在我当前的spring项目中，我有一个此类，该类应为来自不同控制器的多个视图提供一些modelAttributes：
@ControllerAdvice
public class Model {
@Autowired
private CategoriaService categoria;
@Autowired
private ProdutoService produto;
@Autowired
private UsuarioService usuario;
@Autowired
private CredencialService credencial;
@ModelAttribute("categorias")
public List<Categoria> categorias() {
return categoria.select();
}
@ModelAttribute("produtos")
public List<Produto> produtos() {
return produto.select();
}
@ModelAttribute("usuario")
public Usuario usuario() {
return usuario.findBy("username", SecurityContextHolder.getContext().getAuthentication().getName());
}
@ModelAttribute("credenciais")
public List<Credencial> credenciais() {
return credencial.select();
}
}
现在，我的视图分布在2个类中：
@Controller
public class Home {
...
}
具有公共页面的视图，例如/，/signin和/signup。并且：
public abstract class Controller<E> {
private Class<E> clazz;
@Autowired
protected Service<E> serv;
public Controller(Class<E> clazz) {
this.clazz = clazz;
}
...
}
泛型类，它定义到模型层类上的操作的映射，例如插入，更新和删除。一些模型类使用它们自己的映射来扩展该类。
现在，当我尝试访问某些扩展方法（使用XMLHttpRequest）时，出现此错误：
java.lang.NullPointerException: null
at org.loja.Model.usuario(Model.java:43) ~[classes/:1.0-SNAPSHOT]
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:na]
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:na]
at java.base/java.lang.reflect.Method.invoke(Method.java:566) ~[na:na]
at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:209) ~[spring-web-5.0.9.RELEASE.jar:5.0.9.RELEASE]
at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:136) ~[spring-web-5.0.9.RELEASE.jar:5.0.9.RELEASE]
at org.springframework.web.method.annotation.ModelFactory.invokeModelAttributeMethods(ModelFactory.java:142) ~[spring-web-5.0.9.RELEASE.jar:5.0.9.RELEASE]
at org.springframework.web.method.annotation.ModelFactory.initModel(ModelFactory.java:111) ~[spring-web-5.0.9.RELEASE.jar:5.0.9.RELEASE]
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:869) ~[spring-webmvc-5.0.9.RELEASE.jar:5.0.9.RELEASE]
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:797) ~[spring-webmvc-5.0.9.RELEASE.jar:5.0.9.RELEASE]
at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.0.9.RELEASE.jar:5.0.9.RELEASE]
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:991) ~[spring-webmvc-5.0.9.RELEASE.jar:5.0.9.RELEASE]
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:925) ~[spring-webmvc-5.0.9.RELEASE.jar:5.0.9.RELEASE]
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:974) ~[spring-webmvc-5.0.9.RELEASE.jar:5.0.9.RELEASE]
at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:877) ~[spring-webmvc-5.0.9.RELEASE.jar:5.0.9.RELEASE]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:660) ~[servlet-api.jar:na]
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:851) ~[spring-webmvc-5.0.9.RELEASE.jar:5.0.9.RELEASE]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:741) ~[servlet-api.jar:na]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) ~[catalina.jar:9.0.14]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[catalina.jar:9.0.14]
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) ~[tomcat-websocket.jar:9.0.14]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[catalina.jar:9.0.14]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[catalina.jar:9.0.14]
at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:712) ~[catalina.jar:9.0.14]
at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:459) ~[catalina.jar:9.0.14]
at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:384) ~[catalina.jar:9.0.14]
at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:312) ~[catalina.jar:9.0.14]
at org.springframework.boot.web.servlet.support.ErrorPageFilter.handleErrorStatus(ErrorPageFilter.java:164) ~[spring-boot-2.0.5.RELEASE.jar:2.0.5.RELEASE]
at org.springframework.boot.web.servlet.support.ErrorPageFilter.doFilter(ErrorPageFilter.java:132) ~[spring-boot-2.0.5.RELEASE.jar:2.0.5.RELEASE]
at org.springframework.boot.web.servlet.support.ErrorPageFilter.access$000(ErrorPageFilter.java:66) ~[spring-boot-2.0.5.RELEASE.jar:2.0.5.RELEASE]
at org.springframework.boot.web.servlet.support.ErrorPageFilter$1.doFilterInternal(ErrorPageFilter.java:105) ~[spring-boot-2.0.5.RELEASE.jar:2.0.5.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.0.9.RELEASE.jar:5.0.9.RELEASE]
at org.springframework.boot.web.servlet.support.ErrorPageFilter.doFilter(ErrorPageFilter.java:123) ~[spring-boot-2.0.5.RELEASE.jar:2.0.5.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[catalina.jar:9.0.14]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[catalina.jar:9.0.14]
at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:200) ~[spring-web-5.0.9.RELEASE.jar:5.0.9.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.0.9.RELEASE.jar:5.0.9.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[catalina.jar:9.0.14]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[catalina.jar:9.0.14]
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:199) ~[catalina.jar:9.0.14]
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) ~[catalina.jar:9.0.14]
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:490) ~[catalina.jar:9.0.14]
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139) ~[catalina.jar:9.0.14]
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) ~[catalina.jar:9.0.14]
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:668) ~[catalina.jar:9.0.14]
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) ~[catalina.jar:9.0.14]
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343) ~[catalina.jar:9.0.14]
at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:408) ~[tomcat-coyote.jar:9.0.14]
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) ~[tomcat-coyote.jar:9.0.14]
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:834) ~[tomcat-coyote.jar:9.0.14]
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1417) ~[tomcat-coyote.jar:9.0.14]
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) ~[tomcat-coyote.jar:9.0.14]
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) ~[na:na]
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) ~[na:na]
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) ~[tomcat-util.jar:9.0.14]
at java.base/java.lang.Thread.run(Thread.java:834) ~[na:na]
第43行对应于：
return usuario.findBy("username", SecurityContextHolder.getContext().getAuthentication().getName());
被调用时导致此错误的方法之一是：
@RequestMapping("download/{id}")
@ResponseBody
public byte[] download(@PathVariable("id") Integer id) throws IOException {
return this.serv.download(id);
}
有人知道如何解决这个问题吗？
答案 0 :(得分：0)
如果不存在身份验证，则SecurityContext为getAuthentication（）返回NULL。如果您合并公共页面和非公共页面的代码，请确保您的应用程序可以处理此问题。
返回：身份验证；如果没有可用的身份验证信息，则返回null