406错误：

原因：后端返回数据，但是前端无法正常接收数据

情况：cotroller上加注解 @RestController 默认返回前端的数据是json格式，但返回的不是json，所以出现了406错误

解决方案：

方案1：

使用json转换jar，如fastJSON...将数据转换成JSON格式 

方案2：

springMVC中有内置的消息转换类，但未完全导入依赖，所以：（导入如下依赖即可）

<!--解决返回视图层406错误的jar包 start-->
<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-core</artifactId>
    <version>2.11.0</version>
</dependency>
<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.11.0</version>
</dependency>
<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-annotations</artifactId>
    <version>2.11.0</version>
</dependency>
<!--解决返回视图层406错误的jar包 end-->

方案2需要注意的问题：

如果你的spring版本在5.0以上，jackson的版本至少在2.9以上！

否则就是以下错误：

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': 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: com/fasterxml/jackson/databind/exc/InvalidDefinitionException
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': 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: com/fasterxml/jackson/databind/exc/InvalidDefinitionException