SpringMVC练习JSON数据绑定时出现的问题

开门见山，原因如下，最下面是添加jar包的教程

根本原因是因为打包的工程内没有你pom新添加的依赖jar包

项目启动后报错如下

 idea内报错如下

26-Apr-2022 23:46:55.817 警告 [RMI TCP Connection(2)-127.0.0.1] org.springframework.context.support.AbstractApplicationContext.refresh Exception encountered during context initialization - cancelling refresh attempt: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter#0' defined in class path resource [spring-mvc.xml]: Cannot create inner bean 'org.springframework.http.converter.json.MappingJackson2HttpMessageConverter#42545a09' of type [org.springframework.http.converter.json.MappingJackson2HttpMessageConverter] while setting bean property 'messageConverters' with key [0]; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'org.springframework.http.converter.json.MappingJackson2HttpMessageConverter#42545a09': Lookup method resolution failed; nested exception is java.lang.IllegalStateException: Failed to introspect Class [org.springframework.http.converter.json.MappingJackson2HttpMessageConverter] from ClassLoader [ParallelWebappClassLoader
  context: MVC12_Web_exploded
  delegate: false
----------> Parent Classloader:
java.net.URLClassLoader@123772c4
]
26-Apr-2022 23:46:55.821 严重 [RMI TCP Connection(2)-127.0.0.1] org.springframework.web.servlet.FrameworkServlet.initServletBean Context initialization failed
	org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter#0' defined in class path resource [spring-mvc.xml]: Cannot create inner bean 'org.springframework.http.converter.json.MappingJackson2HttpMessageConverter#42545a09' of type [org.springframework.http.converter.json.MappingJackson2HttpMessageConverter] while setting bean property 'messageConverters' with key [0]; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'org.springframework.http.converter.json.MappingJackson2HttpMessageConverter#42545a09': Lookup method resolution failed; nested exception is java.lang.IllegalStateException: Failed to introspect Class [org.springframework.http.converter.json.MappingJackson2HttpMessageConverter] from ClassLoader [ParallelWebappClassLoader
  context: MVC12_Web_exploded
  delegate: false
----------> Parent Classloader:
java.net.URLClassLoader@123772c4
]
		at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveInnerBean(BeanDefinitionValueResolver.java:389)
		at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveValueIfNecessary(BeanDefinitionValueResolver.java:127)
		at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveManagedList(BeanDefinitionValueResolver.java:428)
		at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveValueIfNecessary(BeanDefinitionValueResolver.java:173)
		at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyPropertyValues(AbstractAutowireCapableBeanFactory.java:1697)
		at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1442)
		at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:593)
		at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:516)
		at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:324)
		at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:226)
		at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:322)
		at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:202)
		at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:897)
		at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:879)
		at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:551)
		at org.springframework.web.servlet.FrameworkServlet.configureAndRefreshWebApplicationContext(FrameworkServlet.java:702)
		at org.springframework.web.servlet.FrameworkServlet.createWebApplicationContext(FrameworkServlet.java:668)
		at org.springframework.web.servlet.FrameworkServlet.createWebApplicationContext(FrameworkServlet.java:716)
		at org.springframework.web.servlet.FrameworkServlet.initWebApplicationContext(FrameworkServlet.java:591)
		at org.springframework.web.servlet.FrameworkServlet.initServletBean(FrameworkServlet.java:530)
		at org.springframework.web.servlet.HttpServletBean.init(HttpServletBean.java:170)
		at javax.servlet.GenericServlet.init(GenericServlet.java:158)
		at org.apache.catalina.core.StandardWrapper.initServlet(StandardWrapper.java:1164)
		at org.apache.catalina.core.StandardWrapper.loadServlet(StandardWrapper.java:1117)
		at org.apache.catalina.core.StandardWrapper.load(StandardWrapper.java:1010)
		at org.apache.catalina.core.StandardContext.loadOnStartup(StandardContext.java:4957)
		at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5264)
		at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183)
		at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:726)
		at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:698)
		at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:696)
		at org.apache.catalina.startup.HostConfig.manageApp(HostConfig.java:1783)
		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.apache.tomcat.util.modeler.BaseModelMBean.invoke(BaseModelMBean.java:293)
		at com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.invoke(DefaultMBeanServerInterceptor.java:819)
		at com.sun.jmx.mbeanserver.JmxMBeanServer.invoke(JmxMBeanServer.java:801)
		at org.apache.catalina.mbeans.MBeanFactory.createStandardContext(MBeanFactory.java:460)
		at org.apache.catalina.mbeans.MBeanFactory.createStandardContext(MBeanFactory.java:408)
		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.apache.tomcat.util.modeler.BaseModelMBean.invoke(BaseModelMBean.java:293)
		at com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.invoke(DefaultMBeanServerInterceptor.java:819)
		at com.sun.jmx.mbeanserver.JmxMBeanServer.invoke(JmxMBeanServer.java:801)
		at com.sun.jmx.remote.security.MBeanServerAccessController.invoke(MBeanServerAccessController.java:468)
		at javax.management.remote.rmi.RMIConnectionImpl.doOperation(RMIConnectionImpl.java:1468)
		at javax.management.remote.rmi.RMIConnectionImpl.access$300(RMIConnectionImpl.java:76)
		at javax.management.remote.rmi.RMIConnectionImpl$PrivilegedOperation.run(RMIConnectionImpl.java:1309)
		at java.security.AccessController.doPrivileged(Native Method)
		at javax.management.remote.rmi.RMIConnectionImpl.doPrivilegedOperation(RMIConnectionImpl.java:1408)
		at javax.management.remote.rmi.RMIConnectionImpl.invoke(RMIConnectionImpl.java:829)
		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 sun.rmi.server.UnicastServerRef.dispatch(UnicastServerRef.java:357)
		at sun.rmi.transport.Transport$1.run(Transport.java:200)
		at sun.rmi.transport.Transport$1.run(Transport.java:197)
		at java.security.AccessController.doPrivileged(Native Method)
		at sun.rmi.transport.Transport.serviceCall(Transport.java:196)
		at sun.rmi.transport.tcp.TCPTransport.handleMessages(TCPTransport.java:573)
		at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(TCPTransport.java:834)
		at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.lambda$run$0(TCPTransport.java:688)
		at java.security.AccessController.doPrivileged(Native Method)
		at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(TCPTransport.java:687)
		at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
		at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
		at java.lang.Thread.run(Thread.java:750)
	Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'org.springframework.http.converter.json.MappingJackson2HttpMessageConverter#42545a09': Lookup method resolution failed; nested exception is java.lang.IllegalStateException: Failed to introspect Class [org.springframework.http.converter.json.MappingJackson2HttpMessageConverter] from ClassLoader [ParallelWebappClassLoader
  context: MVC12_Web_exploded
  delegate: false
----------> Parent Classloader:
java.net.URLClassLoader@123772c4
]

大概报错就是这种的，只能复制这么多，具体原因是因为打包的工程内没有你pom新添加的依赖jar包

例如我这里pom依赖了fastjson的三个jar包，但是没有添加到打包的工程内

 可以看到没有对应的jar包，直接在这个地方导入jar包就行了

这个地方直接全选，idea会自动将不存在lib目录下的jar包添加进去，如果你没有lib目录先在该界面web-inf目录下新建一个，将依赖的jar包放到这个文件夹内