spring boot控制器无法访问到thymeleaf文件及遇到的其他问题

org.thymeleaf.exceptions.TemplateInputException: An error happened during template parsing (…)

This application has no explicit mapping for /error, so you are seeing this as a fallback.

Fri Aug 05 14:52:42 CST 2022
There was an unexpected error (type=Internal Server Error, status=500).
An error happened during template parsing (template: "class path resource [templates/index.html]" - line 142, col 81)
org.thymeleaf.exceptions.TemplateInputException: An error happened during template parsing (template: "class path resource [templates/index.html]" - line 142, col 81)
	at org.thymeleaf.templateparser.markup.AbstractMarkupTemplateParser.parse(AbstractMarkupTemplateParser.java:239)
	at org.thymeleaf.templateparser.markup.AbstractMarkupTemplateParser.parseStandalone(AbstractMarkupTemplateParser.java:100)
	at org.thymeleaf.engine.TemplateManager.parseAndProcess(TemplateManager.java:666)
	at org.thymeleaf.TemplateEngine.process(TemplateEngine.java:1098)
	at org.thymeleaf.TemplateEngine.process(TemplateEngine.java:1072)
	at org.thymeleaf.spring5.view.ThymeleafView.renderFragment(ThymeleafView.java:366)
	at org.thymeleaf.spring5.view.ThymeleafView.render(ThymeleafView.java:190)
	at org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1404)
	at org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1148)
	at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1087)
	at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:963)
	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006)
	at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:898)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:655)
	at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:764)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:227)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
	at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
	at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
	at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:197)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:97)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:135)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:78)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:360)
	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:399)
	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:890)
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1789)
	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
	at org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191)
	at org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659)
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
	at java.lang.Thread.run(Thread.java:748)
Caused by: org.attoparser.ParseException: (Line = 142, Column = 81) Malformed markup: Attribute "rel" appears more than once in element
	at org.attoparser.MarkupEventProcessorHandler.handleAttribute(MarkupEventProcessorHandler.java:549)
	at org.attoparser.ParsingAttributeSequenceUtil.parseAttributeSequence(ParsingAttributeSequenceUtil.java:275)
	at org.attoparser.ParsingElementMarkupUtil.parseOpenElement(ParsingElementMarkupUtil.java:153)
	at org.attoparser.MarkupParser.parseBuffer(MarkupParser.java:710)
	at org.attoparser.MarkupParser.parseDocument(MarkupParser.java:301)
	at org.attoparser.MarkupParser.parse(MarkupParser.java:257)
	at org.thymeleaf.templateparser.markup.AbstractMarkupTemplateParser.parse(AbstractMarkupTemplateParser.java:230)
	... 48 more

出现该错误的原因是模板引擎无法识别thymeleaf，需要在html文件中加上

而我的文件是

因此，thymeleaf 无法识别该文件。只需添加标题即可。

DOCTYPE clause cannot have a non-null PUBLIC ID and a null SYSTEM ID

Thymleaf -请求的实体不受支持，PUBLICID为"null“，改为：

<!DOCTYPE html>

<html xmlns="http://www.w3.org/1999/xhtml" xmlns:th="http://www.thymeleaf.org">

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE html SYSTEM "http://www.thymeleaf.org/dtd/xhtml1-strict-thymeleaf-spring4-4.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xmlns:th="http://www.thymeleaf.org">`

Attribute “rel” appears more than once in element

元素rel在dom中出现次数过多，这是thymeleaf不允许的。

删除多余的rel属性即可。若出现Attribute "xxx" appears more than once in element删除xxx属性即可。