Allow override of pidfile location

The file name can now be overridden at runtime with a System property or
environment variable named "PIDFILE" (or "pidfile").

Fixes gh-1579

spring-boot-actuator/src/main/java/org/springframework/boot/actuate/system/ApplicationPidListener.java

@@ -26,10 +26,13 @@ import org.springframework.boot.context.event.ApplicationStartedEvent;
 import org.springframework.context.ApplicationListener;
 import org.springframework.core.Ordered;
 import org.springframework.util.Assert;
+import org.springframework.util.SystemPropertyUtils;
 
 /**
  * An {@link org.springframework.context.ApplicationListener} that saves application PID
- * into file. This application listener will be triggered exactly once per JVM.
+ * into file. This application listener will be triggered exactly once per JVM, and the file
+ * name can be overridden at runtime with a System property or environment variable named
+ * "PIDFILE" (or "pidfile").
  *
  * @author Jakub Kubrynski
  * @author Dave Syer
@@ -62,8 +65,7 @@ public class ApplicationPidListener implements
 	 * @param filename the name of file containing pid
 	 */
 	public ApplicationPidListener(String filename) {
-		Assert.notNull(filename, "Filename must not be null");
-		this.file = new File(filename);
+		this(new File(filename));
 	}
 
 	/**
@@ -72,7 +74,10 @@ public class ApplicationPidListener implements
 	 */
 	public ApplicationPidListener(File file) {
 		Assert.notNull(file, "File must not be null");
-		this.file = file;
+		String actual = SystemPropertyUtils.resolvePlaceholders("${PIDFILE}", true);
+		actual = !actual.contains("$") ? actual :  SystemPropertyUtils.resolvePlaceholders("${pidfile}", true);
+		actual = !actual.contains("$") ? actual :  file.getAbsolutePath();
+		this.file = new File(actual);
 	}
 
 	@Override

spring-boot-actuator/src/test/java/org/springframework/boot/actuate/system/ApplicationPidListenerTests.java

@@ -33,12 +33,12 @@ import static org.hamcrest.Matchers.not;
 import static org.junit.Assert.assertThat;
 
 /**
- * Tests fpr {@link ApplicationPidListener}.
+ * Tests for {@link ApplicationPidListener}.
  *
  * @author Jakub Kubrynski
  * @author Dave Syer
  */
-public class ApplicationPidListenerTest {
+public class ApplicationPidListenerTests {
 
 	private static final ApplicationStartedEvent EVENT = new ApplicationStartedEvent(
 			new SpringApplication(), new String[] {});
@@ -49,6 +49,7 @@ public class ApplicationPidListenerTest {
 	@Before
 	@After
 	public void resetListener() {
+		System.clearProperty("PIDFILE");
 		ApplicationPidListener.reset();
 	}
 
@@ -60,4 +61,13 @@ public class ApplicationPidListenerTest {
 		assertThat(FileCopyUtils.copyToString(new FileReader(file)), not(isEmptyString()));
 	}
 
+	@Test
+	public void overridePidFile() throws Exception {
+		File file = this.temporaryFolder.newFile();
+		System.setProperty("PIDFILE", this.temporaryFolder.newFile().getAbsolutePath());
+		ApplicationPidListener listener = new ApplicationPidListener(file);
+		listener.onApplicationEvent(EVENT);
+		assertThat(FileCopyUtils.copyToString(new FileReader(System.getProperty("PIDFILE"))), not(isEmptyString()));
+	}
+
 }

spring-boot/src/main/java/org/springframework/boot/context/event/ApplicationStartedEvent.java

@@ -34,7 +34,7 @@ public class ApplicationStartedEvent extends SpringApplicationEvent {
 
 	/**
 	 * @param application the current application
-	 * @param args the argumemts the application is running with
+	 * @param args the arguments the application is running with
 	 */
 	public ApplicationStartedEvent(SpringApplication application, String[] args) {
 		super(application, args);