Json - Java Object to Json

Question

I am very new to Json and my goal to create the Json output below from Java bean. How should I structure my Java object? Should I have MyResult class and User and Result as

Answer 1

What Json library can I use for this? Jackson Library is used to serialize Java objects into JSON and deserialize JSON string into Java objects. Add the following dependencies to pom.xml.

   <dependency>
     <groupId>com.fasterxml.jackson.core</groupId>
     <artifactId>jackson-databind</artifactId>
     <version>2.9.4</version> 
     </dependency>

This dependency will transitively add the following libraries to the classpath: jackson-annotations-2.9.4.jar jackson-core-2.9.4.jar jackson-databind-2.9.4.jar

**Note: Please always go with the latest jars.

How should I structure my Java object? Please see the full working code.

  **MainClass.java:**

      import java.io.IOException;

     import com.fasterxml.jackson.databind.ObjectMapper;
     import com.fasterxml.jackson.databind.SerializationFeature;

    public class MainClass {

    public static void main(String[] args) throws IOException {

    ObjectMapper mapper = new ObjectMapper();
    mapper.enable(SerializationFeature.INDENT_OUTPUT);

    Result result = new Result();
    result.setCourse("blah");
    result.setScore("10.0");

    User user = new User();
    user.setName("blah blah");
    user.setEmail("blah@blah.com");

    MyResult myResult = new MyResult();
    myResult.setAccountID("12345");
    myResult.setResult(result);
    myResult.setUser(user);

    MyPojo myPojo = new MyPojo();
    myPojo.setMyResult(myResult);

    String jsonStr = mapper.writeValueAsString(myPojo);

    System.out.println(jsonStr);

} }

     **MyPojo.java:-**


    import com.fasterxml.jackson.annotation.JsonProperty;
    import com.fasterxml.jackson.annotation.JsonPropertyOrder;

@JsonPropertyOrder({ "AccountID", "User", "Result" })
public class MyPojo {
private MyResult MyResult;

public MyResult getMyResult() {
    return MyResult;
}

@JsonProperty("MyResult")
public void setMyResult(MyResult MyResult) {
    this.MyResult = MyResult;
} }


    **MyResult.java:**

import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.annotation.JsonPropertyOrder;

@JsonPropertyOrder({ "AccountID", "User", "Result" })
public class MyResult {

private User User;

private Result Result;

private String AccountID;

public User getUser() {
    return User;
}

@JsonProperty("User")
public void setUser(User User) {
    this.User = User;
}

public Result getResult() {
    return Result;
}

@JsonProperty("Result")
public void setResult(Result Result) {
    this.Result = Result;
}

public String getAccountID() {
    return AccountID;
}

  @JsonProperty("AccountID")
  public void setAccountID(String AccountID) {
    this.AccountID = AccountID;
    } }


    **Result.java:**

 import com.fasterxml.jackson.annotation.JsonProperty;
 import com.fasterxml.jackson.annotation.JsonPropertyOrder;

   @JsonPropertyOrder({ "Course", "Score" })
    public class Result {

    private String Course;

    private String Score;

    public String getCourse() {
    return Course;
    }

    @JsonProperty("Course")
    public void setCourse(String Course) {
    this.Course = Course;
}

   public String getScore() {
    return Score;
}

   @JsonProperty("Score")
  public void setScore(String Score) {
    this.Score = Score;
  } }


    **User.java:**

    import com.fasterxml.jackson.annotation.JsonProperty;
    import com.fasterxml.jackson.annotation.JsonPropertyOrder;

    @JsonPropertyOrder({ "Name", "Email" })
      public class User {

    private String Name;

    private String Email;

    public String getName() {
    return Name;
    }

@JsonProperty("Name")
public void setName(String Name) {
    this.Name = Name;
}

public String getEmail() {
    return Email;
}

@JsonProperty("Email")
public void setEmail(String Email) {
    this.Email = Email;
}

@Override
public String toString() {
    return "ClassPojo [Name = " + Name + ", Email = " + Email + "]";
} }

   **Result:**

      {
  "MyResult" : {
    "AccountID" : "12345",
   "User" : {
     "Name" : "blah blah",
     "Email" : "blah@blah.com"
   },
   "Result" : {
     "Course" : "blah",
     "Score" : "10.0"
   }
  }
}

Note: Please note the use of Json Annotations like @JsonProperty("Email") to make json property names as same in the expected output & @JsonPropertyOrder({ "Name", "Email" } to maintain the sequence as in expected output. Refer: https://www.baeldung.com/jackson-annotations.

