使用idea开发工具正常，打包发布到服务器提示thymeleaf找不到模板

template might not exist or might not be accessible by any of the configured Template Resolvers

问题描述：

网站发布到服务器，某个网页提示找不到thymeleaf模板，本地调试时，使用idea开发工具一切正常！服务端应用错误信息如下：

14:57:39.297 [http-nio-80-exec-12] ERROR o.a.c.c.C.[.[.[.[dispatcherServlet] - [log,175] - Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is org.thymeleaf.exceptions.TemplateInputException: Error resolving template [/portal/index], template might not exist or might not be accessible by any of the configured Template Resolvers] with root cause
org.thymeleaf.exceptions.TemplateInputException: Error resolving template [/portal/index], template might not exist or might not be accessible by any of the configured Template Resolvers
        at org.thymeleaf.engine.TemplateManager.resolveTemplate(TemplateManager.java:869)
        at org.thymeleaf.engine.TemplateManager.parseAndProcess(TemplateManager.java:607)
        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:362)
        at org.thymeleaf.spring5.view.ThymeleafView.render(ThymeleafView.java:189)
        at org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1372)
        at org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1118)
        at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1057)
        at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:943)
        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:626)
        at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:733)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
        at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
        at org.apache.shiro.web.servlet.AdviceFilter.executeChain(AdviceFilter.java:108)
        at org.apache.shiro.web.servlet.AdviceFilter.doFilterInternal(AdviceFilter.java:137)
        at org.apache.shiro.web.servlet.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:125)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
        at org.apache.shiro.web.servlet.AdviceFilter.executeChain(AdviceFilter.java:108)

错误原因

返回的viewName以/开头导致的

@Controller
@RequestMapping("/portal")
public class PortalController {
    
    

    @RequestMapping("/index")
    public String index(){
    
    
    	// viewName不能以/开头，例如"/portal/index"
        return "portal/index";
    }
}    

说明：

spring-boot 版本 2.1.17.RELEASE