Springboot CLI - Hot Reload Not Triggering

[TheGitHubGuy1]

Referenced Docs:
https://docs.spring.io/spring-boot/docs/2.1.7.RELEASE/gradle-plugin/reference/html/
https://docs.spring.io/spring-boot/docs/2.1.7.RELEASE/reference/html/using-boot-devtools.html
https://guides.gradle.org/building-spring-boot-2-projects-with-gradle/

SpringBoot Version: v2.1.7.RELEASE
Gradle Version: 5.5.1
OS: Ubuntu 18.04.3 LTS
Java Version: 11.0.4

I built the project with command: gradle init --type java-application
I ran the project with ./gradlew bootRun

Project runs fine, it's just the code from: https://guides.gradle.org/building-spring-boot-2-projects-with-gradle/

Upon altering the code in, for example, HelloGradleController.java to return "Hello Gradle!!" there is no detection of file change or hot-reload.

Upon shutting down (Ctrl+C) and executing ./gradlew bootRun the project starts up and the changes are detected when I visit localhost:8080 once again.

bootRun prompt:

> Task :bootRun

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v2.1.7.RELEASE)

2019-08-09 11:04:01.080  INFO 4893 --- [  restartedMain] example.App                              : Starting App on ben-VirtualBox with PID 4893 (/home/ben/SpringBootProjects/gradle-spring-boot-project/build/classes/java/main started by ben in /home/ben/SpringBootProjects/gradle-spring-boot-project)
2019-08-09 11:04:01.083  INFO 4893 --- [  restartedMain] example.App                              : No active profile set, falling back to default profiles: default
2019-08-09 11:04:01.177  INFO 4893 --- [  restartedMain] .e.DevToolsPropertyDefaultsPostProcessor : Devtools property defaults active! Set 'spring.devtools.add-properties' to 'false' to disable
2019-08-09 11:04:01.178  INFO 4893 --- [  restartedMain] .e.DevToolsPropertyDefaultsPostProcessor : For additional web related logging consider setting the 'logging.level.web' property to 'DEBUG'
2019-08-09 11:04:02.806  INFO 4893 --- [  restartedMain] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8080 (http)
2019-08-09 11:04:02.856  INFO 4893 --- [  restartedMain] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2019-08-09 11:04:02.856  INFO 4893 --- [  restartedMain] org.apache.catalina.core.StandardEngine  : Starting Servlet engine: [Apache Tomcat/9.0.22]
2019-08-09 11:04:02.996  INFO 4893 --- [  restartedMain] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2019-08-09 11:04:02.996  INFO 4893 --- [  restartedMain] o.s.web.context.ContextLoader            : Root WebApplicationContext: initialization completed in 1818 ms
2019-08-09 11:04:03.272  INFO 4893 --- [  restartedMain] o.s.s.concurrent.ThreadPoolTaskExecutor  : Initializing ExecutorService 'applicationTaskExecutor'
2019-08-09 11:04:03.478  INFO 4893 --- [  restartedMain] o.s.b.d.a.OptionalLiveReloadServer       : LiveReload server is running on port 35729
2019-08-09 11:04:03.550  INFO 4893 --- [  restartedMain] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8080 (http) with context path ''
2019-08-09 11:04:03.560  INFO 4893 --- [  restartedMain] example.App                              : Started App in 2.994 seconds (JVM running for 3.488)
<=========----> 75% EXECUTING [9s]
> :bootRun

My build.gradle

/*
 * This file was generated by the Gradle 'init' task.
 *
 * This generated file contains a sample Java project to get you started.
 * For more details take a look at the Java Quickstart chapter in the Gradle
 * User Manual available at https://docs.gradle.org/5.5.1/userguide/tutorial_java_projects.html
 */

plugins {
    // Apply the java plugin to add support for Java
    id 'java'

    // Apply the application plugin to add support for building a CLI application
    id 'application'
    
    //https://guides.gradle.org/building-spring-boot-2-projects-with-gradle/
    id 'org.springframework.boot' version '2.1.7.RELEASE'
    id 'io.spring.dependency-management' version '1.0.8.RELEASE'
}


bootRun {
    sourceResources sourceSets.main
}


repositories {
    // Use jcenter for resolving dependencies.
    // You can declare any Maven/Ivy/file repository here.
    jcenter()
}

//https://docs.spring.io/spring-boot/docs/2.1.7.RELEASE/reference/html/using-boot-devtools.html
configurations {
   developmentOnly
   runtimeClasspath {
       extendsFrom developmentOnly
   }
}

dependencies {
    //compile('org.springframework.boot:spring-boot-devtools')
    developmentOnly('org.springframework.boot:spring-boot-devtools')

    // This dependency is used by the application.
    implementation 'com.google.guava:guava:27.1-jre'

    // Use JUnit test framework
    testImplementation 'junit:junit:4.12'

    //https://guides.gradle.org/building-spring-boot-2-projects-with-gradle/
    implementation 'org.springframework.boot:spring-boot-dependencies:2.1.7.RELEASE'
    implementation 'org.springframework.boot:spring-boot-starter-web'
    testImplementation 'org.springframework.boot:spring-boot-starter-test'
    components {
        withModule('org.springframework:spring-beans') {
            allVariants {
                withDependencyConstraints {
                    // Need to patch constraints because snakeyaml is an optional dependency
                    it.findAll { it.name == 'snakeyaml' }.each { it.version { strictly '1.19' } }
                }
            }
        }
    }
}

application {
    // Define the main class for the application
    mainClassName = 'example.App'
}

[snicoll]

You need to build the project for changed files to be copied on the classpath. See this section of the documentation.

[TheGitHubGuy1]

So there is no concept of hot-reload & auto recompile 'out of the box' with spring boot? that is, for example saving a change to a .java file won't be auto detected and classes won't be recompiled? There has to be some mechanism that updates the .class files, for example an IDE.

At that point springboot restarts the app on detection of .class file change?

[snicoll]

@benstuart Yes. If the section of the documentation I referenced doesn't make that crystal clear, feel free to submit a PR to suggest an improvement to it.

"out-of-the-box" is a vague term. Hot reload and restart is happening out-of-the-box, there is nothing in the documentation to my knowledge that touches the compilation part. And the section is also pretty focused on the IDE use case.

Having said all that, we're also discussing some potential improvements in that area for a future release of Spring Boot.

[TheGitHubGuy1]

@snicoll no worries, thanks for your time.

I had an assumption in my mind that spring boot CLI would work like node for example. But that was an assumption and the documentation doesn't explicitly say otherwise.

I come from a framework that does do auto recompile so it could just be my past experience affecting my expectations.

https://docs.spring.io/spring-boot/docs/2.1.7.RELEASE/gradle-plugin/reference/html/
Section 6.2 in my eyes gives the impression of auto recompile. Perhaps that can be clarified.

This closed ticket can give an indicator of others experiences, if others come along with the same query add a comment or a thumbs up.

[snicoll]

@benstuart This section is about "resources" (so web templates, css, etc. not code). This is good feedback, I've created #17851