Turn LivenessState and ReadinessState into enums

Prior to this commit, `LivenessState` and `ReadinessState` were
immutable classes. This was done in order to have additional behavior
and information in those classes.

Because the current implementation doesn't need this, this commit turns
those classes into simple enums.
Additional state and information can be added to the
`*StateChangedEvent` classes.

See gh-19593

spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/availability/LivenessProbeHealthIndicator.java

@@ -38,7 +38,7 @@ public class LivenessProbeHealthIndicator extends AbstractHealthIndicator {
 
 	@Override
 	protected void doHealthCheck(Health.Builder builder) throws Exception {
-		if (LivenessState.live().equals(this.applicationAvailabilityProvider.getLivenessState())) {
+		if (LivenessState.LIVE.equals(this.applicationAvailabilityProvider.getLivenessState())) {
 			builder.up();
 		}
 		else {

spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/availability/ReadinessProbeHealthIndicator.java

@@ -38,7 +38,7 @@ public class ReadinessProbeHealthIndicator extends AbstractHealthIndicator {
 
 	@Override
 	protected void doHealthCheck(Health.Builder builder) throws Exception {
-		if (ReadinessState.ready().equals(this.applicationAvailabilityProvider.getReadinessState())) {
+		if (ReadinessState.READY.equals(this.applicationAvailabilityProvider.getReadinessState())) {
 			builder.up();
 		}
 		else {

spring-boot-project/spring-boot-actuator/src/test/java/org/springframework/boot/actuate/availability/LivenessProbeHealthIndicatorTests.java

@@ -46,13 +46,13 @@ class LivenessProbeHealthIndicatorTests {
 
 	@Test
 	void livenessIsLive() {
-		when(this.stateProvider.getLivenessState()).thenReturn(LivenessState.live());
+		when(this.stateProvider.getLivenessState()).thenReturn(LivenessState.LIVE);
 		assertThat(this.healthIndicator.health().getStatus()).isEqualTo(Status.UP);
 	}
 
 	@Test
 	void livenessIsBroken() {
-		when(this.stateProvider.getLivenessState()).thenReturn(LivenessState.broken());
+		when(this.stateProvider.getLivenessState()).thenReturn(LivenessState.BROKEN);
 		assertThat(this.healthIndicator.health().getStatus()).isEqualTo(Status.DOWN);
 	}
 

spring-boot-project/spring-boot-actuator/src/test/java/org/springframework/boot/actuate/availability/ReadinessProbeHealthIndicatorTests.java

@@ -46,13 +46,13 @@ class ReadinessProbeHealthIndicatorTests {
 
 	@Test
 	void readinessIsReady() {
-		when(this.stateProvider.getReadinessState()).thenReturn(ReadinessState.ready());
+		when(this.stateProvider.getReadinessState()).thenReturn(ReadinessState.READY);
 		assertThat(this.healthIndicator.health().getStatus()).isEqualTo(Status.UP);
 	}
 
 	@Test
 	void readinessIsUnready() {
-		when(this.stateProvider.getReadinessState()).thenReturn(ReadinessState.unready());
+		when(this.stateProvider.getReadinessState()).thenReturn(ReadinessState.UNREADY);
 		assertThat(this.healthIndicator.health().getStatus()).isEqualTo(Status.OUT_OF_SERVICE);
 	}
 

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/availability/ApplicationAvailabilityProvider.java

@@ -39,10 +39,10 @@ public class ApplicationAvailabilityProvider implements ApplicationListener<Appl
 
 	/**
 	 * Create a new {@link ApplicationAvailabilityProvider} instance with
-	 * {@link LivenessState#broken()} and {@link ReadinessState#unready()}.
+	 * {@link LivenessState#BROKEN} and {@link ReadinessState#UNREADY}.
 	 */
 	public ApplicationAvailabilityProvider() {
-		this(LivenessState.broken(), ReadinessState.unready());
+		this(LivenessState.BROKEN, ReadinessState.UNREADY);
 	}
 
 	/**

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/availability/LivenessState.java

@@ -16,8 +16,6 @@
 
 package org.springframework.boot.availability;
 
-import java.util.Objects;
-
 /**
  * "Liveness" state of the application.
  * <p>
@@ -28,59 +26,16 @@ import java.util.Objects;
  * @author Brian Clozel
  * @since 2.3.0
  */
-public final class LivenessState {
+public enum LivenessState {
 
-	private final Status status;
+	/**
+	 * The application is running and its internal state is correct.
+	 */
+	LIVE,
 
-	LivenessState(Status status) {
+	/**
-		this.status = status;
+	 * The internal state of the application is broken.
-	}
+	 */
-
+	BROKEN
-	public Status getStatus() {
-		return this.status;
-	}
-
-	@Override
-	public boolean equals(Object obj) {
-		if (this == obj) {
-			return true;
-		}
-		if (obj == null || getClass() != obj.getClass()) {
-			return false;
-		}
-		return this.status == ((LivenessState) obj).status;
-	}
-
-	@Override
-	public int hashCode() {
-		return Objects.hash(this.status);
-	}
-
-	@Override
-	public String toString() {
-		return "LivenessState{" + "status=" + this.status + '}';
-	}
-
-	public static LivenessState broken() {
-		return new LivenessState(Status.BROKEN);
-	}
-
-	public static LivenessState live() {
-		return new LivenessState(Status.LIVE);
-	}
-
-	public enum Status {
-
-		/**
-		 * The application is running and its internal state is correct.
-		 */
-		LIVE,
-
-		/**
-		 * The internal state of the application is broken.
-		 */
-		BROKEN
-
-	}
 
