FromJsonFunc.java

/**
 * 
 */
package org.archive.hadoop.pig.udf;

import java.io.IOException;
import java.util.Map;

import org.apache.pig.EvalFunc;
import org.apache.pig.data.Tuple;
import org.mortbay.util.ajax.JSON;

/**
 * A PIG function that translates JSON to Map object.
 * 
 * @author kenji
 */
public class FromJsonFunc extends EvalFunc<Map<String, Object>> {

	public FromJsonFunc() {
	}

	/* (non-Javadoc)
	 * @see org.apache.pig.EvalFunc#exec(org.apache.pig.data.Tuple)
	 */
	@SuppressWarnings("unchecked")
	@Override
	public Map<String, Object> exec(Tuple input) throws IOException {
		if (input.size() != 1)
			throw new IllegalArgumentException("expects exactly one String argument");
		String value = (String)input.get(0);
		if (value == null) return null;
		try {
			Object obj = JSON.parse(value);
			if (obj instanceof Map) {
				Map<?, ?> asmap = (Map<?, ?>)obj;
				for (Object k : asmap.keySet()) {
					if (!(k instanceof String)) {
						asmap.remove(k);
					}
				}
				return (Map<String, Object>)asmap;
			} else {
				throw new IOException("JSON '" + value + "' cannot be parsed into a Map");
			}
		} catch (IllegalStateException ex) {
			// JSON.parse() throws IllegalStateException for syntactical errors.
			// translate it into IOException.
			throw new IOException("failed to parse as JSON:" + value);
		}
	}

}