Fork application process with Maven by default

Closes gh-16945

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

@@ -75,8 +75,7 @@ public abstract class AbstractRunMojo extends AbstractDependencyFilterMojo {
 	private boolean addResources = false;
 
 	/**
-	 * Path to agent jar. NOTE: the use of agents means that processes will be started by
-	 * forking a new JVM.
+	 * Path to agent jar. NOTE: a forked process is required to use this feature.
 	 * @since 1.0
 	 * @deprecated since 2.2.0 in favor of {@code agents}
 	 */
@@ -85,8 +84,7 @@ public abstract class AbstractRunMojo extends AbstractDependencyFilterMojo {
 	private File[] agent;
 
 	/**
-	 * Path to agent jars. NOTE: the use of agents means that processes will be started by
-	 * forking a new JVM.
+	 * Path to agent jars. NOTE: a forked process is required to use this feature.
 	 * @since 2.2
 	 */
 	@Parameter(property = "spring-boot.run.agents")
@@ -101,8 +99,7 @@ public abstract class AbstractRunMojo extends AbstractDependencyFilterMojo {
 
 	/**
 	 * Current working directory to use for the application. If not specified, basedir
-	 * will be used. NOTE: the use of working directory means that processes will be
-	 * started by forking a new JVM.
+	 * will be used. NOTE: a forked process is required to use this feature.
 	 * @since 1.5
 	 */
 	@Parameter(property = "spring-boot.run.workingDirectory")
@@ -111,16 +108,15 @@ public abstract class AbstractRunMojo extends AbstractDependencyFilterMojo {
 	/**
 	 * JVM arguments that should be associated with the forked process used to run the
 	 * application. On command line, make sure to wrap multiple values between quotes.
-	 * NOTE: the use of JVM arguments means that processes will be started by forking a
-	 * new JVM.
+	 * NOTE: a forked process is required to use this feature.
 	 * @since 1.1
 	 */
 	@Parameter(property = "spring-boot.run.jvmArguments")
 	private String jvmArguments;
 
 	/**
-	 * List of JVM system properties to pass to the process. NOTE: the use of system
-	 * properties means that processes will be started by forking a new JVM.
+	 * List of JVM system properties to pass to the process. NOTE: a forked process is
+	 * required to use this feature.
 	 * @since 2.1
 	 */
 	@Parameter
@@ -128,8 +124,8 @@ public abstract class AbstractRunMojo extends AbstractDependencyFilterMojo {
 
 	/**
 	 * List of Environment variables that should be associated with the forked process
-	 * used to run the application. NOTE: the use of Environment variables means that
-	 * processes will be started by forking a new JVM.
+	 * used to run the application. NOTE: a forked process is required to use this
+	 * feature.
 	 * @since 2.1
 	 */
 	@Parameter
@@ -177,13 +173,13 @@ public abstract class AbstractRunMojo extends AbstractDependencyFilterMojo {
 	private File classesDirectory;
 
 	/**
-	 * Flag to indicate if the run processes should be forked. {@code fork} is
-	 * automatically enabled if an agent, jvmArguments or working directory are specified,
-	 * or if devtools is present.
+	 * 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
 	 */
-	@Parameter(property = "spring-boot.run.fork")
-	private Boolean fork;
+	@Parameter(property = "spring-boot.run.fork", defaultValue = "true")
+	private boolean fork;
 
 	/**
 	 * Flag to include the test classpath when running.
@@ -213,15 +209,16 @@ public abstract class AbstractRunMojo extends AbstractDependencyFilterMojo {
 	 * @return {@code true} if the application process should be forked
 	 */
 	protected boolean isFork() {
-		return (Boolean.TRUE.equals(this.fork)
-				|| (this.fork == null && enableForkByDefault()));
+		return this.fork;
 	}
 
 	/**
 	 * Specify if fork should be enabled by default.
 	 * @return {@code true} if fork should be enabled by default
 	 * @see #logDisabledFork()
+	 * @deprecated as of 2.2.0 in favour of enabling forking by default.
 	 */
+	@Deprecated
 	protected boolean enableForkByDefault() {
 		return hasAgent() || hasJvmArgs() || hasEnvVariables()
 				|| hasWorkingDirectorySet();
@@ -264,7 +261,6 @@ public abstract class AbstractRunMojo extends AbstractDependencyFilterMojo {
 	/**
 	 * Log a warning indicating that fork mode has been explicitly disabled while some
 	 * conditions are present that require to enable it.
-	 * @see #enableForkByDefault()
 	 */
 	protected void logDisabledFork() {
 		if (getLog().isWarnEnabled()) {
@@ -273,9 +269,8 @@ public abstract class AbstractRunMojo extends AbstractDependencyFilterMojo {
 			}
 			if (hasJvmArgs()) {
 				RunArguments runArguments = resolveJvmArguments();
-				getLog().warn("Fork mode disabled, ignoring JVM argument(s) [" + Arrays
-						.stream(runArguments.asArray()).collect(Collectors.joining(" "))
-						+ "]");
+				getLog().warn("Fork mode disabled, ignoring JVM argument(s) ["
+						+ String.join(" ", runArguments.asArray()) + "]");
 			}
 			if (hasWorkingDirectorySet()) {
 				getLog().warn(

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

@@ -54,6 +54,7 @@ public class RunMojo extends AbstractRunMojo {
 	private Boolean hasDevtools;
 
 	@Override
+	@Deprecated
 	protected boolean enableForkByDefault() {
 		return super.enableForkByDefault() || hasDevtools();
 	}

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

@@ -67,8 +67,7 @@ public class StartMojo extends AbstractRunMojo {
 	private String jmxName = SpringApplicationAdminClient.DEFAULT_OBJECT_NAME;
 
 	/**
-	 * The port to use to expose the platform MBeanServer if the application needs to be
-	 * forked.
+	 * The port to use to expose the platform MBeanServer if the application is forked.
 	 */
 	@Parameter
 	private int jmxPort = 9001;