No converter found for return value of type

在controller中返回对象要注意以下几点：
1.entity对象要写上get/set方法
2.要导入json的包：

<properties>
    <jackson.version>2.5.4</jackson.version>
  </properties> 

  <dependency>
      <groupId>com.fasterxml.jackson.core</groupId>
      <artifactId>jackson-core</artifactId>
      <version>${jackson.version}</version>
    </dependency>
    <dependency>
      <groupId>com.fasterxml.jackson.core</groupId>
      <artifactId>jackson-databind</artifactId>
      <version>${jackson.version}</version>
    </dependency>