Unable to redirect to the correct html in Spring Controller @GetMapping -- module-info.java is causing Error resolving template

Question

problem-situation

1.

I have a extremely simple Controller

package com.redfrog.note;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;

@Controller
public class BallController {

  @GetMapping("/p1")
  public String p1() { return "main"; }

}

And this is the Folder structure

+---src
|   +---main
|   |   +---java
|   |   |   |
|   |   |   \---com
|   |   |       \---redfrog
|   |   |           \---note
|   |   |                   BallController.java
|   |   |                   TestSpringHibernate1Application.java
|   |   |
|   |   \---resources
|   |       |   application.properties
|   |       |
|   |       +---static
|   |       |       index.html
|   |       |
|   |       \---templates
|   |               main.html

When I call http://127.0.0.1:8080/p1 it displays the content of main.html
-> good.

2.

Now I add in a module-info.java, & just do the exact same thing
-> error below is thrown::

(in Chrome)

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

Sun Apr 30 23:10:07 CST 2023
There was an unexpected error (type=Internal Server Error, status=500).
Error resolving template [main], template might not exist or might not be accessible by any of the configured Template Resolvers
org.thymeleaf.exceptions.TemplateInputException: Error resolving template [main], template might not exist or might not be accessible by any of the configured Template Resolvers
    at [email protected]/org.thymeleaf.engine.TemplateManager.resolveTemplate(TemplateManager.java:869)
    at [email protected]/org.thymeleaf.engine.TemplateManager.parseAndProcess(TemplateManager.java:607)
    at [email protected]/org.thymeleaf.TemplateEngine.process(TemplateEngine.java:1098)
    at [email protected]/org.thymeleaf.TemplateEngine.process(TemplateEngine.java:1072)
    at [email protected]/org.thymeleaf.spring5.view.ThymeleafView.renderFragment(ThymeleafView.java:366)
    at [email protected]/org.thymeleaf.spring5.view.ThymeleafView.render(ThymeleafView.java:190)
    at [email protected]/org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1406)
    at [email protected]/org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1150)
    at [email protected]/org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1089)
    at [email protected]/org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:965)
    at [email protected]/org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006)
    at [email protected]/org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:898)
    at [email protected]/javax.servlet.http.HttpServlet.service(HttpServlet.java:529)
    at [email protected]/org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883)
    at [email protected]/javax.servlet.http.HttpServlet.service(HttpServlet.java:623)
    at [email protected]/org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:209)
    at [email protected]/org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:153)
    at [email protected]/org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51)
    at [email protected]/org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:178)
    at [email protected]/org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:153)
    at [email protected]/org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100)
    at [email protected]/org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117)
    at [email protected]/org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:178)
    at [email protected]/org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:153)
    at [email protected]/org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93)
    at [email protected]/org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117)
    at [email protected]/org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:178)
    at [email protected]/org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:153)
    at [email protected]/org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201)
    at [email protected]/org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117)
    at [email protected]/org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:178)
    at [email protected]/org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:153)
    at [email protected]/org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:167)
    at [email protected]/org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:90)
    at [email protected]/org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:481)
    at [email protected]/org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:130)
    at [email protected]/org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:93)
    at [email protected]/org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74)
    at [email protected]/org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
    at [email protected]/org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:389)
    at [email protected]/org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:63)
    at [email protected]/org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:926)
    at [email protected]/org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1791)
    at [email protected]/org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:52)
    at [email protected]/org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191)
    at [email protected]/org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659)
    at [email protected]/org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.base/java.lang.Thread.run(Thread.java:833)

(in Postman, omitted some)

{
    "timestamp": "2023-04-30T15:01:24.640+00:00",
    "status": 500,
    "error": "Internal Server Error",
    "trace": "org.thymeleaf.exceptions.TemplateInputException: Error resolving template [main], template might not exist or might not be accessible by any of the configured Template Resolvers\r\n\tat [email protected]/org.thymeleaf.engine.TemplateManager.resolveTemplate(TemplateManager.java:869)\r\n\tat

problem-question

How do I fix this?

I need to use module-info.java.

---

misc

I tried to look at the source code in debug mode.

Seems the code goes to return null; // << goes to here .

