Simple JSON-javabean mapping utility based on JAXB

JSONContentReader.java

package wangzx.util.json;

import java.io.IOException;

import javax.xml.transform.sax.SAXSource;

import net.sf.json.JSONArray;
import net.sf.json.JSONObject;

import org.xml.sax.ContentHandler;
import org.xml.sax.DTDHandler;
import org.xml.sax.EntityResolver;
import org.xml.sax.ErrorHandler;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;
import org.xml.sax.SAXNotRecognizedException;
import org.xml.sax.SAXNotSupportedException;
import org.xml.sax.XMLReader;
import org.xml.sax.helpers.AttributesImpl;

/**
 * JSONContentReader pipes a JSON input to a XML(SAXSource) output.
 * 
 * using JSONContentReader with JAXB Unmarshaller:
 * <code>
 * 		JSONObject json;		// your JSON value
 * 		JSONContentReader reader = new JSONContentReader(json);
 * 
 * 		Unmarshaller unmarshaller;	// your jaxb unmarshaller
 * 		JavaBean youBean = (JavaBean) unmarshaller.unmarshal(reader);
 * </code>
 * 
 * @see JSONContentWriter pipes a XML(SAXSource) input to a JSON output
 * 
 * @author waltwang
 */
public class JSONContentReader extends SAXSource {

	// the object can contains only 1 key as the xml root element
	private JSONObject json;
	
	class JsonXmlReader implements XMLReader {

		private EntityResolver entityResolver;
		private DTDHandler dtdHandler;
		private ContentHandler contentHandler;
		private ErrorHandler errorHandler;

		@Override
		public boolean getFeature(String name)
				throws SAXNotRecognizedException, SAXNotSupportedException {
			return false;
		}

		@Override
		public void setFeature(String name, boolean value)
				throws SAXNotRecognizedException, SAXNotSupportedException {
		}

		@Override
		public Object getProperty(String name)
				throws SAXNotRecognizedException, SAXNotSupportedException {
			return null;
		}

		@Override
		public void setProperty(String name, Object value)
				throws SAXNotRecognizedException, SAXNotSupportedException {
		}

		@Override
		public void setEntityResolver(EntityResolver resolver) {
			this.entityResolver = resolver;
		}

		@Override
		public EntityResolver getEntityResolver() {
			return entityResolver;
		}

		@Override
		public void setDTDHandler(DTDHandler handler) {
			this.dtdHandler = handler;			
		}

		@Override
		public DTDHandler getDTDHandler() {
			return dtdHandler;
		}

		@Override
		public void setContentHandler(ContentHandler handler) {
			this.contentHandler = handler;
		}

		@Override
		public ContentHandler getContentHandler() {
			return contentHandler;
		}

		@Override
		public void setErrorHandler(ErrorHandler handler) {
			this.errorHandler = handler;
		}

		@Override
		public ErrorHandler getErrorHandler() {
			return errorHandler;
		}

		@Override
		public void parse(InputSource input) throws IOException, SAXException {
						
			contentHandler.startDocument();
			
			for(Object key: json.keySet()) {
				if(key instanceof String){
					String sKey = (String) key;
					Object value = json.get(key);
										
					visitJSON(contentHandler, sKey, value);
					
					break;
				}
			}
						
			contentHandler.endDocument();
		}

		@Override
		public void parse(String systemId) throws IOException, SAXException {
			throw new RuntimeException("parse with systemId not supported");
		}
		
	}
	
	void visitJSON(ContentHandler ch, String key, Object value) throws SAXException {

