For the SO-13467258 question on http://stackoverflow.com/questions/13467258/reading-configuration-in-java-json-an-option

AbstractConfigPart.java

package com.sopovs.moradanen.gson;

public abstract class AbstractConfigPart implements ConfigElement {

  private boolean uniqueOnly;
	private int threshold;

	public AbstractConfigPart() {
	}

	public AbstractConfigPart(boolean uniqueOnly, int threshold) {
		this.uniqueOnly = uniqueOnly;
		this.threshold = threshold;
	}

	public boolean isUniqueOnly() {
		return uniqueOnly;
	}

	public void setUniqueOnly(boolean uniqueOnly) {
		this.uniqueOnly = uniqueOnly;
	}

	public int getThreshold() {
		return threshold;
	}

	public void setThreshold(int threshold) {
		this.threshold = threshold;
	}

	@Override
	public int hashCode() {
		final int prime = 31;
		int result = 1;
		result = prime * result + threshold;
		result = prime * result + (uniqueOnly ? 1231 : 1237);
		return result;
	}

	@Override
	public boolean equals(Object obj) {
		if (this == obj)
			return true;
		if (obj == null)
			return false;
		if (getClass() != obj.getClass())
			return false;
		AbstractConfigPart other = (AbstractConfigPart) obj;
		if (threshold != other.threshold)
			return false;
		if (uniqueOnly != other.uniqueOnly)
			return false;
		return true;
	}

}

CombinationOperation.java

package com.sopovs.moradanen.gson;

public enum CombinationOperation {
  AND, OR;
}

ConfigElement.java

package com.sopovs.moradanen.gson;

public interface ConfigElement {

}

ConfigParts.java

package com.sopovs.moradanen.gson;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;

public class ConfigParts implements ConfigElement {
  private CombinationOperation combOperation;
	private Collection<ConfigElement> elements;

	public ConfigParts() {
	}

	public ConfigParts(CombinationOperation combOperation, ConfigElement first, ConfigElement second,
			ConfigElement... otherElements) {
		this.combOperation = combOperation;
		elements = new ArrayList<ConfigElement>(otherElements.length + 2);
		elements.add(first);
		elements.add(second);
		elements.addAll(Arrays.asList(otherElements));
	}

	public CombinationOperation getCombOperation() {
		return combOperation;
	}

	public void setCombOperation(CombinationOperation combOperation) {
		this.combOperation = combOperation;
	}

	public Collection<ConfigElement> getElements() {
		return elements;
	}

	public void setElements(Collection<ConfigElement> elements) {
		if (elements.size() < 2) {
			throw new IllegalArgumentException();
		}
		this.elements = elements;
	}

	@Override
	public int hashCode() {
		final int prime = 31;
		int result = 1;
		result = prime * result + ((combOperation == null) ? 0 : combOperation.hashCode());
		result = prime * result + ((elements == null) ? 0 : elements.hashCode());
		return result;
	}

	@Override
	public boolean equals(Object obj) {
		if (this == obj)
			return true;
		if (obj == null)
			return false;
		if (getClass() != obj.getClass())
			return false;
		ConfigParts other = (ConfigParts) obj;
		if (combOperation != other.combOperation)
			return false;
		if (elements == null) {
			if (other.elements != null)
				return false;
		} else if (!elements.equals(other.elements))
			return false;
		return true;
	}

}

GsonTest.java

package com.sopovs.moradanen.gson;

import static com.sopovs.moradanen.gson.CombinationOperation.AND;
import static com.sopovs.moradanen.gson.CombinationOperation.OR;

import java.lang.reflect.Type;

import org.junit.Test;

