问题
I'm just wondering: in my Java application, each time I need to connect to an FTP server, should I create a new FTPClient object, or should I create one FTPClient() object and re-use that each time I connect to an FTP server?
回答1:
Reusing would be better since you wont need a new instance every time you are creating a new connection, even to a new server. Because the connect and disconnect methods can do the job for you.
So reuse as many objects as you can.
回答2:
Both will work, but apache commons.net libraries are not thread safe, so if you do use one client with multiple threads, be aware that you'll have to synchronize access to it.
回答3:
Without knowing exactly what your code has to do (how often it connects, how many files it needs to transfer etc) it's difficult to say.
My personal opinion would be one FTPClient() but connect/authenticate/transfer/disconnect each time you need to do something (assuming there will be a reasonable gap in between). The reasoning is that FTP sessions often have fairly short inactivity time-outs.
来源：https://stackoverflow.com/questions/6892066/apache-commons-net-should-i-create-a-new-ftpclient-object-on-each-connection-or