build task error

[xfmyh]

java modules project => openjdk 15 + spring boot 2.4 + gradle 2.22.3

reference ==> https://docs.gradle.org/current/samples/sample_java_modules_multi_project.html

build task error

build.gradle
buildscript {
repositories {
maven{ url 'http://maven.aliyun.com/nexus/content/groups/public/'}
}
}

plugins {
id 'org.springframework.boot' version '2.4.0'
id 'io.spring.dependency-management' version '1.0.10.RELEASE'
id "org.beryx.jlink" version "2.22.3"
id 'java'
id 'application'
}

repositories {
maven { url 'http://maven.aliyun.com/nexus/content/groups/public/' }

jcenter()

}

java {
sourceCompatibility = JavaVersion.VERSION_15
targetCompatibility = JavaVersion.VERSION_15
modularity.inferModulePath = true

}

version = '0.0.1-SNAPSHOT'
group = 'com.demo'

tasks.compileJava {
// use the project's version or define one directly
options.javaModuleVersion = provider { project.version }
}

dependencies {
testImplementation 'junit:junit:4.13'

implementation 'com.google.guava:guava:29.0-jre'

implementation group: 'org.springframework.boot', name: 'spring-boot-starter'
//implementation group: 'org.springframework.boot', name: 'spring-boot-starter-security'
implementation (group: 'org.springframework.boot', name: 'spring-boot-starter-web'){
    exclude(module: 'spring-boot-starter-tomcat')
}
implementation group: 'org.springframework.boot', name: 'spring-boot-starter-undertow', version: '2.4.0'

}

application {
mainClass = 'com.demo/com.demo.App'
}

src/main/java/module-info.java
module com.demo {
requires spring.boot;
requires spring.boot.autoconfigure;
opens com.demo to spring.core;
exports com.demo;
}
src/main/java/com/demo/App.class

package com.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class App {
public static void main(String[] args) {
SpringApplication.run(App.class,args);
}
}

build task

Configure project :app
Using insecure protocols with repositories has been deprecated. This is scheduled to be removed in Gradle 7.0. Switch Maven repository 'maven(http://maven.aliyun.com/nexus/content/groups/public/)' to a secure protocol (like HTTPS) or allow insecure protocols. See https://docs.gradle.org/6.7.1/dsl/org.gradle.api.artifacts.repositories.UrlArtifactRepository.html#org.gradle.api.artifacts.repositories.UrlArtifactRepository:allowInsecureProtocol for more details.

Task :app:compileJava UP-TO-DATE
Task :app:processResources UP-TO-DATE
Task :app:classes UP-TO-DATE
Task :app:bootJarMainClassName UP-TO-DATE
Task :app:bootJar FAILED
4 actionable tasks: 1 executed, 3 up-to-date

FAILURE: Build failed with an exception.

• What went wrong:
  Execution failed for task ':app:bootJar'.

Failed to calculate the value of task ':app:bootJar' property 'mainClass'.
Main class name has not been configured and it could not be resolved

• Try:
  Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.

• Get more help at https://help.gradle.org

BUILD FAILED in 1s