面试又问：拦截器和过滤器的区别！

@Override
public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception
{
    // 在拦截点（Controller方法处理之前）执行拦截 若返回的是false则中断执行 反之亦然
    return false;
}

@Override
public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception
{
    // 在处理过程中（Controller方法处理完之后  DispatcherServlet进行视图的渲染之前）执行拦截
}

@Override
public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception
{
    // 在DispatcherServlet进行视图的渲染后 返回前进行拦截
}

@Override
public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception
 {
     // 在Controller方法处理之前执行拦截 若返回的是false则中断执行 反之亦然

     // 判断当前的User是否为空 若不为空则不拦截
     if (request.getSession().getAttribute("USERINFO")!=null)
     {
         return true;
     }
     // 进行拦截 返回登录界面
     response.sendRedirect(request.getContextPath()+"/user/doLogin.do");
     return false;
 }

<!-- 配置拦截器 -->
<mvc:interceptors>
    <mvc:interceptor>
        <!-- 拦截所有的mvc控制器(Controller) -->
        <mvc:mapping path="/**"/>
        <!-- 放行机制 指定对某个页面不进行拦截 -->
        <!-- 拦截器只对action起作用 因此填入的不是页面路径 而是方法 -->
        <mvc:exclude-mapping path="/user/doLogin.do"/>
        <!-- 指定使用哪个拦截器 -->
        <bean class="net.zjitc.interceptor.LoginInterceptor"/>
    </mvc:interceptor>
</mvc:interceptors>

public class LoginFilter implements Filter {

    @Override
    public void init(FilterConfig filterConfig) throws ServletException
    {
        // 过滤器初始化
    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException
    {

    }

    @Override
    public void destroy()
    {
        // 过滤器销毁
    }
}

@Override
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException
{
    // ServletRequest是一个接口 而HttpServletRequest是接口的实现
    // 但有些方法是HttpServletRequest独有的 例如getSession()
    // HttpServletRequest接口继承自ServletRequest接口 增加了和Http相关的方法
    // 但是我们可以强制转换
    HttpServletRequest request=(HttpServletRequest)servletRequest;
    HttpServletResponse response=(HttpServletResponse)servletResponse;

    // 若用户没有登录
    if (request.getSession().getAttribute("USERINFO")==null && request.getRequestURI().indexOf("/user/doLogin.do")==-1)
    {
        response.sendRedirect(request.getContextPath()+"/user/doLogin.do");
    }
    // 若用户已经登录 则继续下一个请求(继续访问)
    filterChain.doFilter(request,response);
}

<!-- 配置自定义的Filter 实现登录控制 -->
 <filter>
     <filter-name>sessionFilter</filter-name>
     <filter-class>net.zjitc.filter.LoginFilter</filter-class>
 </filter>
 <filter-mapping>
     <filter-name>sessionFilter</filter-name>
     <!-- 拦截所有的页面 /斜杠代表在webapp目录下 -->
     <url-pattern>/pages/*</url-pattern>
     <url-pattern>/css/*</url-pattern>
     <url-pattern>/img/*</url-pattern>
     <url-pattern>/failer.jsp</url-pattern>
 </filter-mapping>

destory()
doFilter(ServletRequest request,ServletResponse response,FilterCjain chain)
init(FilterConfig filterConfig)