Deprecate running an application in the Maven JVM

This commit deprecates the "fork" property so that the application
always runs in a dedicated process. This aligns with the behaviour of
the Gradle plugin, and simplifies the lifecycle of certain features that
would not work in a non-forked process.

Closes gh-30479

Author: snicoll

spring-boot-project/spring-boot-tools/spring-boot-maven-plugin/src/docs/asciidoc/running.adoc

@@ -9,13 +9,13 @@ The plugin includes a run goal which can be used to launch your application from
 
 Application arguments can be specified using the `arguments` parameter, see <<run.examples.using-application-arguments,using application arguments>> for more details.
 
-By default the application is executed in a forked process and setting properties on the command-line will not affect the application.
+The application is executed in a forked process and setting properties on the command-line will not affect the application.
 If you need to specify some JVM arguments (that is for debugging purposes), you can use the `jvmArguments` parameter, see <<run.examples.debug,Debug the application>> for more details.
 There is also explicit support for <<run.examples.system-properties,system properties>> and <<run.examples.environment-variables,environment variables>>.
 
 As enabling a profile is quite common, there is dedicated `profiles` property that offers a shortcut for `-Dspring-boot.run.jvmArguments="-Dspring.profiles.active=dev"`, see <<run.examples.specify-active-profiles,Specify active profiles>>.
 
-Although this is not recommended, it is possible to execute the application directly from the Maven JVM by disabling the `fork` property.
+Although this is not recommended (and deprecated), it is possible to execute the application directly from the Maven JVM by disabling the `fork` property.
 Doing so means that the `jvmArguments`, `systemPropertyVariables`, `environmentVariables` and `agents` options are ignored.
 
 Spring Boot `devtools` is a module to improve the development-time experience when working on Spring Boot applications.
@@ -73,7 +73,7 @@ include::goals/run.adoc[leveloffset=+1]
 
 [[run.examples.debug]]
 === Debug the Application
-By default, the `run` goal runs your application in a forked process.
+The `run` goal runs your application in a forked process.
 If you need to debug it, you should add the necessary JVM arguments to enable remote debugging.
 The following configuration suspend the process until a debugger has joined on port 5005:
 

spring-boot-project/spring-boot-tools/spring-boot-maven-plugin/src/main/java/org/springframework/boot/maven/AbstractRunMojo.java

@@ -192,12 +192,14 @@ public abstract class AbstractRunMojo extends AbstractDependencyFilterMojo {
 	private File classesDirectory;
 
 	/**
-	 * Flag to indicate if the run processes should be forked. Disabling forking will
-	 * disable some features such as an agent, custom JVM arguments, devtools or
-	 * specifying the working directory to use.
+	 * Deprecated. Flag to indicate if the run processes should be forked. Disabling
+	 * forking will disable some features such as an agent, custom JVM arguments, devtools
+	 * or specifying the working directory to use.
 	 * @since 1.2.0
+	 * @deprecated since 2.7.0 for removal in 3.0.0 with no replacement
 	 */
 	@Parameter(property = "spring-boot.run.fork", defaultValue = "true")
+	@Deprecated
 	private boolean fork;
 
 	/**
@@ -226,7 +228,9 @@ public void execute() throws MojoExecutionException, MojoFailureException {
 	/**
 	 * Specify if the application process should be forked.
 	 * @return {@code true} if the application process should be forked
+	 * @deprecated since 2.7.0 for removal in 3.0.0 with no replacement
 	 */
+	@Deprecated
 	protected boolean isFork() {
 		return this.fork;
 	}
@@ -244,6 +248,7 @@ private boolean hasWorkingDirectorySet() {
 		return this.workingDirectory != null;
 	}
 
+	@SuppressWarnings("deprecation")
 	private void run(String startClassName) throws MojoExecutionException, MojoFailureException {
 		boolean fork = isFork();
 		this.project.getProperties().setProperty("_spring.boot.fork.enabled", Boolean.toString(fork));
@@ -304,7 +309,9 @@ protected abstract void runWithForkedJvm(File workingDirectory, List<String> arg
 	 * @param arguments the class arguments
 	 * @throws MojoExecutionException in case of MOJO execution errors
 	 * @throws MojoFailureException in case of MOJO failures
+	 * @deprecated since 2.7.0 for removal in 3.0.0 with no replacement
 	 */
+	@Deprecated
 	protected abstract void runWithMavenJvm(String startClassName, String... arguments)
 			throws MojoExecutionException, MojoFailureException;
 

spring-boot-project/spring-boot-tools/spring-boot-maven-plugin/src/main/java/org/springframework/boot/maven/RunMojo.java

@@ -71,6 +71,7 @@ protected void logDisabledFork() {
 	}
 
 	@Override
+	@SuppressWarnings("deprecation")
 	protected RunArguments resolveJvmArguments() {
 		RunArguments jvmArguments = super.resolveJvmArguments();
 		if (isFork() && this.optimizedLaunch) {
@@ -114,6 +115,7 @@ private int forkJvm(File workingDirectory, List<String> args, Map<String, String
 	}
 
 	@Override
+	@Deprecated
 	protected void runWithMavenJvm(String startClassName, String... arguments) throws MojoExecutionException {
 		IsolatedThreadGroup threadGroup = new IsolatedThreadGroup(startClassName);
 		Thread launchThread = new Thread(threadGroup, new LaunchRunner(startClassName, arguments), "main");

spring-boot-project/spring-boot-tools/spring-boot-maven-plugin/src/main/java/org/springframework/boot/maven/StartMojo.java

@@ -113,6 +113,7 @@ private RunProcess runProcess(File workingDirectory, List<String> args, Map<Stri
 	}
 
 	@Override
+	@SuppressWarnings("deprecation")
 	protected RunArguments resolveApplicationArguments() {
 		RunArguments applicationArguments = super.resolveApplicationArguments();
 		applicationArguments.getArgs().addLast(ENABLE_MBEAN_PROPERTY);
@@ -123,6 +124,7 @@ protected RunArguments resolveApplicationArguments() {
 	}
 
 	@Override
+	@SuppressWarnings("deprecation")
 	protected RunArguments resolveJvmArguments() {
 		RunArguments jvmArguments = super.resolveJvmArguments();
 		if (isFork()) {
@@ -138,6 +140,7 @@ protected RunArguments resolveJvmArguments() {
 	}
 
 	@Override
+	@Deprecated
 	protected void runWithMavenJvm(String startClassName, String... arguments) throws MojoExecutionException {
 		IsolatedThreadGroup threadGroup = new IsolatedThreadGroup(startClassName);
 		Thread launchThread = new Thread(threadGroup, new LaunchRunner(startClassName, arguments),
@@ -171,6 +174,7 @@ private void waitForSpringApplication(long wait, int maxAttempts) throws MojoExe
 				"Spring application did not start before the configured timeout (" + (wait * maxAttempts) + "ms");
 	}
 
+	@SuppressWarnings("deprecation")
 	private void waitForSpringApplication() throws MojoFailureException, MojoExecutionException {
 		try {
 			if (isFork()) {