Convert a object into JSON in REST service by Spring MVC

Question

I m trying to create a REST service using Spring MVC and it s working if I m returning a plain string  My requirement is to return a JSON string of the Java object  Don t know how to achieve this by implicit conversion   Here is my code   StudentService java  package com spring schoolmanagement service   import java util List   import org springframework beans factory annotation Autowired  import org springframework stereotype Controller  import org springframework web bind annotation PathVariable  import org springframework web bind annotation RequestMapping  import org springframework web bind annotation RequestMethod  import org springframework web bind annotation ResponseBody   import com spring schoolmanagement dao CourseDAOImpl  import com spring schoolmanagement dao StateDAOImpl  import com spring schoolmanagement dao StudentDAOImpl  import com spring schoolmanagement model Student    Controller  RequestMapping   rest student   public class StudentService         Autowired     private CourseDAOImpl courseService       Autowired     private StudentDAOImpl studentService       Autowired     private StateDAOImpl stateService         RequestMapping value      id    method   RequestMethod GET  headers    Accept            ResponseBody     public Student home  PathVariable int id            return this studentService getById id               RequestMapping method   RequestMethod GET  headers    Accept            ResponseBody     public List lt Student gt  getAll   throws Exception           return this studentService getAll                RequestMapping value     test   method   RequestMethod GET  headers    Accept            ResponseBody     public String test             return  Test REST Service                Student java  package com spring schoolmanagement model   import java util Date   import javax validation constraints Size   import org hibernate validator constraints Email  import org hibernate validator constraints NotEmpty  import org springframework format annotation DateTimeFormat   public class Student extends Contact      private int id        NotEmpty      Size max   30      private String firstName  lastName        private String lastName        DateTimeFormat pattern  MM dd yyyy       private Date DOB  DOA        private Date DOA        NotEmpty      Email     private String email      private String password      private int courseID      private String courseName       public int getId             return id            public void setId int id            this id   id            public String getFirstName             return firstName            public void setFirstName String firstName            this firstName   firstName            public String getLastName             return lastName            public void setLastName String lastName            this lastName   lastName            public Date getDOB             return DOB            public void setDOB Date dOB            DOB   dOB            public Date getDOA             return DOA            public void setDOA Date dOA            DOA   dOA            public String getEmail             return email            public void setEmail String email            this email   email            public String getPassword             return password            public void setPassword String password            this password   password            public int getCourseID             return courseID            public void setCourseID int courseID            this courseID   courseID            public String getCourseName             return courseName            public void setCourseName String courseName            this courseName   courseName              Here http   localhost 8080 schoolmangement rest student test URL is returning  Test REST Service      But  http   localhost 8080 schoolmangement rest student 1 URL throwing HTTP Status code 406 with error message   The resource identified by this request is only capable of generating responses with characteristics not acceptable according to the request  accept  headers

User · Answer

The Json conversion should work out-of-the box. In order this to happen you need add some simple configurations:
First add a contentNegotiationManager into your spring config file. It is responsible for negotiating the response type:

<bean id="contentNegotiationManager"
      class="org.springframework.web.accept.ContentNegotiationManagerFactoryBean">
    <property name="favorPathExtension" value="false" />
    <property name="favorParameter" value="true" />
    <property name="ignoreAcceptHeader" value="true" />
    <property name="useJaf" value="false" />
     <property name="defaultContentType" value="application/json" />

      <property name="mediaTypes">
         <map>
            <entry key="json" value="application/json" />
            <entry key="xml" value="application/xml" />
         </map>
      </property>
   </bean>

   <mvc:annotation-driven
      content-negotiation-manager="contentNegotiationManager" />

   <context:annotation-config />

Then add Jackson2 jars (jackson-databind and jackson-core) in the service's class path. Jackson is responsible for the data serialization to JSON. Spring will detect these and initialize the MappingJackson2HttpMessageConverter automatically for you. Having only this configured I have my automatic conversion to JSON working. The described config has an additional benefit of giving you the possibility to serialize to XML if you set accept:application/xml header.

User · Answer

Spring framework itself handles json conversion when controller is annotated properly   For eg       PutMapping produces     application json             ResponseBody         public UpdateResponse someMethod      do something return UpdateResponseInstance      Here spring internally converts the UpdateResponse object to corresponding json string and returns it  In order to do it spring internally uses Jackson library   If you require a json representation of a model object anywhere apart from controller then you can use objectMapper provided by jackson  Model should be properly annotated for this to work   Eg   ObjectMapper mapper   new ObjectMapper    SomeModelClass someModelObject   someModelRepository findById idValue  get    mapper writeValueAsString someModelObject

User · Answer

Another simple solution is to add jackson-databind dependency in POM        lt dependency gt           lt groupId gt com fasterxml jackson core lt  groupId gt           lt artifactId gt jackson-databind lt  artifactId gt           lt version gt 2 8 1 lt  version gt       lt  dependency gt    Keep Rest of the code as it is

User · Answer

You can always add the  Produces  application json   above your web method or specify produces  application json  to return json  Then on top of the Student class you can add  XmlRootElement from javax xml bind annotation package   Please note  it might not be a good idea to directly return model classes  Just a suggestion   HTH

User · Answer

Finally I got solution using Jackson library along with Spring MVC  I got this solution from an example of Journal Dev  http   www journaldev com 2552 spring-restful-web-service-example-with-json-jackson-and-client-program     So  the code changes I have done are    Include the library in Maven  Add JSON conversion Servlet into servlet-context xml  Change the Model into Serializable    I didn t made any changes to my REST service controller  By default it converts into JSON

[java] Convert a object into JSON in REST service by Spring MVC

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