(String location) {
if (location.toLowerCase().endsWith(".xml")) {
DOMConfigurator.configure(location);
} else {
PropertyConfigurator.configure(location);
}
}

这些例子都是引用了spring MVC框架中的类