1. 复现问题
今天在启动spring boot项目时，出现如下错误：
org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'mappingJackson2HttpMessageConverter' defined in class path resource [org/springframework/boot/autoconfigure/http/JacksonHttpMessageConvertersConfiguration$MappingJackson2HttpMessageConverterConfiguration.class]: Unsatisfied dependency expressed through method 'mappingJackson2HttpMessageConverter' parameter 0; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'jacksonObjectMapper' defined in class path resource [org/springframework/boot/autoconfigure/jackson/JacksonAutoConfiguration$JacksonObjectMapperConfiguration.class]: Post-processing of merged bean definition failed; nested exception is java.lang.IllegalStateException: Failed to introspect Class [com.fasterxml.jackson.databind.ObjectMapper] from ClassLoader [sun.misc.Launcher$AppClassLoader@18b4aac2]
at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:800)
at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:541)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1334)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1177)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:564)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:524)
at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:335)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:333)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:208)
at org.springframework.beans.factory.config.DependencyDescriptor.resolveCandidate(DependencyDescriptor.java:276)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.addCandidateEntry(DefaultListableBeanFactory.java:1605)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.findAutowireCandidates(DefaultListableBeanFactory.java:1562)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveMultipleBeans(DefaultListableBeanFactory.java:1406)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1338)
at org.springframework.beans.factory.support.DefaultListableBeanFactory$DependencyObjectProvider.resolveStream(DefaultListableBeanFactory.java:2108)
at org.springframework.beans.factory.support.DefaultListableBeanFactory$DependencyObjectProvider.orderedStream(DefaultListableBeanFactory.java:2102)
at org.springframework.boot.autoconfigure.http.HttpMessageConvertersAutoConfiguration.messageConverters(HttpMessageConvertersAutoConfiguration.java:70)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:154)
... 45 common frames omitted
Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'jacksonObjectMapper' defined in class path resource [org/springframework/boot/autoconfigure/jackson/JacksonAutoConfiguration$JacksonObjectMapperConfiguration.class]: Post-processing of merged bean definition failed; nested exception is java.lang.IllegalStateException: Failed to introspect Class [com.fasterxml.jackson.databind.ObjectMapper] from ClassLoader [sun.misc.Launcher$AppClassLoader@18b4aac2]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:579)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:524)
at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:335)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:333)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:208)
at org.springframework.beans.factory.config.DependencyDescriptor.resolveCandidate(DependencyDescriptor.java:276)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1380)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1300)
at org.springframework.beans.factory.support.ConstructorResolver.resolveAutowiredArgument(ConstructorResolver.java:887)
at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:791)
... 67 common frames omitted
Caused by: java.lang.IllegalStateException: Failed to introspect Class [com.fasterxml.jackson.databind.ObjectMapper] from ClassLoader [sun.misc.Launcher$AppClassLoader@18b4aac2]
at org.springframework.util.ReflectionUtils.getDeclaredMethods(ReflectionUtils.java:481)
at org.springframework.util.ReflectionUtils.doWithLocalMethods(ReflectionUtils.java:321)
at org.springframework.beans.factory.annotation.InitDestroyAnnotationBeanPostProcessor.buildLifecycleMetadata(InitDestroyAnnotationBeanPostProcessor.java:232)
at org.springframework.beans.factory.annotation.InitDestroyAnnotationBeanPostProcessor.findLifecycleMetadata(InitDestroyAnnotationBeanPostProcessor.java:210)
at org.springframework.beans.factory.annotation.InitDestroyAnnotationBeanPostProcessor.postProcessMergedBeanDefinition(InitDestroyAnnotationBeanPostProcessor.java:149)
at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.postProcessMergedBeanDefinition(CommonAnnotationBeanPostProcessor.java:294)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyMergedBeanDefinitionPostProcessors(AbstractAutowireCapableBeanFactory.java:1098)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:576)
... 77 common frames omitted
Caused by: java.lang.NoClassDefFoundError: com/fasterxml/jackson/core/exc/StreamWriteException
at java.lang.Class.getDeclaredMethods0(Native Method)
at java.lang.Class.privateGetDeclaredMethods(Class.java:2701)
at java.lang.Class.getDeclaredMethods(Class.java:1975)
at org.springframework.util.ReflectionUtils.getDeclaredMethods(ReflectionUtils.java:463)
... 84 common frames omitted
Caused by: java.lang.ClassNotFoundException: com.fasterxml.jackson.core.exc.StreamWriteException
at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
... 88 common frames omitted
即Error creating bean with name 'mappingJackson2HttpMessageConverter' defined in class path resource 这个问题，但从这个错误信息，根本看不到具体的错误。
因而，继续往下看错误日志，看到最后发现报了这个错误，如下图所示：
2. 分析问题
java.lang.ClassNotFoundException: com.fasterxml.jackson.core.exc.StreamWriteException。出现这个错误，一般会有如下三种情况：
- 版本不兼容
spring的版本和jackson的版本不兼容导致的。
- jackson包冲突导致的
- 如何查看maven的包冲突？
可以使用快捷键Ctrl+Shift+Alt+U，或者是打开pom.xml,右键选择maven，然后选择Show Dependencies。
- 进入依赖包结构之后，可以用走上方的加减图标进行放大和缩小
- 红线的就是有冲突的包，可以选择右键—>exclude，把冲突的包排除掉
- 剔除冲突的包，回到
pom.xml进行刷新后，冲突的包就被排除了
- 缺少相应的依赖
我查看我的pom文件，果然没有相应的依赖。
3. 解决问题
既然缺少相应的依赖，加上如下依赖即可：
<!-- properties中增加jackson.version，便于dependncy调用 -->
<properties>
<java.version>1.8</java.version>
<jackson.version>2.10.1</jackson.version>
</properties>
<!-- jackson -->
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-databind</artifactId>
<version>${jackson.verson}</version>
</dependency>
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-core</artifactId>
<version>${jackson.verson}</version>
</dependency>
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-annotations</artifactId>
<version>${jackson.verson}</version>
</dependency>
