1. Origin of the problem
When I learned c3p0 for the first time today, the learning materials used were version 0.9.1.2 .
I am lazy and using version 0.9.2 . But when running, an error will be reported:
I searched this error online, and many people said to install the mchange-commons-0.2.jar package.
However, I saw that the learning materials did not install this package separately, and no error was reported. I think it's a jar package version issue
2. Find out
① You can search for 2 c3p0s from mvnrepository:
② The first c3p0 is from version 0.9.2
https://mvnrepository.com/artifact/com.mchange/c3p0
③ The second c3p0 is as of 0.9.1.2
https://mvnrepository.com/artifact/c3p0/c3p0/0.9.1.2
④ Both c3p0 are official, but the storage addresses are different.
And from version 0.9.2 onwards, it needs to be used with the mchange-commons-0.2.jar package:
In order to be consistent with the learning materials, I changed to version 0.9.1.2 , so it does not need to reference other jar packages.
3. Say goodbye correctly
Deleting version 0.9.2 may prompt that the deletion failed, even if the reference code is blocked
. In this case, restart the idea and it will be fine. After restarting, you will find that the version that needs to be deleted is gone:
