How did European exploration affect east Asian countries?

For years, the cultures of East Asia had heavily resisted any attempt by foreign powers to open up to maritime trade. In China, and its de facto protectorate of Korea, much of this was due to the idea that China, as the Middle Kingdom, had little to learn from the outside world. After all, on all sides, it was surrounded by barbarians, most epitomized by the Mongols to the north. And it was better for the survival of the kingdom if all external influence was avoided in favor of traditional Confucian teachings. In Japan, the hesitation in regards to outside trade was similar, but instead of being rooted in an admiration for Chinese indigenous culture, it was instead based on the idea that Japan should only adopt those cultural practices that particularly suited its society. It was for this reason that Japan had traditionally sent envoys to China to learn the best of Chinese practices, but to ignore aspects that would not sit well in Japanese culture.

That said, there were exceptions. Zheng He, a Chinese admiral, led a massive fleet in an expedition of trade and goodwill throughout the South China Sea and the Indian Ocean. He established contacts with cultures as far away as Africa. Notably, however, any talk of Zheng He reaching America is simply not true - his men would have introduced the same diseases that devastated native populations' decades later when Columbus arrived. However far reaching Zheng He's expeditions were, his exploits were largely ignored by the next Imperial administration, which chose to focus more on internal affairs than expressing Chinese power abroad.

Trade Goods and Customs

However, despite the best efforts of the powers that be in China, Japan, and Korea, the temptation of goods was simply too great. Principle among these was silk, which was legendary since the Roman period for its quality in the West. However, it wasn't just silk that the Europeans were after. The East Asians still had porcelain, tea, and foods that could not be obtained in such quality anywhere else.

Explanation:

there is an explationation of this on a site called crash   course world history 1