Convert nested java objects to Jackson JSON

问题:

Could someone provide an example or reference that provides a way to convert a nest JAVA object to JSON output using Jackson libraries preferably. I have no problem converting a flat JAVA object. However the JSON libraries show the nested object name and type rather than its sub-objects. I'm pretty much leveraging the same code provided here http://www.mkyong.com/java/jackson-2-convert-java-object-to-from-json/ . So I'm not attaching any code example.

e.g.

// This is what I get
{
"fname":null,
"lname":null,
"addr":null
}


// This is what I need as output
{
"name":null,
"lname":null,
"addr":{
    street:"mull",
    "city":null,
    "zip":0
}
}

This the sample class objects:

import address;

public class id implements Serializable {
public String fname;
public String lname;
public address addr; 

} 

public class address implements Serializable {
public String street;
public String city; 
public int zip;
}

回答1:

Create a class Address.

public class Address {
    private String street;
    private String city; 
    private int zip;
    public String getStreet() {
        return street;
    }
    public void setStreet(String street) {
        this.street = street;
    }
    public String getCity() {
        return city;
    }
    public void setCity(String city) {
        this.city = city;
    }
    public int getZip() {
        return zip;
    }
    public void setZip(int zip) {
        this.zip = zip;
    }
}

Create a class Id.

 public class Id {
    private String fname;
    private String lname;
    private Address addr;
    public String getFname() {
        return fname;
    }
    public void setFname(String fname) {
        this.fname = fname;
    }
    public String getLname() {
        return lname;
    }
    public void setLname(String lname) {
        this.lname = lname;
    }
    public Address getAddr() {
        return addr;
    }
    public void setAddr(Address addr) {
        this.addr = addr;
    }
}

Main method:

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;

public class Test {
    public static void main(String[] args) {
        Address addressObj = new Address();
        addressObj.setCity("Chicago");
        addressObj.setStreet("Some Street");
        addressObj.setZip(12345);

        Id idObj = new Id();
        idObj.setAddr(addressObj);
        idObj.setFname("Test");
        idObj.setLname("Tester");

        ObjectMapper mapper = new ObjectMapper();

        //Object to JSON in String
        try {
            String jsonInString = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(idObj);
            System.out.println(jsonInString);
        } catch (JsonProcessingException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }       
    }
}

Output:

{
  "fname" : "Test",
  "lname" : "Tester",
  "addr" : {
    "street" : "Some Street",
    "city" : "Chicago",
    "zip" : 12345
  }
}

回答2:

you have not initialized anything in class "id" and that is why everything is null. if you create an object of address and assign it before you convert object to json, you will get the structure you want. something like following.

public static void main( String args[] ){
id i = new id();
address a = new address();
i.serAddress( a );
//do writeValueAsString here
}

NOTE: Follow proper naming for class and variables