Java, JSON and reflection

Posted on 2008-10-09
Last Modified: 2013-12-22
Hy all

I playing a little with Java and Reflection.

So the Idea is to transform a Java object in a JSON object.

For now seems that works if I have a class just with public fields. But if I have package fields, they aren't collectable like this. How to get them?

Note: I will say thanks if you get me a Lib doing this, but I prefer to do it myself.

package oleber.json.simple;
import java.lang.reflect.Field;
import java.util.Collection;
import java.util.Map;
public class JSONable implements IJSONable {
	public JSONObject toJSON() {
		try {
			JSONObject objJSON = new JSONObject();
			JSONObject objValues = new JSONObject();
			JSONObject objTypes = new JSONObject();
			objJSON.put("values", objValues);
			objJSON.put("types", objTypes);
			for ( Field field : getClass().getFields() ) {
				if ( field.getType() == byte.class ) {
					objValues.put(field.getName(), field.getByte(this));
				} else if ( field.getType() == char.class ) {
					objValues.put(field.getName(), field.getChar(this));
				} else if ( field.getType() == short.class ) {
					objValues.put(field.getName(), field.getShort(this));
				} else if ( field.getType() == int.class ) {
					objValues.put(field.getName(), field.getInt(this));
				} else if ( field.getType() == long.class ) {
					objValues.put(field.getName(), field.getLong(this));
				} else if ( field.getType() == float.class ) {
					objValues.put(field.getName(), field.getFloat(this));
				} else if ( field.getType() == double.class ) {
					objValues.put(field.getName(), field.getDouble(this));
				} else if ( field.getType() == boolean.class ) {
					objValues.put(field.getName(), field.getBoolean(this));
				} else if ( field.getType() == String.class ) {
					objValues.put(field.getName(), field.get(this));
				} else {
					Object value = field.get(this);
					if ( value == null ) {
						objValues.put(field.getName(), null);
					} else if ( value instanceof String || value instanceof IJSONable) {
						objValues.put(field.getName(), value);
						objTypes.put(field.getName(), value.getClass().toString());
					} else if ( value instanceof Collection ) {
						JSONArray array = new JSONArray( ( Collection<?> ) value );
						objValues.put(field.getName(), array);
						objTypes.put(field.getName(), value.getClass().toString());
					} else if ( value instanceof Map ) {
						JSONObject object = new JSONObject( ( Map<String,?> ) value );
						objValues.put(field.getName(), object);
						objTypes.put(field.getName(), value.getClass().toString());
			return objJSON;
		} catch ( Exception e ) {
			return null;
	public JSONable toJSON(JSONObject obj) {
		return null;
	public String toString() {
		return toJSON().toString();

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Question by:oleber
  • 5
  • 2

Expert Comment

ID: 22676503
Try the following. This will return an array of all fields of the class, including package, private, protected and public fields.
for ( Field field : getClass().getDeclaredFields() ) {

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Expert Comment

ID: 22676527
hmm. ignore it. with this code snippet you get the fields but you can't access them from another package.
With field.isAccessible() you can check the accessibility of the field. If this field has default access only, you will get an error:
java.lang.IllegalAccessException: Class reflectiontest.Main can not access a member of class with modifiers ""
        at sun.reflect.Reflection.ensureMemberAccess(
LVL 10

Author Comment

ID: 22676562
that is my problem ;)

But you serialize a class, Where is the secret?
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Expert Comment

ID: 22676639
Do you know the structure of the classes?

Can't you access the package variables from the get methods?
LVL 10

Author Comment

ID: 22676690
I'm trying to do this generic. Basically every child class from this would be able of convert itself to JSON.

Expert Comment

ID: 22676735

Accepted Solution

manuel_m earned 500 total points
ID: 22676748

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