spring boot项目在tomcat启动问题

问题描述

今天在使用spring-boot项目的时候，将打好的war放置到tomcat启动的时候，报错，信息如下

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'tomcatEmbeddedServletContainerFactory' defined in class path resource [org/springframework/boot/autoconfigure/web/EmbeddedServletContainerAutoConfiguration$EmbeddedTomcat.class]: Initialization of bean failed; nested exception is java.lang.NullPointerException
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:564)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:483)
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.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:761)
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:867)
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:543)
    at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.refresh(EmbeddedWebApplicationContext.java:122)
    at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:737)
    at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:370)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:314)
    at org.springframework.boot.web.support.SpringBootServletInitializer.run(SpringBootServletInitializer.java:151)
    at org.springframework.boot.web.support.SpringBootServletInitializer.createRootApplicationContext(SpringBootServletInitializer.java:131)
    at org.springframework.boot.web.support.SpringBootServletInitializer.onStartup(SpringBootServletInitializer.java:86)
    at org.springframework.web.SpringServletContainerInitializer.onStartup(SpringServletContainerInitializer.java:169)
    at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5196)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
    at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:752)
    at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:728)
    at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:734)
    at org.apache.catalina.startup.HostConfig.deployWAR(HostConfig.java:952)
    at org.apache.catalina.startup.HostConfig$DeployWar.run(HostConfig.java:1823)
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
    at java.util.concurrent.FutureTask.run(FutureTask.java:266)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.NullPointerException: null
    at org.springframework.boot.context.embedded.EmbeddedServletContainerCustomizerBeanPostProcessor.getCustomizers(EmbeddedServletContainerCustomizerBeanPostProcessor.java:77)
    at org.springframework.boot.context.embedded.EmbeddedServletContainerCustomizerBeanPostProcessor.postProcessBeforeInitialization(EmbeddedServletContainerCustomizerBeanPostProcessor.java:67)
    at org.springframework.boot.context.embedded.EmbeddedServletContainerCustomizerBeanPostProcessor.postProcessBeforeInitialization(EmbeddedServletContainerCustomizerBeanPostProcessor.java:54)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyBeanPostProcessorsBeforeInitialization(AbstractAutowireCapableBeanFactory.java:409)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1620)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:555)
    ... 28 common frames omitted
    

问题分析

从错误原因上来看，EmbeddedServletContainerCustomizerBeanPostProcessor.getCustomizers()这个方法在在调用时候报出空指针
程序如下：

private Collection<EmbeddedServletContainerCustomizer> getCustomizers() {
        if (this.customizers == null) {
            // Look up does not include the parent context
            this.customizers = new ArrayList<EmbeddedServletContainerCustomizer>(
                    this.applicationContext
                            .getBeansOfType(EmbeddedServletContainerCustomizer.class,
                                    false, false)
                            .values());
            Collections.sort(this.customizers, AnnotationAwareOrderComparator.INSTANCE);
            this.customizers = Collections.unmodifiableList(this.customizers);
        }
        return this.customizers;
    }

这个类是一个BeanPostProcessor的实现类，空指针报在this.applicationContext.getBeansOfType(EmbeddedServletContainerCustomizer.class,false, false).values() ,values()的调用者为空，也就是applicationContext通过getBeanOfType方法并没有找到EmbeddedServletContainerCustomizer实例；
但是我们的目的是不想要内嵌的tomcat的，而且项目pom文件已经把spring内嵌的tomcat已经排除了，配置如下：

    <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
            <exclusions>
                <exclusion>
                    <groupId>org.apache.tomcat</groupId>
                    <artifactId>tomcat-jdbc</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
            <exclusions>
                <exclusion>
                    <groupId>org.apache.tomcat</groupId>
                    <artifactId>tomcat-jdbc</artifactId>
                </exclusion>
                <exclusion>
                    <groupId>org.springframework.boot</groupId>
                    <artifactId>spring-boot-starter-tomcat</artifactId>
                </exclusion>
            </exclusions>
        </dependency>

问题解决

后来看到maven的依赖发现了问题，虽然我们制定了spring-boot-dependencies的版本是1.5.4,但是实际上的spring-boot的版本是1.5.2，这和spring-boot-starter:1.5.4 和 spring-boot-web 1.5.4 都不一致。后来将spring-boot-dependencies的版本统一降到1.5.2后，不一致的问题解决，tomcat也正常启动了。

<dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-dependencies</artifactId>
                <version>1.5.4.RELEASE</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>

        </dependencies>
    </dependencyManagement>

后记：后台通过排除法发现是有一个优先级更高的地方声明spring-boot的版本号

spring-boot的GitHub上也有人遇到过相似问题，链接在此