1.检查是否加了jackson包
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-core</artifactId>
<version>2.0.1</version>
</dependency>
<!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-databind -->
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-databind</artifactId>
<version>2.0.1</version>
</dependency>
2.检查配置文件是否缺少
<mvc:annotation-driven/>
<mvc:default-servlet-handler/>