All over the world people are in search of happiness. The word "happy" comes from the same origin as "perhaps", "haphazard" and "happenings". The root is "hap" - a chance occurrence. This is why our happiness can come and go dependant upon what is going on around us - the weather, our weight, even the traffic can trigger a change in our state of happiness.
Joy, on the other hand, is one aspect of the fruit of the Holy Spirit. It is not dependant upon what is happening but upon us being re-filled and refreshed with God again and again. It is wholly based on our ongoing relationship with God. In Thessalonians we are told to "Rejoice always" (1 Thes 5 v 16); this is possible when we regularly look into His Word and meditate on the attributes of God. Also, as we pray and worship our faith gets built up and this encourages joy in our life.
When we are joy-filled, we don't rely on happiness to put warmth in our heart and a smile on our face - our Lord has already done it for us.
Lord I thank You for the gifts of Jesus and Your Holy Spirit. Thank You that I am not reliant upon happenings, but upon the steadfastness of Your character, for joy to be evident in my life today.