Add support for dumping the heap on OpenJ9

Closes gh-26466

spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/management/HeapDumpWebEndpoint.java

@@ -100,25 +100,37 @@ public class HeapDumpWebEndpoint {
 		if (this.heapDumper == null) {
 			this.heapDumper = createHeapDumper();
 		}
-		File file = createTempFile(live);
+		File file = createTempFile();
 		this.heapDumper.dumpHeap(file, live);
 		return new TemporaryFileSystemResource(file);
 	}
 
-	private File createTempFile(boolean live) throws IOException {
+	private File createTempFile() throws IOException {
 		String date = DateTimeFormatter.ofPattern("yyyy-MM-dd-HH-mm").format(LocalDateTime.now());
-		File file = File.createTempFile("heapdump" + date + (live ? "-live" : ""), ".hprof");
+		File file = File.createTempFile("heap-" + date, "." + determineDumpSuffix());
 		file.delete();
 		return file;
 	}
 
+	private String determineDumpSuffix() {
+		if (this.heapDumper instanceof OpenJ9DiagnosticsMXBeanHeapDumper) {
+			return "phd";
+		}
+		return "hprof";
+	}
+
 	/**
 	 * Factory method used to create the {@link HeapDumper}.
 	 * @return the heap dumper to use
 	 * @throws HeapDumperUnavailableException if the heap dumper cannot be created
 	 */
 	protected HeapDumper createHeapDumper() throws HeapDumperUnavailableException {
-		return new HotSpotDiagnosticMXBeanHeapDumper();
+		try {
+			return new HotSpotDiagnosticMXBeanHeapDumper();
+		}
+		catch (HeapDumperUnavailableException ex) {
+			return new OpenJ9DiagnosticsMXBeanHeapDumper();
+		}
 	}
 
 	/**
@@ -140,8 +152,8 @@ public class HeapDumpWebEndpoint {
 	}
 
 	/**
-	 * {@link HeapDumper} that uses {@code com.sun.management.HotSpotDiagnosticMXBean}
-	 * available on Oracle and OpenJDK to dump the heap to a file.
+	 * {@link HeapDumper} that uses {@code com.sun.management.HotSpotDiagnosticMXBean},
+	 * available on Oracle and OpenJDK, to dump the heap to a file.
 	 */
 	protected static class HotSpotDiagnosticMXBeanHeapDumper implements HeapDumper {
 
@@ -171,6 +183,38 @@ public class HeapDumpWebEndpoint {
 
 	}
 
+	/**
+	 * {@link HeapDumper} that uses
+	 * {@code openj9.lang.management.OpenJ9DiagnosticsMXBean}, available on OpenJ9, to
+	 * dump the heap to a file.
+	 */
+	private static final class OpenJ9DiagnosticsMXBeanHeapDumper implements HeapDumper {
+
+		private Object diagnosticMXBean;
+
+		private Method dumpHeapMethod;
+
+		@SuppressWarnings("unchecked")
+		private OpenJ9DiagnosticsMXBeanHeapDumper() {
+			try {
+				Class<?> mxBeanClass = ClassUtils.resolveClassName("openj9.lang.management.OpenJ9DiagnosticsMXBean",
+						null);
+				this.diagnosticMXBean = ManagementFactory.getPlatformMXBean((Class<PlatformManagedObject>) mxBeanClass);
+				this.dumpHeapMethod = ReflectionUtils.findMethod(mxBeanClass, "triggerDumpToFile", String.class,
+						String.class);
+			}
+			catch (Throwable ex) {
+				throw new HeapDumperUnavailableException("Unable to locate OpenJ9DiagnosticsMXBean", ex);
+			}
+		}
+
+		@Override
+		public void dumpHeap(File file, boolean live) throws IOException, InterruptedException {
+			ReflectionUtils.invokeMethod(this.dumpHeapMethod, this.diagnosticMXBean, "heap", file.getAbsolutePath());
+		}
+
+	}
+
 	/**
 	 * Exception to be thrown if the {@link HeapDumper} cannot be created.
 	 */