GsonUtils.java

package br.com.citframework.util;

import java.io.Reader;
import java.lang.reflect.Type;

import com.google.gson.ExclusionStrategy;
import com.google.gson.FieldAttributes;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.annotations.Expose;

public final class GsonUtils {

    private static final Gson GSON = createGson(true, null);

    private static final Gson GSON_NO_NULLS = createGson(false,null);
    
    private static final String DATE_FORMAT = "MMM dd, yyyy";

    /**
     * Create the standard {@link Gson} configuration
     *
     * @return created gson, never null
     */
    public static final Gson createGson() {
        return createGson(true,null);
    }

    /**
     * Create the standard {@link Gson} configuration
     *
     * @param serializeNulls whether nulls should be serialized
     * @return created gson, never null
     */
    public static final Gson createGson(final boolean serializeNulls, String dateFormat) {
        final GsonBuilder builder = new GsonBuilder();
        if (serializeNulls) {
            builder.serializeNulls();
        }      
        builder.setDateFormat( dateFormat != null ? dateFormat : DATE_FORMAT);
        builder.setExclusionStrategies(new ExclusionStrategy() {
        	
    		public boolean shouldSkipClass(Class<?> arg0) {
                return false;
            }

            public boolean shouldSkipField(FieldAttributes f) {
            	 final Expose expose = f.getAnnotation(Expose.class);
                 return expose != null;
            }

        });
        return builder.create();
    }

    /**
     * Get reusable pre-configured {@link Gson} instance
     *
     * @return Gson instance
     */
    public static final Gson getGson() {
        return GSON;
    }

    /**
     * Get reusable pre-configured {@link Gson} instance
     *
     * @return Gson instance
     */
    public static final Gson getGson(final boolean serializeNulls) {
        return serializeNulls ? GSON : GSON_NO_NULLS;
    }

    /**
     * Convert object to json
     *
     * @return json string
     */
    public static final String toJson(final Object object) {
        return toJson(object, true);
    }

    /**
     * Convert object to json
     *
     * @return json string
     */
    public static final String toJson(final Object object, final boolean includeNulls) {
        return includeNulls ? GSON.toJson(object) : GSON_NO_NULLS.toJson(object);
    }

    /**
     * Convert string to given type
     *
     * @return instance of type
     */
    public static final <V> V fromJson(String json, Class<V> type) {
        return GSON.fromJson(json, type);
    }

    /**
     * Convert string to given type
     *
     * @return instance of type
     */
    public static final <V> V fromJson(String json, Type type) {
        return GSON.fromJson(json, type);
    }

    /**
     * Convert content of reader to given type
     *
     * @return instance of type
     */
    public static final <V> V fromJson(Reader reader, Class<V> type) {
        return GSON.fromJson(reader, type);
    }

    /**
     * Convert content of reader to given type
     *
     * @return instance of type
     */
    public static final <V> V fromJson(Reader reader, Type type) {
        return GSON.fromJson(reader, type);
    }
    
}