Maven NoClassDefFoundError

使用 Maven 经常会莫名其妙的出现 NoClassDefFoundError，就像下面这种：

2018-08-20 11:00:26.230 [main] ERROR o.s.boot.SpringApplication - Application run failed
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'messageConverters' defined in class path resource [org/springframework/boot/autoconfigure/http/HttpMessageConvertersAutoConfiguration.class]: Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.springframework.boot.autoconfigure.http.HttpMessageConverters]: Factory method 'messageConverters' threw exception; nested exception is java.lang.NoClassDefFoundError: com/fasterxml/jackson/databind/exc/InvalidDefinitionException
    at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:590)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1247)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1096)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:535)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:495)
    at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:317)
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:315)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:759)
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:869)
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:550)
    at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:762)
    at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:398)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:330)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1258)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1246)
    at com.xxx.xxx.mqservices.Application.main(Application.java:16)
Caused by: org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.springframework.boot.autoconfigure.http.HttpMessageConverters]: Factory method 'messageConverters' threw exception; nested exception is java.lang.NoClassDefFoundError: com/fasterxml/jackson/databind/exc/InvalidDefinitionException
    at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:185)
    at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:582)
    ... 17 common frames omitted
Caused by: java.lang.NoClassDefFoundError: com/fasterxml/jackson/databind/exc/InvalidDefinitionException
    at org.springframework.http.converter.support.AllEncompassingFormHttpMessageConverter.<init>(AllEncompassingFormHttpMessageConverter.java:88)
    at org.springframework.web.client.RestTemplate.<init>(RestTemplate.java:179)
    at org.springframework.boot.autoconfigure.http.HttpMessageConverters.getDefaultConverters(HttpMessageConverters.java:204)
    at org.springframework.boot.autoconfigure.http.HttpMessageConverters.<init>(HttpMessageConverters.java:106)
    at org.springframework.boot.autoconfigure.http.HttpMessageConverters.<init>(HttpMessageConverters.java:92)
    at org.springframework.boot.autoconfigure.http.HttpMessageConvertersAutoConfiguration.messageConverters(HttpMessageConvertersAutoConfiguration.java:72)
    at org.springframework.boot.autoconfigure.http.HttpMessageConvertersAutoConfiguration$$EnhancerBySpringCGLIB$$73928262.CGLIB$messageConverters$0(<generated>)
    at org.springframework.boot.autoconfigure.http.HttpMessageConvertersAutoConfiguration$$EnhancerBySpringCGLIB$$73928262$$FastClassBySpringCGLIB$$33286c75.invoke(<generated>)
    at org.springframework.cglib.proxy.MethodProxy.invokeSuper(MethodProxy.java:228)
    at org.springframework.context.annotation.ConfigurationClassEnhancer$BeanMethodInterceptor.intercept(ConfigurationClassEnhancer.java:361)
    at org.springframework.boot.autoconfigure.http.HttpMessageConvertersAutoConfiguration$$EnhancerBySpringCGLIB$$73928262.messageConverters(<generated>)
    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:498)
    at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:154)
    ... 18 common frames omitted
Caused by: java.lang.ClassNotFoundException: com.fasterxml.jackson.databind.exc.InvalidDefinitionException
    at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
    ... 34 common frames omitted

重点是最后一条消息，可以看出应该是 jackson 相关的包出问题了：

Caused by: java.lang.ClassNotFoundException: com.fasterxml.jackson.databind.exc.InvalidDefinitionException

这种一般是由于 Maven 依赖的包有冲突导致的。可以使用如下命令来查找是哪里的依赖出了问题。

mvn dependency:tree -Dverbose

运行得到如下结果：

[INFO] Scanning for projects...
[INFO]
[INFO] -------------------< com.xxx:XxxMqServices >--------------------
[INFO] Building XxxMqServices 1.0-SNAPSHOT
[INFO] --------------------------------[ jar ]---------------------------------
...
[INFO]    +- org.elasticsearch:elasticsearch:jar:5.6.10:compile
...
[INFO]    |  +- com.fasterxml.jackson.core:jackson-core:jar:2.9.6:compile
[INFO]    |  +- com.fasterxml.jackson.dataformat:jackson-dataformat-smile:jar:2.9.6:compile
[INFO]    |  +- com.fasterxml.jackson.dataformat:jackson-dataformat-yaml:jar:2.9.6:compile
[INFO]    |  +- com.fasterxml.jackson.dataformat:jackson-dataformat-cbor:jar:2.9.6:compile
...
[INFO]    +- org.codehaus.jackson:jackson-mapper-asl:jar:1.9.2:compile
[INFO]    |  \- org.codehaus.jackson:jackson-core-asl:jar:1.9.2:compile
...
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------

可以看到 org.elasticsearch:elasticsearch 包依赖了 com.fasterxml.jackson.core:jackson-core🫙2.9.6 ，而别得地方又同时依赖了 org.codehaus.jackson:jackson-core-asl🫙1.9.2 。

jackson-mapper-asl 最高版本是 1.9.13，而且已经迁移到了 jackson-databind 项目。所以将依赖从

<dependency>
    <groupId>org.codehaus.jackson</groupId>
    <artifactId>jackson-mapper-asl</artifactId>
    <version>1.9.2</version>
</dependency>

改成

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.9.6</version>
</dependency>

问题就解决了。