Grails入门：Hello World示例出现500错误

问题描述 #

我刚接触Grails，了解一些Groovy语法，但主要是Java开发者。按照官方指南完成Hello World示例项目创建后，首页http://localhost:8080可以正常访问，但访问http://localhost:8080/hello时出现500错误，日志提示无法找到名为'index'的视图。严格遵循指南步骤操作，怀疑是否指南未适配当前Grails版本导致问题。

问题原因 #

Grails的默认行为是：当控制器方法没有指定返回值或返回null时，会自动尝试在对应目录下寻找匹配的视图文件。比如HelloController的index()方法如果没有返回内容，框架会去grails-app/views/hello/目录查找index.gsp、index.html这类视图文件，找不到就会触发这个错误。

解决办法 #

有两种快速修复方式：

方式一：添加对应视图文件 #

在grails-app/views/目录下新建hello文件夹，然后创建index.gsp文件，写入简单内容即可：

<html>
    <head>
        <title>Hello Page</title>
    </head>
    <body>
        <h1>Hello World!</h1>
    </body>
</html>

方式二：在控制器方法中直接返回响应 #

修改HelloController的index方法，直接输出响应内容，不需要依赖视图文件：

class HelloController {
    def index() {
        render "Hello World!"
    }
}

错误日志详情 #

grails> run-app
| Running application.....
Grails application running at http://localhost:8080 in environment: development
<=======2023-01-30 16:53:11.391 ERROR --- [nio-8080-exec-8] .a.c.c.C.[.[.[.[grailsDispatcherServlet] : Servlet.service() for servlet [grailsDispatcherServlet] in context with path [] threw exception [Could not resolve view with name 'index' in servlet with name 'grailsDispatcherServlet'] with root cause

javax.servlet.ServletException: Could not resolve view with name 'index' in servlet with name 'grailsDispatcherServlet'
        at org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1384)
        at org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1149)
        at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1088)
        at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:964)
        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:670)
        at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:779)
        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.grails.web.servlet.mvc.GrailsWebRequestFilter.doFilterInternal(GrailsWebRequestFilter.java:77)
        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.grails.web.filters.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:67)
        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.springframework.boot.actuate.metrics.web.servlet.WebMvcMetricsFilter.doFilterInternal(WebMvcMetricsFilter.java:96)
        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.CorsFilter.doFilterInternal(CorsFilter.java:91)
        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$ConnectionHandler.process(AbstractProtocol.java:893)
        at org.apache.tomcat.util.net.NioEndpoint$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.base/java.lang.Thread.run(Thread.java:833)

内容的提问来源于stack exchange，提问作者DJViking