加入拦截器后跳转到商店管理页面报空指针异常，拦截器实现与源码一致

java.lang.NullPointerException: null

at com.lin.o2o_2.interceptor.shopadmin.ShopLoginInterceptor.preHandle(ShopLoginInterceptor.java:23) ~[classes/:na]

at org.springframework.web.servlet.HandlerExecutionChain.applyPreHandle(HandlerExecutionChain.java:133) ~[spring-webmvc-4.3.12.RELEASE.jar:4.3.12.RELEASE]

at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:962) ~[spring-webmvc-4.3.12.RELEASE.jar:4.3.12.RELEASE]

at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:901) ~[spring-webmvc-4.3.12.RELEASE.jar:4.3.12.RELEASE]

at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970) ~[spring-webmvc-4.3.12.RELEASE.jar:4.3.12.RELEASE]

at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:861) ~[spring-webmvc-4.3.12.RELEASE.jar:4.3.12.RELEASE]

at javax.servlet.http.HttpServlet.service(HttpServlet.java:687) ~[javax.servlet-api-3.1.0.jar:3.1.0]

at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846) ~[spring-webmvc-4.3.12.RELEASE.jar:4.3.12.RELEASE]

at javax.servlet.http.HttpServlet.service(HttpServlet.java:790) ~[javax.servlet-api-3.1.0.jar:3.1.0]

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) ~[tomcat-embed-core-8.5.23.jar:8.5.23]

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.23.jar:8.5.23]

at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) ~[tomcat-embed-websocket-8.5.23.jar:8.5.23]

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.23.jar:8.5.23]

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.23.jar:8.5.23]

at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:197) ~[spring-web-4.3.12.RELEASE.jar:4.3.12.RELEASE]

at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-4.3.12.RELEASE.jar:4.3.12.RELEASE]

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.23.jar:8.5.23]

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.23.jar:8.5.23]

at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:199) ~[tomcat-embed-core-8.5.23.jar:8.5.23]

at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) ~[tomcat-embed-core-8.5.23.jar:8.5.23]

at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:478) ~[tomcat-embed-core-8.5.23.jar:8.5.23]

at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140) ~[tomcat-embed-core-8.5.23.jar:8.5.23]

at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81) ~[tomcat-embed-core-8.5.23.jar:8.5.23]

at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87) ~[tomcat-embed-core-8.5.23.jar:8.5.23]

at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342) ~[tomcat-embed-core-8.5.23.jar:8.5.23]

at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:803) ~[tomcat-embed-core-8.5.23.jar:8.5.23]

at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) ~[tomcat-embed-core-8.5.23.jar:8.5.23]

at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868) ~[tomcat-embed-core-8.5.23.jar:8.5.23]

at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1459) ~[tomcat-embed-core-8.5.23.jar:8.5.23]

at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) ~[tomcat-embed-core-8.5.23.jar:8.5.23]

at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) ~[na:na]

at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) ~[na:na]

at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) ~[tomcat-embed-core-8.5.23.jar:8.5.23]

at java.base/java.lang.Thread.run(Thread.java:834) ~[na:na]