tomcat max threads

request requires a thread for the duration of that request. If more simultaneous requests are received than can be handled by the currently available request processing threads, additional threads will be created up to the configured maximum (the value of the maxThreads attribute). If still more simultaneous requests are received, they are stacked up inside the server socket created by the Connector, up to the configured maximum (the value of the acceptCount attribute). Any further simultaneous requests will receive "connection refused" errors, until resources are available to process them

example

application.properties or application.yml to config

server.tomcat.max-threads=400