JSON array string to JSONArray Object in Java

Question

I'm new to JSON manipulation in Java and I have a String in the form of a JSON Array with several layers I need to access and put into class attributes. For example, here's my JSON object:

{"JsonObject" : [{"attributeOne":"valueOne",
                  "attributeTwo":"valueTwo",
                  "attributeThree":[{"subAttributeOne":"subValueOne",
                                     "subAttributeTwo":"subValueTwo"}],
                  "attributeFour":[{"subAttributeOne":"subValueThree",
                                    "subAttributeTwo":"subValueFour"}],
                  "attributeFive":"valueThree"},
                 {"attributeOne":"valueFour",
                  "attributeTwo":"valueFive",
                  "attributeThree":[{"subAttributeOne":"subValueFive",
                                     "subAttributeTwo":"subValueSix"}],
                  "attributeFour":[{"subAttributeOne":"subValueSeven",
                                    "subAttributeTwo":"subValueEight"}],
                  "attributeFive":"valueSix"}]}

Lets say I have a class called MyClass that has these attributes, how would i parse this string, knowing this is an array of n Objects, each containing "attributeOne, attributeTwo, ..., attributeFive"?

Here's what I have so far:

public MyClass[] jsonToJava (String jsonObj)
{
    ArrayList<MyClass> myClassArray = new ArrayList<MyClass>();


    //Somehow create a JSONArray from my jsonObj String
    JSONArray jsonArr = new JSONArray(jsonObj); //Don't know if this would be correct

    for(int i=0; i<jsonArr.length; i++){
        MyClass myClassObject = new MyClass();
        myClassObject.setAttributeOne = jsonArr[i].getString("attributeOne");
        // How can I access the subAttributeOne and Two under attributeThree and Four?
        // add all other values to myClassObject
        myClassArray.add(myClassObject);
    }
    return myClassArray;
}

As you can probably tell, I'm fairly new to programming :P Thanks in advance for the help!

Answer 1

Try Jackson JSON:

ObjectMapper mapper = new ObjectMapper(); // can reuse, share globally
User user = mapper.readValue(jsonObj, User.class); //method overloaded to take String

grabbed this two liner from:

http://wiki.fasterxml.com/JacksonInFiveMinutes

http://jackson.codehaus.org/0.9.9/javadoc/org/codehaus/jackson/map/ObjectMapper.html

Should convert your JSON strong to an object. In a Java EE context you may be able to get this unmarshalling functionality at an endpoint with the appropriate annotation.

Answer 2

The way you are trying to do it is painful and involved.

I would suggest that you use a library like GSON and let it do the heavy lifting. http://code.google.com/p/google-gson/

The documentation has object examples: https://sites.google.com/site/gson/gson-user-guide#TOC-Object-Examples

Answer 3

For your example you can use recursion something like:

    public Object getChild(Object parent, int index) { 

    if (parent instanceof JSONArray) {          

        try {
            Object o =  ( (JSONArray)parent ).get(index);

            if( o instanceof JSONObject ){
                parent =  ((JSONObject) ( o ) ).getMap();                   
                return parent;
            }

            if( o instanceof Double ){
                parent =  (Double) o;                   
                return parent;
            }

            if( o instanceof Integer ){
                parent =  (Integer) o;                  
                return parent;
            }
                            ....


        } catch (JSONException e1) {
            e1.printStackTrace();
        }       
    }



    if (parent instanceof JSONObject) {             
        parent = ( (JSONObject)parent ).getMap();
    }

    if (parent instanceof Map<?, ?>) { 
        Map<?, ?> map = (Map<?, ?>) parent; 
        Iterator<?> it = map.keySet().iterator(); 
        for (int i=0; i<index; i++){
            it.next(); 
        }

        return map.get(it.next()); 
    }
    else if (parent instanceof Collection<?>) { 
        Iterator<?> it = ((Collection<?>) parent).iterator(); 

        for (int i=0; i<index; i++){
            it.next();              
        }
        return it.next(); 
    } 
    //throw new IndexOutOfBoundsException("'" + parent + "'cannot have children!"); 
    return null;
} 

But its a bit complicated (+bad practice to use instanceof) and you don't want to reinvent the wheel. So use GSON or Jackson.

 Gson gson =  new Gson();
 String myClassStr = gson.toGson(MyClassInstance);
 ....
  Myclass yourClass = gson.fromJson(myClassStr, Myclass.class);