Spring控制器中的NullPointerException異常

Question

我有簡單的Spring MVC應用程序。當我嘗試訪問

http://localhost:8080/paygate/transaction

我得到一個錯誤：

org.springframework.web.util.NestedServletException: Request processing failed; nested exception is java.lang.NullPointerException 
org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:656) 
org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:549) 
javax.servlet.http.HttpServlet.service(HttpServlet.java:617) 
javax.servlet.http.HttpServlet.service(HttpServlet.java:717) 
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:368) 
org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:109) 
org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:83) 
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:380) 
org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:97) 
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:380) 
org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:100) 
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:380) 
org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:78) 
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:380) 
org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:54) 
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:380) 
org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:35) 
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:380) 
org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:187) 
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:380) 
org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:105) 
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:380) 
org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:79) 
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:380) 
org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:169) 
org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:237) 
org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:167) 


root cause 

java.lang.NullPointerException 
net.ggonchar.paygate.web.FrontController.runTransactionPost(FrontController.java:52) 
net.ggonchar.paygate.web.FrontController.runTransactionGet(FrontController.java:60) 
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) 
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) 
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) 
java.lang.reflect.Method.invoke(Method.java:597) 
org.springframework.web.bind.annotation.support.HandlerMethodInvoker.invokeHandlerMethod(HandlerMethodInvoker.java:176) 
org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.invokeHandlerMethod(AnnotationMethodHandlerAdapter.java:426) 
org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.handle(AnnotationMethodHandlerAdapter.java:414) 
org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:790) 
org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:719) 
org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:644) 
org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:549) 
javax.servlet.http.HttpServlet.service(HttpServlet.java:617) 
javax.servlet.http.HttpServlet.service(HttpServlet.java:717) 
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:368) 
org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:109) 
org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:83) 
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:380) 
org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:97) 
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:380) 
org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:100) 
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:380) 
org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:78) 
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:380) 
org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:54) 
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:380) 
org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:35) 
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:380) 
org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:187) 
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:380) 
org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:105) 
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:380) 
org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:79) 
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:380) 
org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:169) 
org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:237) 
org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:167) 

我的web.xml：

<servlet> 
    <servlet-name>appServlet</servlet-name> 
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class> 
    <init-param> 
     <param-name>contextConfigLocation</param-name> 
     <param-value>/WEB-INF/spring/appServlet/servlet-context.xml</param-value> 
    </init-param> 
    <load-on-startup>1</load-on-startup> 
</servlet> 

<servlet-mapping> 
    <servlet-name>appServlet</servlet-name> 
    <url-pattern>/</url-pattern> 
</servlet-mapping> 

的servlet-context.xml中：

<!-- Enables the Spring MVC @Controller programming model --> 
<annotation-driven /> 
    <!-- Imports user-defined @Controller beans that process client requests --> 
<beans:import resource="controllers.xml" /> 

控制器.xml

<!-- Scans within the base package of the application for @Components to configure as beans --> 
<context:component-scan base-package="net.myapp.paygate.web" /> 

FrontController.java：

@Controller 
@RequestMapping("/") 
public class FrontController { 

private LogService logService; 
private TransactionService transactionService; 

@Autowired 
public FrontController(LogService logService) { 
    this.logService = logService; 
} 

@RequestMapping(method = RequestMethod.GET) 
public String viewLogsGet(Model model) { 
    List<Log> logs = java.util.Collections.emptyList(); 
    logs = logService.query(); 
    model.addAttribute("logs",logs); 
    return "viewLogs"; 
} 

@RequestMapping(method = RequestMethod.POST) 
public String viewLogsPost(Model model) { 
    return viewLogsGet(model); 
} 

@RequestMapping(value = "/transaction", method = RequestMethod.POST) 
public String runTransactionPost(/*Map<String, Object> map,*/ 
     @ModelAttribute("transaction") Transaction transaction, 
     BindingResult result) { 

    //map.put("transaction", new Transaction()); 
    if (transaction != null) 
     transactionService.startTransaction(transaction); 
    return "transaction"; 
} 

@RequestMapping(value = "/transaction", method = RequestMethod.GET) 
public String runTransactionGet(Map<String, Object> map, 
     @ModelAttribute("transaction") Transaction transaction, 
     BindingResult result) { 
    return runTransactionPost(/*map,*/transaction, result); 
} 

} 

Answer 1

你沒有任何東西注射進FrontController的transactionService領域。因此，在runTransactionPost方法中調用transactionService.startTransaction(transaction);時，它將是null。

您需要在那裏注入某些東西，或許使用注入LogService的現有構造函數，例如，

@Autowired 
public FrontController(LogService logService, TransactionService transactionService) { 
    this.logService = logService; 
    this.transactionService = transactionService; 
}