解决方法 application.yml

server:
  # 单位 KB
  max-http-header-size: 100000

java.lang.IllegalArgumentException: Request header is too large
    at org.apache.coyote.http11.Http11InputBuffer.fill(Http11InputBuffer.java:721) ~[tomcat-embed-core-9.0.21.jar:9.0.21]
    at org.apache.coyote.http11.Http11InputBuffer.parseRequestLine(Http11InputBuffer.java:449) ~[tomcat-embed-core-9.0.21.jar:9.0.21]
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:294) ~[tomcat-embed-core-9.0.21.jar:9.0.21]
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) [tomcat-embed-core-9.0.21.jar:9.0.21]
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:853) [tomcat-embed-core-9.0.21.jar:9.0.21]
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1587) [tomcat-embed-core-9.0.21.jar:9.0.21]
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-9.0.21.jar:9.0.21]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [na:1.8.0_172]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [na:1.8.0_172]
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-9.0.21.jar:9.0.21]
    at java.lang.Thread.run(Thread.java:748) [na:1.8.0_172]

原文：https://www.cnblogs.com/lick468/p/11108988.html