Joy comes from being in God's presence. It's in the Bible, Psalm 16:8-9, TLB. "I am always thinking of the Lord; and because He is so near, I never need to stumble or to fall. Heart, body, and soul are filled with joy."
Joy comes from keeping God's commandments. It's in the Bible, John 15:10-11, NKJV. "If you keep My commandments, you will abide in My love, just as I have kept My Father's commandments and abide in His love. These things I have spoken to you, that My joy may remain in you, and that your joy may be full."
Joy is a gift of the Holy Spirit. It's in the Bible, Galatians 5:22-23, TLB. "But when the Holy Spirit controls our lives He will produce this kind of fruit in us: love, joy, peace, patience, kindness, goodness, faithfulness, gentleness and self-control."
We can be joyful in spite of our circumstances. It's in the Bible, Philippians 4:4, TLB. "Always be full of joy in the Lord; I say it again, rejoice!"