Answer 2

Although closed, this SO post can help you understand the differences between Jackson and GSON. Which one is "best" depends on what is important for you.

EDIT: Specifically for Jackson, your example looks a lot like the example they give for what they call Full Data Binding, you can read it here. Btw, although the announced 5 minutes needed to read that document is maybe a bit short, it gives a complete overview of the different ways Jackson can be used. You'll also notice that the examples given do not use annotations.

Answer 3

Googles GSON is a really nice json lib. This is from the previous link and it basically outlines some of its functionality.

Answer 4

Note: I'm the EclipseLink JAXB (MOXy) lead and a member of the JAXB (JSR-222) expert group.

---

How should I structure my Java object?

Below is what your object model could look like. MOXy's JSON binding leverages JAXB annotations for mapping the domain model to JSON, so I have included those as well. JAXB implementations have default rules for mapping field/property names, but since your document differs from the default each field had to be annotated.

MyResult

package forum11001458;

import javax.xml.bind.annotation.*;

@XmlRootElement(name="MyResult")
public class MyResult {

    @XmlElement(name="AccountID")
    private String accountID;

    @XmlElement(name="User")
    private User user;

    @XmlElement(name="Result")
    private Result result;

}

User

package forum11001458;

import javax.xml.bind.annotation.XmlElement;

public class User {

    @XmlElement(name="Name")
    private String name;

    @XmlElement(name="Email")
    private String email;

}

Result

package forum11001458;

import javax.xml.bind.annotation.XmlElement;

public class Result {

    @XmlElement(name="Course")
    private String course;

    @XmlElement(name="Score")
    private String score;

}

---

What Json library can I use for this?

Below is how you can use MOXy to do the JSON binding:

jaxb.properties

To use MOXy as your JAXB provider you need to include a file called jaxb.properties with the following entry in the same package as your domain model:

javax.xml.bind.context.factory=org.eclipse.persistence.jaxb.JAXBContextFactory

Demo

Note how MOXy's JSON binding does not require any compile time dependencies. All the necessary APIs are available in Java SE 6. You can add the necessary supporting APIs if you are using Java SE 5.

package forum11001458;

import java.io.File;
import javax.xml.bind.*;

public class Demo {

    public static void main(String[] args) throws Exception {
        JAXBContext jc = JAXBContext.newInstance(MyResult.class);

        Unmarshaller unmarshaller = jc.createUnmarshaller();
        unmarshaller.setProperty("eclipselink.media-type", "application/json");
        File json = new File("src/forum11001458/input.json");
        Object myResult = unmarshaller.unmarshal(json);

        Marshaller marshaller = jc.createMarshaller();
        marshaller.setProperty("eclipselink.media-type", "application/json");
        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
        marshaller.marshal(myResult, System.out);
    }

}

input.json/Output

{
   "MyResult" : {
      "AccountID" : "12345",
      "User" : {
         "Name" : "blah blah",
         "Email" : "blah@blah.com"
      },
      "Result" : {
         "Course" : "blah",
         "Score" : "10.0"
      }
   }
}

Answer 5

Or GSON

Super easy (no getters/settres, no annotations or configurations needed).

class BagOfPrimitives {
  private int value1 = 1;
  private String value2 = "abc";
  private transient int value3 = 3;
}

BagOfPrimitives obj = new BagOfPrimitives();
Gson gson = new Gson();
String json = gson.toJson(obj); 

==> json is {"value1":1,"value2":"abc"}

Answer 6

jackson is also pretty fast and easy to use