SpringMVC: spring mvc No converter found for return value of type: class

一、检查是否加了jackson依赖：

<dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-core</artifactId>
            <version>2.14.1</version>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.14.1</version>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-annotations</artifactId>
            <version>2.14.1</version>
        </dependency>

二、是否通过xml或注解配置了如下bean:

<mvc:annotation-driven>
        <mvc:message-converters>
            <bean class="org.springframework.http.converter.StringHttpMessageConverter"/>
            <bean class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter"/>
        </mvc:message-converters>
    </mvc:annotation-driven>