google-gson

    /**
     * 
     * 将bean转换成json串，bean中可以包含自定义属性，<br>
     * 转换后的json串是有层次结构的<br>
     * Date类型的将被按字符串赋给json串<br>
     * <link>http://sites.google.com/site/gson/Home</link>
     * 
     * @param bean
     * @return json串
     */
    public static String bean2json(Object bean) {
        Gson gson = new GsonBuilder().registerTypeAdapter(java.sql.Date.class,
                new SQLDateSerializer()).setDateFormat(DateFormat.LONG)
                .create();
        return gson.toJson(bean);
    }

SQLDateSerializer.class

public class SQLDateSerializer implements JsonSerializer<java.sql.Date> {

    public JsonElement serialize(java.sql.Date src, Type typeOfSrc,
            JsonSerializationContext context) {
        return new JsonPrimitive(src.toString());
    }
}