Erro: Uma conexão estabelecida foi anulada pelo software no computador host

    java.io.IOException: Uma conexão estabelecida foi anulada pelo software no computador host
    	at java.base/sun.nio.ch.SocketDispatcher.write0(Native Method) ~[na:na]
    	at java.base/sun.nio.ch.SocketDispatcher.write(SocketDispatcher.java:54) ~[na:na]
    	at java.base/sun.nio.ch.IOUtil.writeFromNativeBuffer(IOUtil.java:113) ~[na:na]
    	at java.base/sun.nio.ch.IOUtil.write(IOUtil.java:79) ~[na:na]
    	at java.base/sun.nio.ch.IOUtil.write(IOUtil.java:50) ~[na:na]
    	at java.base/sun.nio.ch.SocketChannelImpl.write(SocketChannelImpl.java:484) ~[na:na]
    	at org.apache.tomcat.util.net.NioChannel.write(NioChannel.java:138) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    	at org.apache.tomcat.util.net.NioBlockingSelector.write(NioBlockingSelector.java:101) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    	at org.apache.tomcat.util.net.NioSelectorPool.write(NioSelectorPool.java:152) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    	at org.apache.tomcat.util.net.NioEndpoint$NioSocketWrapper.doWrite(NioEndpoint.java:1253) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    	at org.apache.tomcat.util.net.SocketWrapperBase.doWrite(SocketWrapperBase.java:764) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    	at org.apache.tomcat.util.net.SocketWrapperBase.writeBlocking(SocketWrapperBase.java:584) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    	at org.apache.tomcat.util.net.SocketWrapperBase.write(SocketWrapperBase.java:528) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    	at org.apache.coyote.http11.Http11OutputBuffer$SocketOutputBuffer.doWrite(Http11OutputBuffer.java:546) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    	at org.apache.coyote.http11.filters.ChunkedOutputFilter.doWrite(ChunkedOutputFilter.java:112) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    	at org.apache.coyote.http11.Http11OutputBuffer.doWrite(Http11OutputBuffer.java:193) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    	at org.apache.coyote.Response.doWrite(Response.java:601) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    	at org.apache.catalina.connector.OutputBuffer.realWriteBytes(OutputBuffer.java:339) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    	at org.apache.catalina.connector.OutputBuffer.appendByteArray(OutputBuffer.java:746) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    	at org.apache.catalina.connector.OutputBuffer.append(OutputBuffer.java:675) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    	at org.apache.catalina.connector.OutputBuffer.writeBytes(OutputBuffer.java:386) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    	at org.apache.catalina.connector.OutputBuffer.write(OutputBuffer.java:364) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    	at org.apache.catalina.connector.CoyoteOutputStream.write(CoyoteOutputStream.java:96) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    	at java.base/sun.nio.cs.StreamEncoder.writeBytes(StreamEncoder.java:242) ~[na:na]
    	at java.base/sun.nio.cs.StreamEncoder.implWrite(StreamEncoder.java:312) ~[na:na]
    	at java.base/sun.nio.cs.StreamEncoder.implWrite(StreamEncoder.java:290) ~[na:na]
    	at java.base/sun.nio.cs.StreamEncoder.write(StreamEncoder.java:131) ~[na:na]
    	at java.base/java.io.OutputStreamWriter.write(OutputStreamWriter.java:211) ~[na:na]
    	at java.base/java.io.BufferedWriter.flushBuffer(BufferedWriter.java:120) ~[na:na]
    	at java.base/java.io.BufferedWriter.write(BufferedWriter.java:233) ~[na:na]
    	at java.base/java.io.Writer.write(Writer.java:249) ~[na:na]
    	at java.base/java.io.Writer.append(Writer.java:322) ~[na:na]
    	at com.vaadin.flow.server.BootstrapHandler.writeBootstrapPage(BootstrapHandler.java:493) ~[flow-server-2.4.6.jar:2.4.6]
    	at com.vaadin.flow.server.BootstrapHandler.synchronizedHandleRequest(BootstrapHandler.java:482) ~[flow-server-2.4.6.jar:2.4.6]
    	at com.vaadin.flow.server.SynchronizedRequestHandler.handleRequest(SynchronizedRequestHandler.java:40) ~[flow-server-2.4.6.jar:2.4.6]
    	at com.vaadin.flow.server.VaadinService.handleRequest(VaadinService.java:1547) ~[flow-server-2.4.6.jar:2.4.6]
    	at com.vaadin.flow.server.VaadinServlet.service(VaadinServlet.java:247) ~[flow-server-2.4.6.jar:2.4.6]
    	at com.vaadin.flow.spring.SpringServlet.service(SpringServlet.java:111) ~[vaadin-spring-12.3.2.jar:na]
    	at javax.servlet.http.HttpServlet.service(HttpServlet.java:733) ~[tomcat-embed-core-9.0.41.jar:4.0.FR]
    	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    	at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:712) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    	at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:459) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    	at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:352) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    	at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:312) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    	at org.springframework.web.servlet.mvc.ServletForwardingController.handleRequestInternal(ServletForwardingController.java:141) ~[spring-webmvc-5.3.3.jar:5.3.3]
    	at org.springframework.web.servlet.mvc.AbstractController.handleRequest(AbstractController.java:177) ~[spring-webmvc-5.3.3.jar:5.3.3]
    	at org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter.handle(SimpleControllerHandlerAdapter.java:52) ~[spring-webmvc-5.3.3.jar:5.3.3]
    	at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1060) ~[spring-webmvc-5.3.3.jar:5.3.3]
    	at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:962) ~[spring-webmvc-5.3.3.jar:5.3.3]
    	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006) ~[spring-webmvc-5.3.3.jar:5.3.3]
    	at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:898) ~[spring-webmvc-5.3.3.jar:5.3.3]
    	at javax.servlet.http.HttpServlet.service(HttpServlet.java:626) ~[tomcat-embed-core-9.0.41.jar:4.0.FR]
    	at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883) ~[spring-webmvc-5.3.3.jar:5.3.3]
    	at javax.servlet.http.HttpServlet.service(HttpServlet.java:733) ~[tomcat-embed-core-9.0.41.jar:4.0.FR]
    	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) ~[tomcat-embed-websocket-9.0.41.jar:9.0.41]
    	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    	at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) ~[spring-web-5.3.3.jar:5.3.3]
    	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.3.3.jar:5.3.3]
    	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    	at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) ~[spring-web-5.3.3.jar:5.3.3]
    	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.3.3.jar:5.3.3]
    	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    	at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) ~[spring-web-5.3.3.jar:5.3.3]
    	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.3.3.jar:5.3.3]
    	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:97) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:542) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:143) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:78) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:374) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:888) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1597) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) ~[na:na]
    	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) ~[na:na]
    	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    	at java.base/java.lang.Thread.run(Thread.java:830) ~[na:na]

O QUE É? COMO RESOLVER? ESTOU USANDO VAADIN 14.4 + SPRING + MYSQL

Estou com o mesmo problema

@Marcel_Motta

Marcel, qual IDE vc utiliza?

já arrumei, faltou () em …hide(); no primefaces

Uso Eclipse