出现问题简述：
使用jackson包 返回json字符串，出现报错java.lang.NoClassDefFoundError: com/fasterxml/jackson/databind/exc/InvalidDefinitionException，这里是因为jackson包和spring核心包版本不兼容出现的问题，
百度了一下网上说什么spring5.0.0的要用jackson2.7.5以上的包，但是我5.0.2spring配合2.8.8jackson包报错，我尝试了2.7.5 2.9.x 2.8.x都不行，

最终解决方案：
最后4.3.7spring配2.8.8jackson包就可以了

properties

<properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <maven.compiler.source>1.8</maven.compiler.source>
    <maven.compiler.target>1.8</maven.compiler.target>
    <spring.version>4.3.7.RELEASE</spring.version>    <!-- 下面的框架版本引用这里的几个version所用的版本-->
    <slf4j.version>1.6.6</slf4j.version>
    <log4j.version>1.2.12</log4j.version>
    <mysql.version>8.0.12</mysql.version>
    <mybatis.version>3.4.5</mybatis.version>
  </properties>

jackson包

<!-- 返回json字符串的支持 ，这里5.0.0spring包会不兼容，要使用4.3.7 -->
    <!-- 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>

spring包

 <!-- spring -->
    <dependency>
      <groupId>org.aspectj</groupId>
      <artifactId>aspectjweaver</artifactId>
      <version>1.6.8</version>
    </dependency>



    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-context</artifactId>
      <version>${spring.version}</version>
    </dependency>
    <!--下面两个springmvc-->
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-web</artifactId>
      <version>${spring.version}</version>
    </dependency>

    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-webmvc</artifactId>
      <version>${spring.version}</version>
    </dependency>
    <!--单元测试-->
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-test</artifactId>
      <version>${spring.version}</version>
    </dependency>
    <!--事务-->
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-tx</artifactId>
      <version>${spring.version}</version>
    </dependency>
    <!--jdbc模板技术-->
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-jdbc</artifactId>
      <version>${spring.version}</version>
    </dependency>