?这是博主的javaEE踩坑笔记专栏，希望遇到的问题可以积少成多，纪录的问题越多，能解决的问题也就越多，也希望我遇到的问题可以帮助到在看这篇文章的读者朋友们。 ?也是有一段时间没记录问题了，这次暑假打算先改进一下之前写的一个小项目，在此之前先温习了一下书本上的内容。之前项目中的JSON交互我们使用的是阿里巴巴的fastjson，原来spring也有自己处理json格式数据请求的实现类。只不过需要引入三个Jackson的开源包。 ?jackson-annotations-2.8.8.jar : JSON转换注解包 ?jackson-core-2.8.8.jar ： JSON转换核心包 ?jackson-databind-2.8.8.jar ： JSON转换的数据核心包 ?三个核心包官网下载地址
?测试JSON数据交互时，出现了问题。 ?前端使用ajax发送JSON格式数据给后端。
<script type="text/javascript"> function testJSON() { //获取输入的用户名和密码 var username = $("#username").val(); var password = $("#password").val(); console.log("username=" + username) $.ajax({ url:"${pageContext.request.contextPath}/testJSON", type:"post", //data表示发送的数据 data:JSON.stringify({username:username,password:password}), //定义发送请求的数据格式为JSON字符串 contentType:"application/json;charset=UTF-8", //定义回调响应的数据格式为JSON字符串，该属性可省略 dataType:"json", //成功相应的结果 success:function (data) { if (data != null){ alert("您输入的用户名为：" + data.username + "密码为：" + data.password) }else{ alert("交互失败！") } } }); } </script>?点击按钮提交数据后报错，小伙伴们看看你们和博主是不是一样的报错：
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter': Instantiation of bean failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter]: Constructor threw exception; nested exception is java.lang.NoClassDefFoundError: Could not initialize class com.fasterxml.jackson.databind.ObjectMapper at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:1155) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1099) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:513) 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.web.servlet.FrameworkServlet.configureAndRefreshWebApplicationContext(FrameworkServlet.java:668) at org.springframework.web.servlet.FrameworkServlet.createWebApplicationContext(FrameworkServlet.java:634) at org.springframework.web.servlet.FrameworkServlet.createWebApplicationContext(FrameworkServlet.java:682) at org.springframework.web.servlet.FrameworkServlet.initWebApplicationContext(FrameworkServlet.java:553) at org.springframework.web.servlet.FrameworkServlet.initServletBean(FrameworkServlet.java:494) at org.springframework.web.servlet.HttpServletBean.init(HttpServletBean.java:171) at javax.servlet.GenericServlet.init(GenericServlet.java:158) at org.apache.catalina.core.StandardWrapper.initServlet(StandardWrapper.java:1134) at org.apache.catalina.core.StandardWrapper.loadServlet(StandardWrapper.java:1089) at org.apache.catalina.core.StandardWrapper.allocate(StandardWrapper.java:761) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:135) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:97) at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:542) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:143) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:687) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:78) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:346) at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:374) at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:887) at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1684) at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) at java.lang.Thread.run(Thread.java:748) Caused by: org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter]: Constructor threw exception; nested exception is java.lang.NoClassDefFoundError: Could not initialize class com.fasterxml.jackson.databind.ObjectMapper at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:154) at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:89) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:1147) ... 37 more Caused by: java.lang.NoClassDefFoundError: Could not initialize class com.fasterxml.jackson.databind.ObjectMapper at org.springframework.http.converter.json.Jackson2ObjectMapperBuilder.build(Jackson2ObjectMapperBuilder.java:588) at org.springframework.http.converter.json.MappingJackson2HttpMessageConverter.<init>(MappingJackson2HttpMessageConverter.java:57) at org.springframework.http.converter.support.AllEncompassingFormHttpMessageConverter.<init>(AllEncompassingFormHttpMessageConverter.java:66) at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.<init>(RequestMappingHandlerAdapter.java:182) at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) at java.lang.reflect.Constructor.newInstance(Constructor.java:423) at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:142) ... 39 more?查阅资料，说是jackson依赖版本的问题，或是jar文件版本不匹配。查看发现我引用的jar文件版本确实不同(有被自己蠢到…)。
<!--JSON转换的数据核心包--> <!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-databind --> <dependency> <groupId>com.fasterxml.jackson.core</groupId> <artifactId>jackson-databind</artifactId> <version>2.13.0-rc1</version> </dependency> <!--JSON转换核心包--> <!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-core --> <dependency> <groupId>com.fasterxml.jackson.core</groupId> <artifactId>jackson-core</artifactId> <version>2.8.8</version> </dependency> <!--JSON转换注解包--> <!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-annotations --> <dependency> <groupId>com.fasterxml.jackson.core</groupId> <artifactId>jackson-annotations</artifactId> <version>2.8.8</version> </dependency>?因为是从官网拷贝的，jackson-databind版本没改成匹配的。 改成下面这样就好了，最主要的是三个jar包的版本要相同。
<!--JSON转换的数据核心包--> <!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-databind --> <dependency> <groupId>com.fasterxml.jackson.core</groupId> <artifactId>jackson-databind</artifactId> <version>2.8.8</version> </dependency> <!--JSON转换核心包--> <!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-core --> <dependency> <groupId>com.fasterxml.jackson.core</groupId> <artifactId>jackson-core</artifactId> <version>2.8.8</version> </dependency> <!--JSON转换注解包--> <!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-annotations --> <dependency> <groupId>com.fasterxml.jackson.core</groupId> <artifactId>jackson-annotations</artifactId> <version>2.8.8</version> </dependency>?不说了，书还没看完呢(手动狗头)。
千里崎岖不辞苦，
仗剑江湖为红颜
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