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.JsonDeserializationContext;
import com.google.gson.JsonDeserializer;
import com.google.gson.JsonElement;
import com.google.gson.JsonObject;
import com.google.gson.JsonParseException;
import com.google.gson.JsonSerializationContext;
import com.google.gson.JsonSerializer;

public class GsonTest {
  @Test
	public void test() {
		Gson gson = new GsonBuilder()
				.setPrettyPrinting()
				.registerTypeAdapter(ConfigElement.class, new
						JsonDeserializer<ConfigElement>() {

							public ConfigElement deserialize(JsonElement json, Type
									typeOfT, JsonDeserializationContext context)
									throws JsonParseException {

								JsonObject jsonObject = json.getAsJsonObject();
								if (jsonObject.get("combOperation") != null) {
									return context.deserialize(json, ConfigParts.class);
								}
								if (jsonObject.get("keyWord") != null) {
									return context.deserialize(json, KeyWordConfigPart.class);
								}
								if (jsonObject.get("regex") != null) {
									return context.deserialize(json, RegexConfigPart.class);
								}
								throw new IllegalArgumentException();
							}
						})
				// This Serializer is needed only if Deserializer is specified
				.registerTypeAdapter(ConfigElement.class, new
						JsonSerializer<ConfigElement>() {
							public JsonElement serialize(ConfigElement src, Type typeOfSrc,
									JsonSerializationContext context) {
								return context.serialize(src, src.getClass());
							}
						})
				.create();

		ConfigElement config = new ConfigParts(OR, new ConfigParts(AND, new RegexConfigPart(false, 1, "^[a-zA-Z]*"),
				new KeyWordConfigPart(false, 5, "BarFoo")),
				new KeyWordConfigPart(true, 2, "FooBar"));

		String json = gson.toJson(config);

		System.out.println(json);
		System.out.println("Deserialization successful " + config.equals(gson.fromJson(json, ConfigElement.class)));
	}
}

KeyWordConfigPart.java

package com.sopovs.moradanen.gson;

public class KeyWordConfigPart extends AbstractConfigPart {

  private String keyWord;

	public KeyWordConfigPart() {
	}

	public KeyWordConfigPart(boolean uniqueOnly, int threshold, String keyWord) {
		super(uniqueOnly, threshold);
		this.keyWord = keyWord;
	}

	public String getKeyWord() {
		return keyWord;
	}

	public void setKeyWord(String keyWord) {
		this.keyWord = keyWord;
	}

	@Override
	public int hashCode() {
		final int prime = 31;
		int result = super.hashCode();
		result = prime * result + ((keyWord == null) ? 0 : keyWord.hashCode());
		return result;
	}

	@Override
	public boolean equals(Object obj) {
		if (this == obj)
			return true;
		if (!super.equals(obj))
			return false;
		if (getClass() != obj.getClass())
			return false;
		KeyWordConfigPart other = (KeyWordConfigPart) obj;
		if (keyWord == null) {
			if (other.keyWord != null)
				return false;
		} else if (!keyWord.equals(other.keyWord))
			return false;
		return true;
	}

}

RegexConfigPart.java

package com.sopovs.moradanen.gson;

public class RegexConfigPart extends AbstractConfigPart {

  private String regex;

	public RegexConfigPart() {
	}

	public RegexConfigPart(boolean uniqueOnly, int threshold, String regex) {
		super(uniqueOnly, threshold);
		this.regex = regex;
	}

	public String getRegex() {
		return regex;
	}

	public void setRegex(String regex) {
		this.regex = regex;
	}

	@Override
	public int hashCode() {
		final int prime = 31;
		int result = super.hashCode();
		result = prime * result + ((regex == null) ? 0 : regex.hashCode());
		return result;
	}

	@Override
	public boolean equals(Object obj) {
		if (this == obj)
			return true;
		if (!super.equals(obj))
			return false;
		if (getClass() != obj.getClass())
			return false;
		RegexConfigPart other = (RegexConfigPart) obj;
		if (regex == null) {
			if (other.regex != null)
				return false;
		} else if (!regex.equals(other.regex))
			return false;
		return true;
	}

}