		AttributesImpl emptyAttrs = new AttributesImpl();

		if(value != null && value instanceof JSONArray){
			JSONArray array = (JSONArray) value;
			
			for(int i = 0; i<array.size(); i++) {
				Object elem = array.get(i);
				visitJSON(ch, key, elem);
			}
			
			return;
		}

		ch.startElement(null, key, key, emptyAttrs);

		do {
			if(value == null) {
				break;
			}
			if(value instanceof String) {
				String str = (String) value;
				ch.characters(str.toCharArray(), 0, str.length());
				break;
			}
			
			if(value instanceof JSONObject) {
				JSONObject jso = (JSONObject) value;
				for(Object subKey: jso.keySet()){
					if(subKey instanceof String) {
						String subKeyStr = (String) subKey;
						visitJSON(ch, subKeyStr, jso.get(subKeyStr));
					}
				}
				break;
			}
			
			throw new AssertionError("Unknown json type:" + value.getClass());
			
		} while(false);
		

		ch.endElement(null, key, key);

	}

	public JSONContentReader(JSONObject jso){
		this.json = jso;
		super.setXMLReader(new JsonXmlReader());
	}
	
	
}

JSONContentWriter.java

package wangzx.util.json;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import net.sf.json.JSONArray;
import net.sf.json.JSONObject;

import org.xml.sax.Attributes;
import org.xml.sax.ContentHandler;
import org.xml.sax.Locator;
import org.xml.sax.SAXException;

/**
 * JSONContentWriter pipes a a XML(ContentHandler) input event to JSON output.
 * 
 * using JSONContentReader with JAXB marshaller:
 * <code>
 * 
 * 		Marshaller marshaller;	// your jaxb marshaller
 * 		JavaBean yourBean;	// your jaxb bean
 * 		
 * 		JSONContentWriter jsonWriter = new JSONContentWriter();
 * 		marshaller.marshal(yourBean, jsonWriter);
 * 		JSONObject json = jsonWriter.toJSON(); 
 * </code>
 * 
 * @see JSONContentWriter pipes a XML(SAXSource) input to a JSON output
 * 
 * @author waltwang
 */
public class JSONContentWriter implements ContentHandler {

	static class Node {
		Node parent;
		List<Node> children = new ArrayList<Node>();
		String name;	// either elementTagName or @attributeName
		String value;	// if no children
		
		public Object toJSON(){
			
			if(children.size()==0) 
				return (value == null) ? "" : value;
			
			Map<String, List<Node>> childsByName = new HashMap<String, List<Node>>();
			for(Node it: children) {
				if(childsByName.containsKey(it.name))
					childsByName.get(it.name).add(it);
				else {
					ArrayList<Node> nodes = new ArrayList<Node>();
					nodes.add(it);
					childsByName.put(it.name, nodes);
				}
			}
			
			JSONObject jso = new JSONObject();
			
			for(String key: childsByName.keySet()){
				List<Node> values = childsByName.get(key);
				if(values.size() == 1) { // { "key": value }
					jso.put(key, values.get(0).toJSON());
				}
				else {
					JSONArray jsarray = new JSONArray();
					for(Node it: values) jsarray.add(it.toJSON());
					jso.put(key, jsarray);
				}
			}
			
			return jso;
		}
	}
	
	Node root;
	Node current;

	@Override
	public void setDocumentLocator(Locator locator) {
		//System.out.println("setDocumentLocator:locator" + locator);
	}

	@Override
	public void startDocument() throws SAXException {
		root = new Node();
		current = root;
	}

	@Override
	public void endDocument() throws SAXException {
		//System.out.println("endDocument");		
	}

	@Override
	public void startPrefixMapping(String prefix, String uri)
			throws SAXException {
		//System.out.println("startPrefixMapping:prefix=" + prefix + ";uri=" + uri);		
	}

	@Override
	public void endPrefixMapping(String prefix) throws SAXException {
		//System.out.println("endPrefixMapping:" + prefix);			
	}

	@Override
	public void startElement(String uri, String localName, String qName,
			Attributes atts) throws SAXException {
		System.out.println("startElement: uri=" + uri + ";localName=" + localName + ";qName=" + qName);
		Node node = new Node();
		node.parent = current;
		node.name = localName;
		current.children.add(node);
		current = node;
	}

