Unique.java

package org.supercsv.cellprocessor.constraint;

import java.util.HashSet;

import org.supercsv.cellprocessor.CellProcessorAdaptor;
import org.supercsv.cellprocessor.ift.CellProcessor;
import org.supercsv.exception.SuperCSVException;
import org.supercsv.util.CSVContext;

/**
 * Ensure that upon processing a CSV file (reading or writing), that values of the column all are unique. Comparison is
 * based upon each elements <tt>equals()</tt> method of the objects and lookup takes O(1).
 * <P>
 * Compared to {@link UniqueHashCode} this processor potentially uses more memory, as it stores references to each
 * encountered object rather than just their hashcodes. On reading huge files this can be a real memory-hazard, however,
 * it ensures a true uniqueness check.
 * 
 * @since 1.50
 * @author Kasper B. Graversen
 * @author Dominique De Vito
 */
public class Unique extends CellProcessorAdaptor {

protected HashSet<Object> previousEncounteredElements = new HashSet<Object>();

public Unique() {
	super();
}

public Unique(final CellProcessor next) {
	super(next);
}

/**
 * {@inheritDoc}
 * 
 * @throws SuperCSVException
 *             upon detecting a duplicate entry
 * @return the argument value if the value is unique
 */
@Override
public Object execute(final Object value, final CSVContext context) throws SuperCSVException {
	if( previousEncounteredElements.contains(value) ) {
		throw new SuperCSVException("Duplicate entry \"" + value + "\" error", context, this);
	} else {
		previousEncounteredElements.add(value);
	}
	
	// chaining
	return next.execute(value, context);
}
}