But I have no knowledge to dig deeper.

public abstract class AbstractTemplateResolver implements ITemplateResolver {

    public final TemplateResolution resolveTemplate(
            final IEngineConfiguration configuration,
            final String ownerTemplate, final String template,
            final Map<String, Object> templateResolutionAttributes) {

        Validate.notNull(configuration, "Engine Configuration cannot be null");
        // ownerTemplate CAN be null
        Validate.notNull(template, "Template Name cannot be null");
        // templateResolutionAttributes CAN be null

        if (!computeResolvable(configuration, ownerTemplate, template, templateResolutionAttributes)) {
            return null;
        }

        final ITemplateResource templateResource = computeTemplateResource(configuration, ownerTemplate, template, templateResolutionAttributes);
        if (templateResource == null) {
            return null;
        }

        if (this.checkExistence && !templateResource.exists()) { // will only check if flag set to true
            return null; // << goes to here 
        }

        return new TemplateResolution(
                templateResource,
                this.checkExistence,
                computeTemplateMode(configuration, ownerTemplate, template, templateResolutionAttributes),
                this.useDecoupledLogic,
                computeValidity(configuration, ownerTemplate, template, templateResolutionAttributes));
        
    }

---

more files

module-info.java

module sswwy {
  exports com.redfrog.note;

  opens com.redfrog.note;

  requires java.base;
  requires java.compiler;
  requires java.datatransfer;
  requires java.desktop;
  requires java.instrument;
  requires java.logging;
  requires java.management;
  requires java.management.rmi;
  requires java.naming;
  requires java.net.http;
  requires java.prefs;
  requires java.rmi;
  requires java.scripting;
  requires java.se;
  requires java.security.jgss;
  requires java.security.sasl;
  requires java.smartcardio;
  requires java.sql;
  requires java.sql.rowset;
  requires java.transaction.xa;
  requires java.xml;
  requires java.xml.crypto;
  requires jdk.accessibility;
  requires jdk.attach;
  requires jdk.charsets;
  requires jdk.compiler;
  requires jdk.crypto.cryptoki;
  requires jdk.crypto.ec;
  requires jdk.crypto.mscapi;
  requires jdk.dynalink;
  requires jdk.editpad;
  requires jdk.hotspot.agent;
  requires jdk.httpserver;
  requires jdk.internal.ed;
  requires jdk.internal.jvmstat;
  requires jdk.internal.le;
  requires jdk.internal.opt;
  requires jdk.internal.vm.ci;
  requires jdk.internal.vm.compiler;
  requires jdk.internal.vm.compiler.management;
  requires jdk.jartool;
  requires jdk.javadoc;
  requires jdk.jcmd;
  requires jdk.jconsole;
  requires jdk.jdeps;
  requires jdk.jdi;
  requires jdk.jdwp.agent;
  requires jdk.jfr;
  requires jdk.jlink;
  requires jdk.jpackage;
  requires jdk.jshell;
  requires jdk.jsobject;
  requires jdk.jstatd;
  requires jdk.localedata;
  requires jdk.management;
  requires jdk.management.agent;
  requires jdk.management.jfr;
  requires jdk.naming.dns;
  requires jdk.naming.rmi;
  requires jdk.net;
  requires jdk.nio.mapmode;
  requires jdk.random;
  requires jdk.sctp;
  requires jdk.security.auth;
  requires jdk.security.jgss;
  requires jdk.unsupported;
  requires jdk.unsupported.desktop;
  requires jdk.xml.dom;
  requires jdk.zipfs;