 }

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/availability/LivenessStateChangedEvent.java

@@ -47,7 +47,7 @@ public class LivenessStateChangedEvent extends ApplicationEvent {
 	 * @return the application event
 	 */
 	public static LivenessStateChangedEvent live(String cause) {
-		return new LivenessStateChangedEvent(LivenessState.live(), cause);
+		return new LivenessStateChangedEvent(LivenessState.LIVE, cause);
 	}
 
 	/**
@@ -57,7 +57,7 @@ public class LivenessStateChangedEvent extends ApplicationEvent {
 	 * @return the application event
 	 */
 	public static LivenessStateChangedEvent broken(String cause) {
-		return new LivenessStateChangedEvent(LivenessState.broken(), cause);
+		return new LivenessStateChangedEvent(LivenessState.BROKEN, cause);
 	}
 
 	/**
@@ -68,7 +68,7 @@ public class LivenessStateChangedEvent extends ApplicationEvent {
 	 * @return the application event
 	 */
 	public static LivenessStateChangedEvent broken(Throwable throwable) {
-		return new LivenessStateChangedEvent(LivenessState.broken(), throwable.getMessage());
+		return new LivenessStateChangedEvent(LivenessState.BROKEN, throwable.getMessage());
 	}
 
 }

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/availability/ReadinessState.java

@@ -16,8 +16,6 @@
 
 package org.springframework.boot.availability;
 
-import java.util.Objects;
-
 /**
  * "Readiness" state of the application.
  * <p>
@@ -28,59 +26,16 @@ import java.util.Objects;
  * @author Brian Clozel
  * @since 2.3.0
  */
-public final class ReadinessState {
+public enum ReadinessState {
 
-	private final Availability availability;
+	/**
+	 * The application is not willing to receive traffic.
+	 */
+	UNREADY,
 
-	private ReadinessState(Availability availability) {
+	/**
-		this.availability = availability;
+	 * The application is ready to receive traffic.
-	}
+	 */
-
+	READY
-	public Availability getAvailability() {
-		return this.availability;
-	}
-
-	@Override
-	public boolean equals(Object obj) {
-		if (this == obj) {
-			return true;
-		}
-		if (obj == null || getClass() != obj.getClass()) {
-			return false;
-		}
-		return this.availability == ((ReadinessState) obj).availability;
-	}
-
-	@Override
-	public int hashCode() {
-		return Objects.hash(this.availability);
-	}
-
-	@Override
-	public String toString() {
-		return "ReadinessState{" + "availability=" + this.availability + '}';
-	}
-
-	public static ReadinessState ready() {
-		return new ReadinessState(Availability.READY);
-	}
-
-	public static ReadinessState unready() {
-		return new ReadinessState(Availability.UNREADY);
-	}
-
-	public enum Availability {
-
-		/**
-		 * The application is not willing to receive traffic.
-		 */
-		UNREADY,
-
-		/**
-		 * The application is ready to receive traffic.
-		 */
-		READY
-
-	}
 
 }

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/availability/ReadinessStateChangedEvent.java

@@ -43,7 +43,7 @@ public class ReadinessStateChangedEvent extends ApplicationEvent {
 	 * @return the application event
 	 */
 	public static ReadinessStateChangedEvent ready() {
-		return new ReadinessStateChangedEvent(ReadinessState.ready());
+		return new ReadinessStateChangedEvent(ReadinessState.READY);
 	}
 
 	/**
@@ -52,7 +52,7 @@ public class ReadinessStateChangedEvent extends ApplicationEvent {
 	 * @return the application event
 	 */
 	public static ReadinessStateChangedEvent unready() {
-		return new ReadinessStateChangedEvent(ReadinessState.unready());
+		return new ReadinessStateChangedEvent(ReadinessState.UNREADY);
 	}
 
 }

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/availability/ApplicationAvailabilityProviderTests.java

@@ -30,14 +30,14 @@ class ApplicationAvailabilityProviderTests {
 	@Test
 	void initialStateShouldBeFailures() {
 		ApplicationAvailabilityProvider stateProvider = new ApplicationAvailabilityProvider();
-		assertThat(stateProvider.getLivenessState()).isEqualTo(LivenessState.broken());
+		assertThat(stateProvider.getLivenessState()).isEqualTo(LivenessState.BROKEN);
-		assertThat(stateProvider.getReadinessState()).isEqualTo(ReadinessState.unready());
+		assertThat(stateProvider.getReadinessState()).isEqualTo(ReadinessState.UNREADY);
 	}
 
 	@Test
 	void updateLivenessState() {
 		ApplicationAvailabilityProvider stateProvider = new ApplicationAvailabilityProvider();
-		LivenessState livenessState = LivenessState.live();
+		LivenessState livenessState = LivenessState.LIVE;
 		stateProvider.onApplicationEvent(new LivenessStateChangedEvent(livenessState, "Startup complete"));
 		assertThat(stateProvider.getLivenessState()).isEqualTo(livenessState);
 	}
@@ -46,7 +46,7 @@ class ApplicationAvailabilityProviderTests {
 	void updateReadiessState() {
 		ApplicationAvailabilityProvider stateProvider = new ApplicationAvailabilityProvider();
 		stateProvider.onApplicationEvent(ReadinessStateChangedEvent.ready());
-		assertThat(stateProvider.getReadinessState()).isEqualTo(ReadinessState.ready());
+		assertThat(stateProvider.getReadinessState()).isEqualTo(ReadinessState.READY);
 	}
 
 }