Use app…DefaultJvmArgs as convention for start script's defaultJvmOpts

Closes gh-12631

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/main/asciidoc/reacting.adoc

@@ -70,8 +70,10 @@ applied to a project, the Spring Boot plugin will automatically import the
 When Gradle's {application-plugin}[`application` plugin] is applied to a project, the
 Spring Boot plugin:
 
-1. Creates a `CreateStartScripts` task named `bootStartScripts` that will creates scripts
-   that launch the artifact in the `bootArchives` configuration using `java -jar`.
+1. Creates a `CreateStartScripts` task named `bootStartScripts` that will create scripts
+   that launch the artifact in the `bootArchives` configuration using `java -jar`. The
+   task is configured to use the `applicationDefaultJvmArgs` property as a convention
+   for its `defaultJvmOpts` property.
 2. Creates a new distribution named `boot` and configures it to contain the artifact in
    the `bootArchives` configuration in its `lib` directory and the start scripts in its
    `bin` directory.

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/main/java/org/springframework/boot/gradle/plugin/ApplicationPluginAction.java

@@ -77,6 +77,8 @@ final class ApplicationPluginAction implements PluginApplicationAction {
 				() -> new File(project.getBuildDir(), "bootScripts"));
 		bootStartScripts.getConventionMapping().map("applicationName",
 				applicationConvention::getApplicationName);
+		bootStartScripts.getConventionMapping().map("defaultJvmOpts",
+				applicationConvention::getApplicationDefaultJvmArgs);
 		CopySpec binCopySpec = project.copySpec().into("bin").from(bootStartScripts);
 		binCopySpec.setFileMode(0x755);
 		distribution.getContents().with(binCopySpec);

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/test/java/org/springframework/boot/gradle/plugin/ApplicationPluginActionIntegrationTests.java

@@ -73,6 +73,14 @@ public class ApplicationPluginActionIntegrationTests {
 						.contains("bootStartScripts exists = true");
 	}
 
+	@Test
+	public void createsBootStartScriptsTaskUsesApplicationPluginsDefaultJvmOpts() {
+		assertThat(this.gradleBuild
+				.build("startScriptsDefaultJvmOpts", "-PapplyApplicationPlugin")
+				.getOutput()).contains(
+						"bootStartScripts defaultJvmOpts = [-Dcom.example.a=alpha, -Dcom.example.b=bravo]");
+	}
+
 	@Test
 	public void zipDistributionForJarCanBeBuilt() throws IOException {
 		assertThat(

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/test/resources/org/springframework/boot/gradle/plugin/ApplicationPluginActionIntegrationTests.gradle

@@ -8,6 +8,7 @@ apply plugin: 'org.springframework.boot'
 
 if (project.hasProperty('applyApplicationPlugin')) {
 	apply plugin: 'application'
+	applicationDefaultJvmArgs = ['-Dcom.example.a=alpha', '-Dcom.example.b=bravo']
 }
 
 task('taskExists') {
@@ -31,3 +32,11 @@ task('javaCompileEncoding') {
 		}
 	}
 }
+
+task('startScriptsDefaultJvmOpts') {
+	doFirst {
+		tasks.withType(org.springframework.boot.gradle.tasks.application.CreateBootStartScripts) {
+			println "$name defaultJvmOpts = $defaultJvmOpts"
+		}
+	}
+}