method one:
The source in debug Configurations is Default. Delete Defaul. Add Java Project selects the project, other defaults. After modification, as shown in the figure:
debug can see the source code
Method Two:
You can add workspace in the source, and if it is a multi-project check Resolve workspace atifacts
Method three:
The default file of debug configration --"source --" must (The suspend Thread and suspend jvm in the breakpoint were also adjusted in the middle, and there was no change in the end, which should not be the problem)