EU sanctions on shipment of Iranian oil have not prevented China and Japan from receiving shipments. Japan says it will provide coverage for Iranian tankers as they cannot get commercial insurance. China has offered Iran its own tankers to move crude oil.
Japan has approved government insurance of up to 7.6 billion for each tanker. Next month China and Japan combined will load about 620,000 barrels a day next month..
The EU ban includes not just a ban on member countries importing Iranian oil but also EU insurance firms from covering Iran's exports. The ban comes in force July 1st.
The measure will effect not just China and Japan but also South Korea and India. Both the EU and U.S. have imposed sanctions which are supposed to force Iran to give up its nuclear program.
India won an exemption from U.S. sanctions this week. India also may give insurance guarantees to avoid the EU ban on insurance. On the other hand South Korea has failed to get an exemption from U.S. sanctions. South Korea intends to simply not import crude from Iran. For more see this article.