json to java object custom parsers

Question

Are there any custom JSON to java object parsers to map json properties to Java object attributes through some configuration.

suppose I have class

class Person { String id; String name; String loc;}

My json String is

{name:"xy",id:12, address: {location: "abc"}}

I need map location.address of json to loc property of Person. We need to drive this mapping through config XML or prop file.

EDITED....

I am trying to have grammer or rules defined in property file such as:

address.location = loc
id = id
name = name

This is what I am thinking. Not sure how map complex types such as List, Map, etc

So my code would call a method

Person p = ObjectMapper.map(jsonData,Person.class,configuration)

and actual mapping is done is this way

class ObjectMapper {
public static <T> T map(String jsonData,Class<T> rootType, Map<String,String> rules) {

    T object = rootType.newInstance();
     // TODO: code to parse json using the rules 
     //and finally return object

    return (T) object;
}

This is what I am planning to do. Any help is appreciated. Thanks in Advance.

Answer 1

Use following code.

import java.lang.reflect.Method;
import java.lang.reflect.Type;
import java.util.HashMap;
import java.util.Map;

import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;

public class Test {

    public static void main(String... args) throws Exception{
        Map<String, String> rules = new HashMap<>();
        rules.put("address.location", "loc");
        rules.put("name", "name");
        rules.put("id", "id");

        String jsonData = "{name:'xy',id:'12', address: {location: 'abc'}, phones: ['a', 'b', 'c']}";

        Person person = (Person) map(jsonData, Person.class, rules);
        System.out.println(new Gson().toJson(person));
    }

    public static Object map(String jsonData, Class<?> rootType, Map<String, String> rules) throws Exception{
        Map<String, Object> genericMap = new HashMap<>();
        Type type = new TypeToken<Map<String, Object>>() {}.getType();
        genericMap = new Gson().fromJson(jsonData, type);

        Object object = rootType.newInstance();

        for (Map.Entry<String, String> entry : rules.entrySet()){
            String mapKey = entry.getKey();
            String mapValue = entry.getValue();

            String keys[] = mapKey.split("\\.");
            Map<String, Object> obj = null;
            if(keys.length > 1){
                obj = (Map<String, Object>) genericMap.get(keys[0]);
                for(int i=1;i<keys.length-1;i++){
                    obj = (Map<String, Object>) obj.get(keys[i]);
                }
                // Method method = object.getClass().getDeclaredMethod("set" +  capitalize(mapValue) , String.class);
                // method.invoke(object, (String)obj.get(keys[keys.length-1]));
                Field field = object.getClass().getDeclaredField(mapValue);
                field.set(object, obj.get(keys[keys.length - 1]));
            }else{
                // Method method = object.getClass().getDeclaredMethod("set" +  capitalize(mapValue) , String.class);
                // method.invoke(object, (String)genericMap.get(mapValue));

                Field field = object.getClass().getDeclaredField(mapValue);
                field.set(object, genericMap.get(mapValue));
            }
        }
        return object;
    }

    public static  String capitalize(String line){
      return Character.toUpperCase(line.charAt(0)) + line.substring(1);
    }
}

class Person {
    String id;
    String name;
    String loc;

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getLoc() {
        return loc;
    }

    public void setLoc(String loc) {
        this.loc = loc;
    }

}

Output

{"id":"12","name":"xy","loc":"abc","phones":["a","b","c"]}

Details

• Used Gson API.
• This code works for n number referenced object (like a.b.c.item).
• Your class should contain getter/setter for each field.
• Field name of Rules and POJO should match.

Answer 2

Import this library to your project code.google.com/p/google-gson

Afterwards, it is possible to do this: ("json" is whatever json-String you want to parse in. It could be the one you specified in your question.)

Person personFromJson = new Gson().fromJson(json, Person.class);