因为某个Bean为空，无法启动Spring Boot应用
我在让一个应用程序运行时遇到了问题。
我正在使用Spring 5来运行一个使用SOAP的 Spring Boot应用。它运行在Java 17上。它在启动时就退出，因为在创建一个类时发生了空指针异常（NullPointerException）而导致“无法创建类”的错误：``` org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'soapCategoryService' defined in file [C:\Development\sap.metadata.plugins\org.eclipse.wst.server.core\tmp0\wtpwebapps\sapauthorize\WEB-INF\classes\ll\sapauthorization\services\soap\SoapCategoryService.class]: Invocation of init method failed; nested exception is java.lang.NullPointerException: Cannot invoke "javax.xml.soap.MessageFactory.createMessage()" because "this.messageFactory" is null at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1804) ~[spring-beans-5.3.27.jar:5.3.27]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:620) ~[spring-beans-5.3.27.jar:5.3.27]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:542) ~[spring-beans-5.3.27.jar:5.3.27]
at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:335) ~[spring-beans-5.3.27.jar:5.3.27]
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234) ~[spring-beans-5.3.27.jar:5.3.27]
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:333) ~[spring-beans-5.3.27.jar:5.3.27]
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:208) ~[spring-beans-5.3.27.jar:5.3.27]
at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:955) ~[spring-beans-5.3.27.jar:5.3.27]
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:920) ~[spring-context-5.3.27.jar:5.3.27]
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:583) ~[spring-context-5.3.27.jar:5.3.27]
at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:147) ~[spring-boot-2.7.11.jar:2.7.11]
at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:731) ~[spring-boot-2.7.11.jar:2.7.11]
at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:408) ~[spring-boot-2.7.11.jar:2.7.11]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:307) ~[spring-boot-2.7.11.jar:2.7.11]
at org.springframework.boot.web.servlet.support.SpringBootServletInitializer.run(SpringBootServletInitializer.java:175) ~[spring-boot-2.7.11.jar:2.7.11]
at org.springframework.boot.web.servlet.support.SpringBootServletInitializer.createRootApplicationContext(SpringBootServletInitializer.java:155) ~[spring-boot-2.7.11.jar:2.7.11]
at org.springframework.boot.web.servlet.support.SpringBootServletInitializer.onStartup(SpringBootServletInitializer.java:97) ~[spring-boot-2.7.11.jar:2.7.11]
at org.springframework.web.SpringServletContainerInitializer.onStartup(SpringServletContainerInitializer.java:174) ~[spring-web-5.3.27.jar:5.3.27]
at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:4479) ~[catalina.jar:9.0.113]
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:164) ~[catalina.jar:9.0.113]
at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1201) ~[catalina.jar:9.0.113]
at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1191) ~[catalina.jar:9.0.113]
at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264) ~[na:na]
at org.apache.tomcat.util.threads.InlineExecutorService.execute(InlineExecutorService.java:82) ~[tomcat-util.jar:9.0.113]
at java.base/java.util.concurrent.AbstractExecutorService.submit(AbstractExecutorService.java:145) ~[na:na]
at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:747) ~[catalina.jar:9.0.113]
at org.apache.catalina.core.StandardHost.startInternal(StandardHost.java:726) ~[catalina.jar:9.0.113]
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:164) ~[catalina.jar:9.0.113]
at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1201) ~[catalina.jar:9.0.113]
at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1191) ~[catalina.jar:9.0.113]
at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264) ~[na:na]
at org.apache.tomcat.util.threads.InlineExecutorService.execute(InlineExecutorService.java:82) ~[tomcat-util.jar:9.0.113]
at java.base/java.util.concurrent.AbstractExecutorService.submit(AbstractExecutorService.java:145) ~[na:na]
at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:747) ~[catalina.jar:9.0.113]
at org.apache.catalina.core.StandardEngine.startInternal(StandardEngine.java:209) ~[catalina.jar:9.0.113]
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:164) ~[catalina.jar:9.0.113]
at org.apache.catalina.core.StandardService.startInternal(StandardService.java:410) ~[catalina.jar:9.0.113]
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:164) ~[catalina.jar:9.0.113]
at org.apache.catalina.core.StandardServer.startInternal(StandardServer.java:872) ~[catalina.jar:9.0.113]
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:164) ~[catalina.jar:9.0.113]
at org.apache.catalina.startup.Catalina.start(Catalina.java:736) ~[catalina.jar:9.0.113]
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77) ~[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:569) ~[na:na]
at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:342) ~[bootstrap.jar:9.0.113]
at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:473) ~[bootstrap.jar:9.0.113]
Caused by: java.lang.NullPointerException: Cannot invoke "javax.xml.soap.MessageFactory.createMessage()" because "this.messageFactory" is null
at org.springframework.ws.soap.saaj.SaajSoapMessageFactory.createWebServiceMessage(SaajSoapMessageFactory.java:167) ~[spring-ws-core-3.1.6.jar:na]
at org.springframework.ws.soap.saaj.SaajSoapMessageFactory.createWebServiceMessage(SaajSoapMessageFactory.java:61) ~[spring-ws-core-3.1.6.jar:na]
at org.springframework.ws.context.DefaultMessageContext.