  //  requires HikariCP;
  //  requires accessors.smart;
  //  requires android.json;
  //  requires antlr;
  //  requires assertj.core;
  requires attoparser;
  //  requires com.fasterxml.classmate;
  requires com.fasterxml.jackson.annotation;
  //  requires com.sun.istack.runtime;
  //  requires com.sun.xml.txw2;
  //  requires dom4j;
  //  requires jackson.core;
  //  requires jackson.databind;
  //  requires jackson.datatype.jdk8;
  //  requires jackson.datatype.jsr310;
  //  requires jackson.module.parameter.names;
  //  requires jakarta.activation;
  requires java.annotation;
  //  requires java.persistence;
  //  requires java.transaction;
  //  requires java.xml.bind;
  //  requires json.path;
  //  requires json.smart;
  //  requires jsonassert;
  requires jul.to.slf4j;
  //  requires log4j.api;
  requires logback.classic;
  requires logback.core;
  //  requires lombok;
  //  requires mysql.connector.j;
  requires org.apache.logging.slf4j;
  requires org.apache.tomcat.embed.core;
  requires org.apache.tomcat.embed.el;
  requires org.apache.tomcat.embed.websocket;
  //  requires org.apiguardian.api;
  //  requires org.aspectj.weaver;
  //  requires org.glassfish.jaxb.runtime;
  //  requires org.hamcrest;
  //  requires org.hibernate.commons.annotations;
  //  requires org.hibernate.orm.core;
  //  requires org.hibernate.orm.envers;
  //  requires org.jboss.jandex;
  //  requires org.jboss.logging;
  //  requires org.joda.time;
  //  requires org.junit.jupiter;
  //  requires org.junit.jupiter.api;
  //  requires org.junit.jupiter.engine;
  //  requires org.junit.jupiter.params;
  //  requires org.junit.platform.commons;
  //  requires org.junit.platform.engine;
  //  requires org.mockito;
  //  requires org.mockito.junit.jupiter;
  //  requires org.objectweb.asm;
  //  requires org.objenesis;
  //  requires org.opentest4j;
  requires org.slf4j;
  //  requires org.xmlunit;
  requires org.yaml.snakeyaml;
  requires spring.aop;
  //  requires spring.aspects;
  requires spring.beans;
  requires spring.boot;
  requires spring.boot.autoconfigure;
  //  requires spring.boot.devtools;
  requires spring.boot.starter;
  //  requires spring.boot.starter.aop;
  //  requires spring.boot.starter.data.jpa;
  //  requires spring.boot.starter.jdbc;
  requires spring.boot.starter.json;
  requires spring.boot.starter.logging;
  //  requires spring.boot.starter.test;
  requires spring.boot.starter.thymeleaf;
  requires spring.boot.starter.tomcat;
  requires spring.boot.starter.web;
  //  requires spring.boot.test;
  //  requires spring.boot.test.autoconfigure;
  requires spring.context;
  requires spring.core;
  //  requires spring.data.commons;
  //  requires spring.data.envers;
  //  requires spring.data.jpa;
  requires spring.expression;
  requires spring.jcl;
  //  requires spring.jdbc;
  //  requires spring.orm;
  //  requires spring.test;
  //  requires spring.tx;
  requires spring.web;
  requires spring.webmvc;
  //  requires testSpringHibernate;
  requires thymeleaf;
  requires thymeleaf.extras.java8time;
  requires thymeleaf.spring5;
  requires unbescape;
}

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.7.11</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.redfrog</groupId>
    <artifactId>Test_SpringHibernate-1</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>Test_SpringHibernate-1</name>
    <description>Demo project for Spring Boot</description>
    <properties>
        <java.version>17</java.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <scope>runtime</scope>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-thymeleaf</artifactId>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

a complete folder structure (after added module-info.java)

|   .classpath
|   .gitignore
|   .project
|   HELP.md
|   mvnw
|   mvnw.cmd
|   pom.xml
|
+---.mvn
|   \---wrapper
|           maven-wrapper.jar
|           maven-wrapper.properties
|
+---.settings
|       org.eclipse.core.resources.prefs
|       org.eclipse.jdt.apt.core.prefs
|       org.eclipse.jdt.core.prefs
|       org.eclipse.m2e.core.prefs
|       org.springframework.ide.eclipse.prefs
|
+---src
|   +---main
|   |   +---java
|   |   |   |   module-info.java
|   |   |   |
|   |   |   \---com
|   |   |       \---redfrog
|   |   |           \---note
|   |   |                   BallController.java
|   |   |                   TestSpringHibernate1Application.java
|   |   |
|   |   \---resources
|   |       |   application.properties
|   |       |
|   |       +---static
|   |       |       index.html
|   |       |
|   |       \---templates
|   |               main.html
|   |
|   \---test
|       \---java
|           \---com
|               \---redfrog
|                   \---note
\---target
    +---classes
    |   |   application.properties
    |   |   module-info.class
    |   |
    |   +---com
    |   |   \---redfrog
    |   |       \---note
    |   |               BallController.class
    |   |               TestSpringHibernate1Application.class
    |   |
    |   +---META-INF
    |   |   |   MANIFEST.MF
    |   |   |
    |   |   \---maven
    |   |       \---com.redfrog
    |   |           \---Test_SpringHibernate-1
    |   |                   pom.properties
    |   |                   pom.xml
    |   |
    |   +---static
    |   |       index.html
    |   |
    |   \---templates
    |           main.html
    |
    \---test-classes
        \---com
            \---redfrog
                \---note

• (To avoid Exception throw due to any potential missing thing, I just requires nearly everything in module-info.java.)