https://github.com/douglascrockford/JSON-java: JSON is a light-weight, language independent, data interchange format. See http://www.JSON.org/ The files in this package implement JSON encoders/decoders in Java. It also includes the capability to convert between JSON and XML, HTTP headers, Cookies, and CDL. This is a reference implementation. There is a large number of JSON packages in Java. Perhaps someday the Java community will standardize on one. Until then, choose carefully. The license includes this restriction: "The software shall be used for good, not evil." If your conscience cannot live with that, then choose a different package.
  • Douglas Crockford 
package org.json;

The JSONString interface allows a toJSONString()
method so that a class can change the behavior of
JSONObject.toString(), JSONArray.toString(),
and JSONWriter.value(Object). The
toJSONString method will be used instead of the default behavior
of using the Object's toString() method and quoting the result.

/**
 * The <code>JSONString</code> interface allows a <code>toJSONString()</code>
 * method so that a class can change the behavior of
 * <code>JSONObject.toString()</code>, <code>JSONArray.toString()</code>,
 * and <code>JSONWriter.value(</code>Object<code>)</code>. The
 * <code>toJSONString</code> method will be used instead of the default behavior
 * of using the Object's <code>toString()</code> method and quoting the result.
 */
public interface JSONString {
    
The toJSONString method allows a class to produce its own JSON
serialization.

Returns:A strictly syntactically correct JSON text.
/**
     * The <code>toJSONString</code> method allows a class to produce its own JSON
     * serialization.
     *
     * @return A strictly syntactically correct JSON text.
     */
    public String toJSONString();
}