Return -1 port for non-listening WebServers

Update `WebServer` implementations to return -1 from `getPort()` if
the server  isn't listening on a port. This aligns the implementations
with the interface Javadoc.

See gh-24606

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/embedded/jetty/JettyWebServer.java

@@ -275,11 +275,13 @@ public void stop() {
 	@Override
 	public int getPort() {
 		Connector[] connectors = this.server.getConnectors();
+		Integer localPort = -1;
 		for (Connector connector : connectors) {
 			// Probably only one...
-			return getLocalPort(connector);
+			localPort = getLocalPort(connector);
+			break;
 		}
-		return 0;
+		return (localPort > 0) ? localPort : -1;
 	}
 
 	@Override

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/embedded/netty/NettyWebServer.java

@@ -192,7 +192,7 @@ public int getPort() {
 		if (this.disposableServer != null) {
 			return this.disposableServer.port();
 		}
-		return 0;
+		return -1;
 	}
 
 }

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/embedded/tomcat/TomcatWebServer.java

@@ -364,7 +364,7 @@ public int getPort() {
 		if (connector != null) {
 			return connector.getLocalPort();
 		}
-		return 0;
+		return -1;
 	}
 
 	private String getContextPath() {

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/embedded/undertow/UndertowWebServer.java

@@ -295,7 +295,7 @@ public void stop() throws WebServerException {
 	public int getPort() {
 		List<Port> ports = getActualPorts();
 		if (ports.isEmpty()) {
-			return 0;
+			return -1;
 		}
 		return ports.get(0).getNumber();
 	}

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/web/reactive/server/AbstractReactiveWebServerFactoryTests.java

@@ -115,6 +115,16 @@ void specificPort() throws Exception {
 		assertThat(this.webServer.getPort()).isEqualTo(specificPort);
 	}
 
+	@Test
+	void portIsMinusOneWhenConnectionIsClosed() {
+		AbstractReactiveWebServerFactory factory = getFactory();
+		this.webServer = factory.getWebServer(new EchoHandler());
+		this.webServer.start();
+		assertThat(this.webServer.getPort()).isGreaterThan(0);
+		this.webServer.stop();
+		assertThat(this.webServer.getPort()).isEqualTo(-1);
+	}
+
 	@Test
 	void basicSslFromClassPath() {
 		testBasicSslWithKeyStore("classpath:test.jks", "password");

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/web/servlet/server/AbstractServletWebServerFactoryTests.java

@@ -250,7 +250,7 @@ void emptyServerWhenPortIsMinusOne() {
 		factory.setPort(-1);
 		this.webServer = factory.getWebServer(exampleServletRegistration());
 		this.webServer.start();
-		assertThat(this.webServer.getPort()).isLessThan(0); // Jetty is -2
+		assertThat(this.webServer.getPort()).isEqualTo(-1);
 	}
 
 	@Test
@@ -300,6 +300,16 @@ void loadOnStartAfterContextIsInitialized() {
 		assertThat(servlet.getInitCount()).isEqualTo(1);
 	}
 
+	@Test
+	void portIsMinusOneWhenConnectionIsClosed() {
+		AbstractServletWebServerFactory factory = getFactory();
+		this.webServer = factory.getWebServer();
+		this.webServer.start();
+		assertThat(this.webServer.getPort()).isGreaterThan(0);
+		this.webServer.stop();
+		assertThat(this.webServer.getPort()).isEqualTo(-1);
+	}
+
 	@Test
 	void specificPort() throws Exception {
 		AbstractServletWebServerFactory factory = getFactory();