Data Hiding Using JsonIgnore and Spring Data JPA

Data hiding using JsonIgnore and Spring Data JPA is achieved using two approaches:

• @JsonIgnore and @JsonIgnoreProperties
• Repository Detection Strategies

This post considers @JsonIgnore and @JsonIgnoreProperties.

Code

The code is available at:

• https://github.com/farrelmr/introtospringdatarest/tree/4.0.0.
• https://github.com/farrelmr/introtospringdatarest/releases/tag/4.0.0.

Code Changes

I’ve added an extra table to for this example:

@Entity
public class Secrets {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private long id;
    private String mySecrets;
    public String getMySecrets() {
        return mySecrets;
    }
    public void setMySecrets(String mySecrets) {
        this.mySecrets = mySecrets;
    }
}

With its associated repository:

@PreAuthorize("hasRole('ROLE_USER')")
    public interface SecretsRepository extends CrudRepository<Secrets, Long> {
}

Running the Code

I have left the security from the last tutorial, Securing Spring Data REST with PreAuthorize, in place – but we can run this code using:

mvnw spring-boot:run

We can then call rest/profile to see the two exposed repositories:

curl - u user: user - X GET http: //localhost:8080/rest/profile
    {
        "_links": {
            "self": {
                "href": "http://localhost:8080/rest/profile"
            },
            "secrets": {
                "href": "http://localhost:8080/rest/profile/secrets"
            },
            "parkrunCourses": {
                "href": "http://localhost:8080/rest/profile/parkrunCourses"
            }
        }
    }

And calling the secrets REST endpoint:

curl - u user: user - X GET http: //localhost:8080/rest/secrets/1
    {
        "mySecret": "I want to hide this",
        "_links": {
            "self": {
                "href": "http://localhost:8080/rest/secrets/1"
            },
            "secret": {
                "href": "http://localhost:8080/rest/secrets/1"
            }
        }
    }

This post looks at techniques I can use to not expose the SecretRepository

@JsonIgnore and @JsonIgnoreProperties

The purpose of @JsonIgnore and @JsonIgnoreProperties is to hide attributes from the Jackson parser by instructing it to ignore these fields.

Usage is simply a matter of tagging the attribute with the @JsonIgnore.

@Entity
public class Secret {
    //
    @JsonIgnore
    private String mySecret;
    //
}

Or we can achieve the same using @JsonIgnoreProperties annotation:

curl - u user: user - X GET http: //localhost:8080/rest/secrets/1
    {
        "_links": {
            "self": {
                "href": "http://localhost:8080/rest/secrets/1"
            },
            "secret": {
                "href": "http://localhost:8080/rest/secrets/1"
            }
        }
    }

With either of these changes, we can then call our secrets REST endpoint, and the mySecret field is no longer exposed:

curl - u user: user - X GET http: //localhost:8080/rest/secrets/1
    {
        "_links": {
            "self": {
                "href": "http://localhost:8080/rest/secrets/1"
            },
            "secret": {
                "href": "http://localhost:8080/rest/secrets/1"
            }
        }
    }

Conclusion

@JsonIgnore or @JsonIgnoreProperties simply hides the field from the Jackson parser. This is good for hiding small pieces of information. The downside is we still have an exposed endpoint due to the default Repository Detection Strategies.