Java bean 实例化失败；嵌套异常是 org.springframework.beans.BeanInstantiationException：

Instantiation of bean failed; nested exception is org.springframework.beans.BeanInstantiationException:

提问by emoleumassi

i have some problem with my constructor in one my controller. I try to call one service in a constructor. The Service is autowired in an AbstractController, but i got a nullpointer exception.

我的一个控制器中的构造函数有一些问题。我尝试在构造函数中调用一项服务。该服务在 AbstractController 中自动装配，但我得到了一个空指针异常。

A component:

一个组件：

@Component
@RestController
@RequestMapping(value = "/test", ...)
public class AController extends AbstractController {

    @Autowired
    SomeService someService;

    public AController(){
        globalService.setClazz(Test.class);
    }
....

here the AbstractController:

这里是抽象控制器：

public abstract class AbstractController<T> {

    @Autowired
    GlobalService globalService;

    ...

here the exception. It is throwed in by globalService.setClazz(Test.class);

这里例外。它被扔进去globalService.setClazz(Test.class);

 Instantiation of bean failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.x.server.controller.AController]: Constructor threw exception; nested exception is java.lang.NullPointerException -> [Help 1]
org.apache.maven.lifecycle.LifecycleExecutionException: Failed to execute goal org.springframework.boot:spring-boot-maven-plugin:1.3.1.RELEASE:run (default-cli) on project eza: An exception occurred while running. null
        at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:216)
        at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:153)
        at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:145)
        at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:116)
        at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:80)
        at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build(SingleThreadedBuilder.java:51)
        at org.apache.maven.lifecycle.internal.LifecycleStarter.execute(LifecycleStarter.java:128)
        at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:307)
        at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:193)
        at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:106)
        at org.apache.maven.cli.MavenCli.execute(MavenCli.java:862)
        at org.apache.maven.cli.MavenCli.doMain(MavenCli.java:286)
        at org.apache.maven.cli.MavenCli.main(MavenCli.java:197)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:497)
        at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced(Launcher.java:289)
        at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:229)
        at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode(Launcher.java:415)
        at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:356)
Caused by: org.apache.maven.plugin.MojoExecutionException: An exception occurred while running. null
        at org.springframework.boot.maven.AbstractRunMojo$IsolatedThreadGroup.rethrowUncaughtException(AbstractRunMojo.java:438)
        at org.springframework.boot.maven.RunMojo.runWithMavenJvm(RunMojo.java:61)
        at org.springframework.boot.maven.AbstractRunMojo.run(AbstractRunMojo.java:215)
        at org.springframework.boot.maven.AbstractRunMojo.execute(AbstractRunMojo.java:174)
        at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:134)
        at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:208)
        ... 20 more
Caused by: java.lang.reflect.InvocationTargetException
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:497)
        at org.springframework.boot.maven.AbstractRunMojo$LaunchRunner.run(AbstractRunMojo.java:467)
        at java.lang.Thread.run(Thread.java:745)
Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'movieController' defined in file [...com/x/server/controller/AController.class]: Instantiation of bean failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.x.server.controller.AController]: Constructor threw exception; nested exception is java.lang.NullPointerException
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:1105)
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1050)
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:510)
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:482)
        at org.springframework.beans.factory.support.AbstractBeanFactory.getObject(AbstractBeanFactory.java:306)
        at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
        at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:302)
        at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:197)
        at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:772)
        at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:839)
        at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:538)
        at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.refresh(EmbeddedWebApplicationContext.java:118)
        at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:764)
        at org.springframework.boot.SpringApplication.doRun(SpringApplication.java:357)
        at org.springframework.boot.SpringApplication.run(SpringApplication.java:305)
        at org.springframework.boot.builder.SpringApplicationBuilder.run(SpringApplicationBuilder.java:134)
        at com.x.server.Application.main(Application.java:36)
        ... 6 more
Caused by: org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.x.server.controller.AController]: Constructor threw exception; nested exception is java.lang.NullPointerException
        at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:163)
        at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:89)
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:1098)
        ... 22 more
Caused by: java.lang.NullPointerException
        at com.x.server.controller.AController.<init>(AController.java:40)
        at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
        at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
        at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
        at java.lang.reflect.Constructor.newInstance(Constructor.java:422)
        at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:147)
        ... 24 more

Thanks for helping

谢谢你的帮助

采纳答案by Roman

You are using globalServicefield inside the constructor, but the constructor is called before any @Autowiredfields are set, so globalServiceis nullat that point.

您正在使用globalService领域的构造函数中，但是任何之前调用构造函数@Autowired设置的字段，所以globalService是null在这一点上。

You should probably use

你可能应该使用

@PostConstruct
public void init() {
    globalService.setClazz(Test.class);
}

instead of the constructor. Or better, do this setup at the same place where GlobalServiceis created.

而不是构造函数。或者更好的是，在GlobalService创建的同一位置执行此设置。

回答by user1610338

Put the @Componentannotation in your super class as well. These annotations deal with the class they are applied to and does not affect their parent class. So the @Autowiredhas no effect in the parent class

也将@Component注释放在您的超类中。这些注解处理它们应用到的类并且不影响它们的父类。所以@Autowired在父类中没有影响