问题描述
这有点奇怪,但是当我尝试实例化DatePicker组件时,我会直接上Nullpointerexception
:
DatePicker date = new DatePicker("Select date",LocalDate.Now());
就这样,我进入了这一行(我已经在构造函数中尝试了不同的参数,并且也尝试了默认构造函数,但其中没有任何内容),并且由于Nullpointer而导致我的应用程序无法启动...
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'lectureForm' defined in file [D:\IDEAProjects\university\target\classes\com\university\ui\views\forms\LectureForm.class]: Bean instantiation via constructor Failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.university.ui.views.forms.LectureForm]: Constructor threw exception; nested exception is java.lang.NullPointerException
at org.springframework.beans.factory.support.ConstructorResolver.instantiate(ConstructorResolver.java:313)
at org.springframework.beans.factory.support.ConstructorResolver.autowireConstructor(ConstructorResolver.java:294)
at org.springframework.beans.factory.support.AbstractAutowireCapablebeanfactory.autowireConstructor(AbstractAutowireCapablebeanfactory.java:1358)
at org.springframework.beans.factory.support.AbstractAutowireCapablebeanfactory.createBeanInstance(AbstractAutowireCapablebeanfactory.java:1204)
at org.springframework.beans.factory.support.AbstractAutowireCapablebeanfactory.doCreateBean(AbstractAutowireCapablebeanfactory.java:557)
at org.springframework.beans.factory.support.AbstractAutowireCapablebeanfactory.createBean(AbstractAutowireCapablebeanfactory.java:517)
at org.springframework.beans.factory.support.Abstractbeanfactory.lambda$doGetBean$0(Abstractbeanfactory.java:323)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:226)
at org.springframework.beans.factory.support.Abstractbeanfactory.doGetBean(Abstractbeanfactory.java:321)
at org.springframework.beans.factory.support.Abstractbeanfactory.getBean(Abstractbeanfactory.java:202)
at org.springframework.beans.factory.support.DefaultListablebeanfactory.preInstantiateSingletons(DefaultListablebeanfactory.java:893)
at org.springframework.context.support.AbstractApplicationContext.finishbeanfactoryInitialization(AbstractApplicationContext.java:879)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:551)
at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:143)
at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:758)
at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:750)
at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:397)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:315)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1237)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1226)
at com.university.Main.main(Main.java:13)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:566)
at org.springframework.boot.devtools.restart.RestartLauncher.run(RestartLauncher.java:49)
Caused by: org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.university.ui.views.forms.LectureForm]: Constructor threw exception; nested exception is java.lang.NullPointerException
at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:217)
at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:117)
at org.springframework.beans.factory.support.ConstructorResolver.instantiate(ConstructorResolver.java:309)
... 25 common frames omitted
Caused by: java.lang.NullPointerException: null
at com.vaadin.flow.component.datepicker.DatePicker.<init>(DatePicker.java:85)
at com.university.ui.views.forms.LectureForm.configureFormComponents(LectureForm.java:126)
at com.university.ui.views.forms.LectureForm.<init>(LectureForm.java:68)
at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:490)
at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:204)
... 27 common frames omitted
DatePicker中的第85行(始终是该行)是
this.setLabel(label);
在
public DatePicker(String label,LocalDate initialDate,Valuechangelistener<ComponentValueChangeEvent<DatePicker,LocalDate>> listener) {
this(initialDate);
this.setLabel(label);
this.addValuechangelistener(listener);
}
所以我不知道为什么会发生这种情况,为什么它总是相同的构造函数(与参数无关),为什么问题出在标签上,最重要的是如何解决(-:
非常感谢您
解决方法
问题的根源出乎意料的是我用来运行应用程序的Spring Boot。
在IDE(IntelliJ IDEA)中的行顺序不正确,但带有链接标记。因此,实际上Nullpointerexception
并不是在标签设置时抛出的,而是在方法UI.getCurrent()
被调用并且DataPicker
试图设置语言环境时抛出的。由于Spring(@SpringComponent
的原因,方法调用到达时尚未构建Vaadin UI,因此返回值为null
。解决方案:在类中添加@UIScope
批注。