I found a circle on the Internet, but there was no solution by jetty8. Through analysis, we know the _maxFormContentSize control parameter size of the org.eclipse.jetty.server.handler.ContextHandler class.
By rewriting this class in the project src, modify the _maxFormContentSize property. The classes in the jar package will be overwritten during runtime, which is a bit stupid but solves the problem.
private int _maxFormContentSize = Integer.getInteger(“org.eclipse.jetty.server.Request.maxFormContentSize”,600000).intValue();