Step 1:
Open the project's folder, then go to : .idea/libraries/ you should find here a file by maven dependency.
Delete the jackson-core and jackson-databinding files.
Step 2: Remove maven dependency
Remove the two dependencies from `pom.xml' file. (do not comment out, erase the lines).
Step 3: Check Intellij project config
Open project structure windows (clic on the top parent folder in Intellij then press F4), then go to Libraries tab. ensure the two dependencies are not present, if there are, delete them as well (with the '-' button at top).
Step 4: Remove all cached maven libraries
Go to your home folder, for windows : C:\Users\<YOUR_NAME>\.m2\, here remove the repository folder.
Step 5: Reimport the project
In intellij : Right click the top folder of your project then > Maven > Reimport.
Step 6: Add maven dep
Add your two dependencies to pom.xml.
Step 8: Build your project.
Launch your project.
This should work.
Step 1:
Open the project's folder, then go to : .idea/libraries/ you should find here a file by maven dependency.
Delete the jackson-core and jackson-databinding files.
Step 2: Remove maven dependency
Remove the two dependencies from `pom.xml' file. (do not comment out, erase the lines).
Step 3: Check Intellij project config
Open project structure windows (clic on the top parent folder in Intellij then press F4), then go to Libraries tab. ensure the two dependencies are not present, if there are, delete them as well (with the '-' button at top).
Step 4: Remove all cached maven libraries
Go to your home folder, for windows : C:\Users\<YOUR_NAME>\.m2\, here remove the repository folder.
Step 5: Reimport the project
In intellij : Right click the top folder of your project then > Maven > Reimport.
Step 6: Add maven dep
Add your two dependencies to pom.xml.
Step 8: Build your project.
Launch your project.
This should work.
Run the maven command "mvn dependency:tree" in the directory which contains the parent pomx.mxl file, you can find if you have 2.5.4 there. Maybe you add other jars which also import version 2.5.4, then you should exclude the 2.5.4 version.
Also you can check the local Maven repository, and delete the 2.5.4 version Jackson.
Videos
You can go to Preferences -> Build, Execution, Deployment -> Build Tools -> Maven -> Importing and check the box that says Import Maven projects automatically.
In Mac, you can do Command + Shift + A, then enter the action reimport, then click on Reimport all Maven projects.
As mentioned by @maheeka in the question's comments, if the project is a Maven project, the simplest way to achieve updating changed external libraries is to right-click on the project, and select Maven > Reload project.
You can actually see IntelliJ re-indexing the changed libraries individually during the operation in the bottom right status bar.
Tested on v2021.1 Ultimate.