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沃梦达建站-编程问答-Java开发问题-正文

为什么我的 loginService 为空?

2023-09-25Java开发问题
2
本文介绍了为什么我的 loginService 为空?的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着跟版网的小编来一起学习吧！

问题描述

我有一个像这样的 LoginService 类:

I have a LoginService class like this:

@Service("loginService")
public class LoginService {

public boolean isValidUser(CustomerDTO customerDTO){
    if(customerDTO.getUsername().equals("admin") && 
            customerDTO.getPassword().equals("admin")){
                return true;
            }
    return false;
   }
}

还有一个像这样的 LoginAction 类:

And a LoginAction class like this:

@Controller
public class LoginAction{

private CustomerDTO customerDTO;
@Autowired
private LoginService loginService;

public CustomerDTO getCustomerDTO() {
    return customerDTO;
}

public void setCustomerDTO(CustomerDTO customerDTO) {
    this.customerDTO = customerDTO;
}

public String execute(){
    if(loginService.isValidUser(this.getCustomerDTO())){
        return "success";           
    }
    return "failure";
  }
}

当我尝试从 LoginAction 类调用方法 isValidUser 时出现空指针异常.那是因为我的 loginService 对象是 null.我做错了什么?

I get a null pointer exception when I try to call the method isValidUser from LoginAction class. That is because my loginService object is null. What am I doing wrong?

这是我的异常堆栈:

java.lang.NullPointerException 
com.sc.web.LoginAction.execute(LoginAction.java:26)
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
java.lang.reflect.Method.invoke(Method.java:483)
com.opensymphony.xwork2.DefaultActionInvocation.invokeAction(DefaultActionInvocation.java:450)
com.opensymphony.xwork2.DefaultActionInvocation.invokeActionOnly(DefaultActionInvocation.java:289)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:252)
org.apache.struts2.interceptor.DeprecationInterceptor.intercept(DeprecationInterceptor.java:41)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)
org.apache.struts2.interceptor.debugging.DebuggingInterceptor.intercept(DebuggingInterceptor.java:256)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)
com.opensymphony.xwork2.interceptor.DefaultWorkflowInterceptor.doIntercept(DefaultWorkflowInterceptor.java:167)
com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)
com.opensymphony.xwork2.validator.ValidationInterceptor.doIntercept(ValidationInterceptor.java:265)
org.apache.struts2.interceptor.validation.AnnotationValidationInterceptor.doIntercept(AnnotationValidationInterceptor.java:68)
com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)
com.opensymphony.xwork2.interceptor.ConversionErrorInterceptor.intercept(ConversionErrorInterceptor.java:138)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)
com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:249)
com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)
com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:249)
com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)
com.opensymphony.xwork2.interceptor.StaticParametersInterceptor.intercept(StaticParametersInterceptor.java:191)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)
org.apache.struts2.interceptor.MultiselectInterceptor.intercept(MultiselectInterceptor.java:73)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)
org.apache.struts2.interceptor.CheckboxInterceptor.intercept(CheckboxInterceptor.java:91)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)
org.apache.struts2.interceptor.FileUploadInterceptor.intercept(FileUploadInterceptor.java:252)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)
com.opensymphony.xwork2.interceptor.ModelDrivenInterceptor.intercept(ModelDrivenInterceptor.java:100)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)
com.opensymphony.xwork2.interceptor.ScopedModelDrivenInterceptor.intercept(ScopedModelDrivenInterceptor.java:141)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)
com.opensymphony.xwork2.interceptor.ChainingInterceptor.intercept(ChainingInterceptor.java:145)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)
com.opensymphony.xwork2.interceptor.PrepareInterceptor.doIntercept(PrepareInterceptor.java:171)
com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)
com.opensymphony.xwork2.interceptor.I18nInterceptor.intercept(I18nInterceptor.java:139)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)
org.apache.struts2.interceptor.ServletConfigInterceptor.intercept(ServletConfigInterceptor.java:164)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)
com.opensymphony.xwork2.interceptor.AliasInterceptor.intercept(AliasInterceptor.java:193)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)
com.opensymphony.xwork2.interceptor.ExceptionMappingInterceptor.intercept(ExceptionMappingInterceptor.java:189)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)
org.apache.struts2.impl.StrutsActionProxy.execute(StrutsActionProxy.java:54)
org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:562)
org.apache.struts2.dispatcher.ng.ExecuteOperations.executeAction(ExecuteOperations.java:77)
org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:99)
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:953)
org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1023)
org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310)
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
java.lang.Thread.run(Thread.java:745)

推荐答案

从堆栈跟踪可以看出您没有使用 struts-spring 集成.Struts 和 spring 通过 spring 插件 集成.Struts 默认按名称自动装配.

From the stacktrace it's seen that you didn't use a struts-spring integration. Struts and spring are integrated via spring plugin. Struts by default autowires by name.

Spring 插件通过覆盖 Struts ObjectFactory 来增强核心框架对象的创建.当一个对象被创建时，它使用 Struts 配置中的 class 属性来对应 Spring 配置中的 id 属性.如果没有找到，该类将尝试照常创建，然后由 Spring 自动装配.对于 Actions，Spring 2 的 bean 范围特性可用于将 Action 实例范围限定为会话、应用程序或自定义范围，在默认的每个请求范围之外提供高级自定义.

The Spring Plugin works by overriding the Struts ObjectFactory to enhance the creation of core framework objects. When an object is to be created, it uses the class attribute in the Struts configuration to correspond to the id attribute in the Spring configuration. If not found, the class will try to be created as usual, then be autowired by Spring. In the case of Actions, Spring 2's bean scope feature can be used to scope an Action instance to the session, application, or a custom scope, providing advanced customization above the default per-request scoping.

要使用插件，只需将其添加到类路径中.

To use a plugin just add it to the classpath.

要启用 Spring 集成，只需在您的应用程序中包含 struts2-spring-plugin-x-x-x.jar.

To enable Spring integration, simply include struts2-spring-plugin-x-x-x.jar in your application.

这篇关于为什么我的 loginService 为空?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持跟版网！

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