Add useRandomPort

Closes gh-75

Author: rwinch

README.adoc

@@ -189,6 +189,23 @@ static CommonsExecWebServerFactoryBean authorizationServer() {
 When starting the remote debugger, it is important to remember that the classpath of the `CommonsExecWebServerFactoryBean` is independent of the project it runs in.
 This means, the classpath of the debugger will need to match the classpat of the `CommonsExecWebServerFactoryBean` rather than the project it exists in.
 
+=== Server Port
+
+By default `CommonsExecWebServerFactoryBean` starts the application on a random port by specifying the system property `server.port=0`.
+If you need to disable this behavior, you can opt out using the `useRandomPort` property as shown below:
+[source,java]
+----
+@Bean
+@OAuth2ClientProviderIssuerUri
+static CommonsExecWebServerFactoryBean authorizationServer() {
+	// @formatter:off
+	return CommonsExecWebServerFactoryBean.builder()
+		// ...
+		.useRandomPort(false);
+	// @formatter:on
+}
+----
+
 [[dynamicproperty]]
 == @DynamicProperty
 

spring-boot-testjars/src/main/java/org/springframework/experimental/boot/server/exec/CommonsExecWebServerFactoryBean.java

@@ -64,6 +64,8 @@ public class CommonsExecWebServerFactoryBean
 
 	private final DebugSettings debugSettings = new DebugSettings();
 
+	private boolean useRandomPort = true;
+
 	CommonsExecWebServerFactoryBean() {
 		Class<?> jarDetector = ClassUtils.resolveClassName(this.mainClass, null);
 		this.classpath.entries(new ResourceClasspathEntry(
@@ -113,6 +115,18 @@ public CommonsExecWebServerFactoryBean setAdditionalBeanClassNames(String... add
 				StringUtils.arrayToCommaDelimitedString(additionalBeanClassNames)));
 	}
 
+	/**
+	 * Sets if the Spring Boot application should be started on a random port. If true,
+	 * specifies the system property server.port=0 to start on a random port, else starts
+	 * on the port following standard Spring Boot rules.
+	 * @param useRandomPort true (default) if should start on random port, else false.
+	 * @return the {@link CommonsExecWebServerFactoryBean} for customization.
+	 */
+	public CommonsExecWebServerFactoryBean useRandomPort(boolean useRandomPort) {
+		this.useRandomPort = useRandomPort;
+		return this;
+	}
+
 	public CommonsExecWebServerFactoryBean systemProperties(Consumer<Map<String, String>> systemProperties) {
 		systemProperties.accept(this.systemProperties);
 		return this;
@@ -150,7 +164,7 @@ private CommonsExecWebServer build() {
 	private String[] createSystemPropertyArgs() {
 		Map<String, String> systemPropertyArgs = new HashMap<>(this.systemProperties);
 		systemPropertyArgs.put("PORTFILE", this.applicationPortFile.getAbsolutePath());
-		if (!systemPropertyArgs.containsKey("server.port")) {
+		if (this.useRandomPort) {
 			systemPropertyArgs.put("server.port", "0");
 		}
 		return systemPropertyArgs.entrySet().stream().map((e) -> "-D" + e.getKey() + "=" + e.getValue() + "")

spring-boot-testjars/src/test/java/org/springframework/experimental/boot/server/exec/CommonsExecWebServerFactoryBeanTests.java

@@ -105,12 +105,9 @@ void doesNotAddJarLauncherDetectorLauncherDetectorWhenMainClassDefined() throws
 	}
 
 	@Test
-	void serverPortWhenSpecifiedThenNotOverridden() throws Exception {
-		String expectedPort = "1234";
-		String portSystemProperty = "server.port";
-		CommonsExecWebServer server = CommonsExecWebServerFactoryBean.builder()
-				.systemProperties((props) -> props.put(portSystemProperty, expectedPort)).getObject();
-		assertThat(server.getCommandLine().getArguments()).contains("-D" + portSystemProperty + "=" + expectedPort);
+	void useRandomPortWhenFalseThenServerPortNot0() throws Exception {
+		CommonsExecWebServer server = CommonsExecWebServerFactoryBean.builder().useRandomPort(false).getObject();
+		assertThat(server.getCommandLine().getArguments()).doesNotContain("-Dserver.port=0");
 	}
 
 	// gh-53