JacksonJsonMapper.java

package com.jackson.utils;

import java.io.IOException;
import java.util.*;

import org.apache.commons.lang3.StringUtils;

import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.JavaType;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.ObjectWriter;
import com.fasterxml.jackson.datatype.guava.GuavaModule;
import com.fasterxml.jackson.datatype.joda.JodaModule;

/**
 * {@link JsonMapper} implemented with Jackson.
 */
public class JacksonJsonMapper implements JsonMapper {
	private static final String ERROR_WRITING_JSON_STRING = "Error writing JSON string";
	private static final String ERROR_READING_JSON_STRING = "Error reading JSON string";

	private final ObjectMapper mapper;

	public JacksonJsonMapper(ObjectMapper mapper) {
		this.mapper = mapper;
        mapper.registerModule(new GuavaModule());
        mapper.registerModule(new JodaModule());
        this.mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
	}

	@Override
	public <T> T fromJson(String json, Class<T> type) {
		if (StringUtils.isEmpty(json)) {
			// TODO fix for Jackson not respecting
			// ACCEPT_EMPTY_STRING_AS_NULL_OBJECT should be investigated further
			return null;
		}

		try {
			return mapper.readValue(json, type);
		} catch (IOException ex) {
			throw new JsonMapperException(ERROR_READING_JSON_STRING, ex);
		}
	}

	@Override
	public <T> List<T> listFromJson(String json, Class<T> elementType) {
		if (StringUtils.isEmpty(json)) {
			// TODO fix for Jackson not respecting
			// ACCEPT_EMPTY_STRING_AS_NULL_OBJECT should be investigated further
			return Collections.emptyList();
		}

		JavaType javaType = mapper.getTypeFactory().constructCollectionType(List.class, elementType);
		try {
			return mapper.readValue(json, javaType);
		} catch (IOException ex) {
			throw new JsonMapperException(ERROR_READING_JSON_STRING, ex);
		}
	}

	@Override
	public <K, V> Map<K, V> mapFromJson(String json, Class<K> keyType, Class<V> valueType) {
		if (StringUtils.isEmpty(json)) {
			// TODO fix for Jackson not respecting
			// ACCEPT_EMPTY_STRING_AS_NULL_OBJECT should be investigated further
			return null;
		}

		JavaType javaType = mapper.getTypeFactory().constructMapType(HashMap.class, keyType, valueType);
		try {
			return mapper.readValue(json, javaType);
		} catch (IOException ex) {
			throw new JsonMapperException(ERROR_READING_JSON_STRING, ex);
		}
	}

	@Override
	public <T> Set<T> setFromJson(String json, Class<T> elementType) {
		if (StringUtils.isEmpty(json)) {
			// TODO fix for Jackson not respecting
			// ACCEPT_EMPTY_STRING_AS_NULL_OBJECT should be investigated further
			return Collections.emptySet();
		}

		JavaType javaType = mapper.getTypeFactory().constructCollectionType(Set.class, elementType);
		try {
			return mapper.readValue(json, javaType);
		} catch (IOException ex) {
			throw new JsonMapperException(ERROR_READING_JSON_STRING, ex);
		}
	}

	@Override
	public String toJson(Object obj, Object... other) {
		try {
			if (other == null || other.length == 0) {
				return mapper.writeValueAsString(obj);
			}
			return mapper.writeValueAsString(asList(obj, other));
		} catch (IOException ex) {
			throw new JsonMapperException(ERROR_WRITING_JSON_STRING, ex);
		}
	}

	@Override
	public String toJson(Class<?> rootType, Object... objs) {
		try {
			ObjectWriter writerWithType = mapper.writerFor(rootType);
			if (objs.length == 1) {
				return writerWithType.writeValueAsString(objs[0]);
			}
			return writerWithType.writeValueAsString(asList(objs));
		} catch (IOException ex) {
			throw new JsonMapperException(ERROR_WRITING_JSON_STRING, ex);
		}
	}

	@SuppressWarnings("rawtypes")
	@Override
	public String toJson(List obj, Class<?> elementType, Object... other) {
		try {
			if (other == null || other.length == 0) {
				JavaType rootType = mapper.getTypeFactory().constructCollectionType(List.class, elementType);
				return mapper.writerFor(rootType).writeValueAsString(obj);
			}
			return mapper.writeValueAsString(asList(obj, other));
		} catch (IOException ex) {
			throw new JsonMapperException(ERROR_WRITING_JSON_STRING, ex);
		}
	}

	private List<Object> asList(Object obj, Object... other) {
		List<Object> merge = new ArrayList<>(other.length + 1);
		merge.add(obj);
		Collections.addAll(merge, other);
		return merge;
	}

}