	@Override
	public void endElement(String uri, String localName, String qName)
			throws SAXException {
		System.out.println("endElement: uri=" + uri + ";localName=" + localName + ";qName=" + qName);
		current = current.parent;
	}

	@Override
	public void characters(char[] ch, int start, int length)
			throws SAXException {
		//System.out.println("characters:" + new String(ch, start, length));		
		if(current.value != null)
			current.value = current.value + new String(ch, start, length);
		else
			current.value = new String(ch, start, length);
	}

	@Override
	public void ignorableWhitespace(char[] ch, int start, int length)
			throws SAXException {
		//System.out.println("ignorableWhitespace:" + new String(ch, start, length));		
	}

	@Override
	public void processingInstruction(String target, String data)
			throws SAXException {
		//System.out.println("processingInstruction:target=" + target + ";data=" + data);		
		
	}

	@Override
	public void skippedEntity(String name) throws SAXException {
		//System.out.println("skippedEntity:name=" + name);		
		
	}
	
	public JSONObject toJSON() {
		// the root node is always a JSONObject
		return (JSONObject) root.toJSON();
	}

}

TestJson.java

package wangzx.util.json;

import java.util.ArrayList;
import java.util.List;

import javax.xml.bind.JAXBContext;
import javax.xml.bind.Marshaller;
import javax.xml.bind.Unmarshaller;
import javax.xml.bind.annotation.XmlAccessType;
import javax.xml.bind.annotation.XmlAccessorType;
import javax.xml.bind.annotation.XmlRootElement;

import net.sf.json.JSON;
import net.sf.json.JSONObject;
import net.sf.json.util.JSONTokener;

import org.junit.Assert;
import org.junit.Test;

public class TestJson {
	
	@XmlAccessorType(XmlAccessType.FIELD)
	static class Address {
		
		String addr1;
		String addr2;
		String postcode;
		
	}
	@XmlRootElement @XmlAccessorType(XmlAccessType.FIELD)
	static class Student {
		
		String name;
		int age;
		
		List<Address> address = new ArrayList<TestJson.Address>();
	}

	@Test
	public void testMarshal() throws Exception {
		
		Student student = new Student();
		student.name = "waltwang";
		student.age = 39;
		
		Address address1 = new Address();
		address1.addr1 = "addr1";
		address1.addr2 = "addr2";
		address1.postcode = "510000";

		Address address2 = new Address();
		address2.addr1 = "ADDR1";
		address2.addr2 = "ADDR2";
		address2.postcode = "510001";
		
		student.address.add(address1);
		student.address.add(address2);

		JAXBContext ctx = JAXBContext.newInstance(Student.class);
		Marshaller marshaller = ctx.createMarshaller();
		marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
		
		JSONContentWriter jsonWriter = new JSONContentWriter();
		
		marshaller.marshal(student, jsonWriter);
		
		JSON result = (JSON) jsonWriter.toJSON();

		System.out.println( result.toString() );
		
	}
	
	@Test
	public void testUnmarshal() throws Exception{
		
		String input = "{\"student\":{\"address\":[{\"addr1\":\"addr1\",\"addr2\":\"addr2\",\"postcode\":\"510000\"},{\"addr1\":\"ADDR1\",\"addr2\":\"ADDR2\",\"postcode\":\"510001\"}],\"age\":\"39\",\"name\":\"waltwang\"}}";
		
		JSONObject value = (JSONObject) new JSONTokener(input).nextValue();

		JAXBContext ctx = JAXBContext.newInstance(Student.class);
		Unmarshaller unmarshaller = ctx.createUnmarshaller();
		Marshaller marshaller = ctx.createMarshaller();
		marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
		
		JSONContentReader jsonReader = new JSONContentReader(value);
		
		Student student = (Student) unmarshaller.unmarshal(jsonReader);

		marshaller.marshal(student, System.out);
		
		Assert.assertEquals("waltwang", student.name);
	}

}