Building a Custom Jackson Deserializer

YesNoBooleanDeserializer.java

package com.robinhowlett.blog;

import java.io.IOException;

import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.core.JsonToken;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.JsonDeserializer;

/**
 * Deserializer that case-insensitively deserializes 
 * "yes", "no", and null JSON field values to 
 * true, false, and false respectively
 * 
 * @author robin
 *
 */
public class YesNoBooleanDeserializer extends JsonDeserializer<Boolean> {

	protected static final String NO = "no";
	protected static final String YES = "yes";

	/* (non-Javadoc)
	 * @see com.fasterxml.jackson.databind.JsonDeserializer#deserialize(com.fasterxml.jackson.core.JsonParser, com.fasterxml.jackson.databind.DeserializationContext)
	 */
	@Override
	public Boolean deserialize(JsonParser jp, DeserializationContext ctxt)
			throws IOException, JsonProcessingException {
		JsonToken currentToken = jp.getCurrentToken();
		
		if (currentToken.equals(JsonToken.VALUE_STRING)) {
			String text = jp.getText().trim();
			
			if (YES.equalsIgnoreCase(text)) {
				return Boolean.TRUE;
			} else if (NO.equalsIgnoreCase(text)) {
				return Boolean.FALSE;
			}
			
			throw ctxt.weirdStringException(text, Boolean.class, 
					"Only \"" + YES + "\" or \"" + NO + "\" values supported");
		} else if (currentToken.equals(JsonToken.VALUE_NULL)) {
			return getNullValue();
		}
		
		throw ctxt.mappingException(Boolean.class);
	}
	
	@Override
	public Boolean getNullValue() {
		return Boolean.FALSE;
	}

}

YesNoBooleanDeserializerTest.java

package com.robinhowlett.blog;

import static org.junit.Assert.assertFalse;
import static org.junit.Assert.assertTrue;

import java.io.IOException;

import org.junit.After;
import org.junit.Before;
import org.junit.Test;

import com.fasterxml.jackson.core.JsonParseException;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.annotation.JsonDeserialize;

/**
 * Test that "yes", "no" and null values that are deserialized
 * with {@link YesNoBooleanDeserializer} return true, false, and
 * false respectively
 * 
 * @author robin
 *
 */
public class YesNoBooleanDeserializerTest {
	
	private ObjectMapper mapper;

	/**
	 * @throws java.lang.Exception
	 */
	@Before
	public void setUp() throws Exception {
		mapper = new ObjectMapper();
	}

	/**
	 * @throws java.lang.Exception
	 */
	@After
	public void tearDown() throws Exception {
		mapper = null;
	}

	@Test
	public void yes() throws JsonParseException, IOException {
		String yes = "\"" + YesNoBooleanDeserializer.YES + "\"";
		Boolean result = deserialize(yes);
		assertTrue(result);
		
		result = deserialize(yes.toUpperCase());
		assertTrue(result);
	}
	
	@Test
	public void no() throws JsonParseException, IOException {
		String no = "\"" + YesNoBooleanDeserializer.NO + "\"";
		Boolean result = deserialize(no);
		assertFalse(result);
		
		result = deserialize(no.toUpperCase());
		assertFalse(result);
	}
	
	@Test
	public void nullValue() throws JsonParseException, IOException {
		// null values must deserialize as Boolean.FALSE to support primitives
		Boolean result = deserialize(null);		
		assertFalse(result);
	}
	
	@Test(expected=JsonMappingException.class)
	public void neitherYesOrNo() throws JsonParseException, IOException {
		deserialize("\"never\"");
	}

	private Boolean deserialize(String yesOrNo) throws IOException, JsonParseException,
			JsonProcessingException {
		TestObject testObject = mapper.readValue("{\"exists\":" + yesOrNo + "}", TestObject.class);
		
		return testObject.getExists();
	}
	
	private static class TestObject {
		
		@JsonDeserialize(using = YesNoBooleanDeserializer.class)
		private final Boolean exists = null;
		
		public Boolean getExists() {
			return exists;
		}
	}

}

Thank you, it works