Read/write POJO in Database as JSON string

Question

I am searching on this problem for two days now, without a proper solution.

I have a PostgreSQL-Database with a table:

CREATE TABLE mytable (key text PRIMARY KEY, content text)

Further, I have a Java SpringBoot-Application with a JPA entity class:

@Entity
@Table(name = "mytable")
public class MyEntity {

  @Id
  private String key;

  // tell JPA to convert MyPojo to JSON using the default Jackson ObjectMapper
  private MyPojo content;

  // constructors, getters, setters

}

The MyPojo class contains sub-structure involving basic types, Maps, Lists, and other nested POJO classes. It does not seem convenient to write a Converter for the MyPojo class and all the other nested POJO classes. Instead, I want to use Jackson to serialize/deserialize it.

How do I configure Jackson/JPA to store a MyPojo object as a JSON string in the text field of the database table? I was hoping for a suitable Annotation like @Convert(converter=Jackson.ObjectMapper). Introducing an additional String field to the MyEntity class was another approach that would not work.

I sucessfully used Jackson to send/parse MyPojo objects as JSON strings to a REST interface, but I'm struggling to put the same string into the text field of a database.

David SN · Accepted Answer · 2018-03-28 14:40:51Z

3

You could define a converter to convert between the Pojo and JSON and use Jackson to make the conversion:

@Converter
public class MyPojoToJsonConverter implements AttributeConverter<MyPojo, String>{

    ObjectMapper objectMapper = new ObjectMapper();

    @Override
    public String convertToDatabaseColumn(MyPojo myPojo) {
        String json = "";
        try {
            json = objectMapper.writeValueAsString(myPojo);
        } catch (JsonProcessingException jpe) {
            // Handle exception
        }
        return json;
    }

    @Override
    public MyPojo convertToEntityAttribute(String myPojoAsJson) {
        MyPojo myPojo = null;
        try {
            myPojo = objectMapper.readValue(myPojoAsJson, MyPojo.class);
        } catch (JsonParseException e) {
            // HandleException
        } catch (JsonMappingException e) {
            // HandleException
        } catch (IOException e) {
            // HandleException
        }
        return myPojo;
    }
}

Then you can setup this converter in the attribute of your Entity using the @Convert annotation:

@Entity
@Table(name = "mytable")
public class MyEntity {

    @Id
    private String key;

    @Convert(converter=MyPojoToJsonConverter.class)
    private MyPojo content;
}

answered Mar 28, 2018 at 14:40

David SN

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1 Comment

Max Over a year ago

Thanks a lot. This approach works quite well. I can write a single Converter class, and all substructures in the POJO are (de)serialized automatically.

Lord_Pinhead · Accepted Answer · 2018-03-28 12:43:23Z

0

MyPojo should the a String not an Object in your Entity. Put your JSON in the String, that should be all.

answered Mar 28, 2018 at 12:43

Lord_Pinhead

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1 Comment

Max Over a year ago

I could do that. But how do I obtain a MyPojo object from this on the fly?

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