at org.springframework.ws.client.core.WebServiceTemplate.sendAndReceive(WebServiceTemplate.java:536) ~[spring-ws-core-3.1.6.jar:na]
at org.springframework.ws.client.core.WebServiceTemplate.sendAndReceive(WebServiceTemplate.java:523) ~[spring-ws-core-3.1.6.jar:na]
at ll.sapauthorization.services.soap.SoapService.sendAndReceive(SoapService.java:63) ~[classes/:2.0]
at ll.sapauthorization.services.soap.SoapCategoryService.populateCache(SoapCategoryService.java:153) ~[classes/:2.0]
at ll.sapauthorization.services.soap.SoapCategoryService.afterPropertiesSet(SoapCategoryService.java:85) ~[classes/:2.0]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1863) ~[spring-beans-5.3.27.jar:5.3.27]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1800) ~[spring-beans-5.3.27.jar:5.3.27]
... 46 common frames omitted
我知道问题所在：在应用启动时，SoapCategoryService 类使用的消息工厂没有被创建。我已经尝试使用 @Autowired 注解来创建消息工厂，但这并未解决问题。显然，MessageFactory 对象是在一个名为 SaajSoapMessageFactory 的类中创建的——这是一个我无法修改的 Spring 框架类！因此，我无法将带有 @Autowired 的 MessageFactory 对象添加到它中，从而也无法让 MessageFactory 被创建。
有人有办法解决这个问题吗？之前有人遇到过吗？如果遇到过，你是如何解决的（如果你确实解决了的话）？
注：给关闭我问题的那位：
1. 链接 [What is a NullPointerException, and how do I fix it?](https://stackoverflow.com/questions/218384/what-is-a-nullpointerexception-and-how-do-i-fix-it) 并没有解决我的问题，因为我不是在问“为什么会抛出 NullPointerException”。我知道 NullPointerException 是什么，以及应该怎么修复。问题在于，当修复需要在一个我无法编辑的 .jar 库中的代码里进行时，如何做到！正如我所说：自动装配显然必须在名为 SaajSoapMessageFactory 的类中完成——它是 Spring Framework 的一部分。我真正需要的不是关于 NullPointerExceptions 的基础信息，而是知道在我无法编辑（且不修改 Spring Framework）的类中需要自动装配时，如何避免被自动装配的类为 null。
2. 请注意，由于空指针异常是在 Spring 框架内部抛出的，原因是在需要在 Spring 框架类中完成自动装配的情况下，相关代码是 SaajSoapMessageFactory 类，它属于 Spring Framework 的开发者。
3. 另外，请注意，如我所述，我确实尝试对 MessageFactory 类进行自动装配。为此，我必须在名为 SSConfig.java 的类中创建一个 bean，如下所示：
@Configuration public class SSConfig { . . . @Bean public MessageFactory messageFactory() throws SOAPException { return(MessageFactory.newInstance()); } } ```
这使得你链接中的答案 Why is my Spring @Autowired field null? 不再适用。如果我没有尝试过这个，我就不会来问这个问题。
解决方案
你的错误信息写着 Caused by: java.lang.NullPointerException: Cannot invoke "javax.xml.soap.MessageFactory.createMessage()" because "this.messageFactory" is null。
正如 这条StackOverflow回答 所说，SAAJ (javax.xml.soap.*) 已在Java 11中从JDK中移除了。
你可以尝试在项目中添加 javax.xml.soap 依赖，但我不知道这是否能按预期工作。如果可以，你应该迁移到Spring Web Services 5.x（https://docs.spring.io/spring-ws/docs/current/reference/html/）
或者，（前提是你的项目中已有 javax.xml.soap 依赖），如评论中的 @George Lvov所述，你可以使用 这个回答 的示例来创建一个托管的bean。
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