How to fix Caused by: java.sql.SQLException: ORA-01109: database not open

sudo su - oracle

sqlplus / as sysdba

SYS@sukhoi> show pdbs;

When DB is unable to connect () login to the Db and check the same:
ALTER PLUGGABLE DATABASE <PDB_SEED_32K open read only;

SYS@sukhoi> show pdbs;