Polish "Auto-configure Flyway with JavaMigration beans"

See spring-projectsgh-17993

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/flyway/FlywayAutoConfiguration.java

@@ -123,8 +123,8 @@ public Flyway flyway(FlywayProperties properties, DataSourceProperties dataSourc
 			configureCallbacks(configuration, orderedCallbacks);
 			fluentConfigurationCustomizers.orderedStream().forEach((customizer) -> customizer.customize(configuration));
 			configureFlywayCallbacks(configuration, orderedCallbacks);
-			JavaMigration[] migrations = javaMigrations.stream().toArray(JavaMigration[]::new);
-			configuration.javaMigrations(migrations);
+			List<JavaMigration> migrations = javaMigrations.stream().collect(Collectors.toList());
+			configureJavaMigrations(configuration, migrations);
 			return configuration.load();
 		}
 
@@ -218,6 +218,12 @@ private void configureFlywayCallbacks(FluentConfiguration flyway, List<Callback>
 			}
 		}
 
+		private void configureJavaMigrations(FluentConfiguration flyway, List<JavaMigration> migrations) {
+			if (!migrations.isEmpty()) {
+				flyway.javaMigrations(migrations.toArray(new JavaMigration[0]));
+			}
+		}
+
 		private String getProperty(Supplier<String> property, Supplier<String> defaultValue) {
 			String value = property.get();
 			return (value != null) ? value : defaultValue.get();

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/flyway/FlywayAutoConfigurationTests.java

@@ -482,77 +482,17 @@ DataSource flywayDataSource() {
 
 	}
 
-	@Configuration
-	protected static class FlywayJavaMigrationsConfiguration {
-
-		@Component
-		private static class Migration1 implements JavaMigration {
-
-			@Override
-			public MigrationVersion getVersion() {
-				return MigrationVersion.fromVersion("2");
-			}
-
-			@Override
-			public String getDescription() {
-				return "M1";
-			}
-
-			@Override
-			public Integer getChecksum() {
-				return 1;
-			}
-
-			@Override
-			public boolean isUndo() {
-				return false;
-			}
-
-			@Override
-			public boolean canExecuteInTransaction() {
-				return true;
-			}
-
-			@Override
-			public void migrate(org.flywaydb.core.api.migration.Context context) throws Exception {
-
-			}
+	@Configuration(proxyBeanMethods = false)
+	static class FlywayJavaMigrationsConfiguration {
 
+		@Bean
+		TestMigration migration1() {
+			return new TestMigration("2", "M1");
 		}
 
-		@Component
-		private static class Migration2 implements JavaMigration {
-
-			@Override
-			public MigrationVersion getVersion() {
-				return MigrationVersion.fromVersion("3");
-			}
-
-			@Override
-			public String getDescription() {
-				return "M2";
-			}
-
-			@Override
-			public Integer getChecksum() {
-				return 2;
-			}
-
-			@Override
-			public boolean isUndo() {
-				return false;
-			}
-
-			@Override
-			public boolean canExecuteInTransaction() {
-				return false;
-			}
-
-			@Override
-			public void migrate(org.flywaydb.core.api.migration.Context context) throws Exception {
-
-			}
-
+		@Bean
+		TestMigration migration2() {
+			return new TestMigration("3", "M2");
 		}
 
 	}
@@ -669,4 +609,47 @@ private CustomClassLoader(ClassLoader parent) {
 
 	}
 
+	private static final class TestMigration implements JavaMigration {
+
+		private final MigrationVersion version;
+
+		private final String description;
+
+		private TestMigration(String version, String description) {
+			this.version = MigrationVersion.fromVersion(version);
+			this.description = description;
+		}
+
+		@Override
+		public MigrationVersion getVersion() {
+			return this.version;
+		}
+
+		@Override
+		public String getDescription() {
+			return this.description;
+		}
+
+		@Override
+		public Integer getChecksum() {
+			return 1;
+		}
+
+		@Override
+		public boolean isUndo() {
+			return false;
+		}
+
+		@Override
+		public boolean canExecuteInTransaction() {
+			return true;
+		}
+
+		@Override
+		public void migrate(org.flywaydb.core.api.migration.Context context) {
+
+		}
+
+	}
+
 }

spring-boot-project/spring-boot-docs/src/main/asciidoc/howto.adoc

@@ -1907,7 +1907,7 @@ Spring Boot supports two higher-level migration tools: https://flywaydb.org/[Fly
 ==== Execute Flyway Database Migrations on Startup
 To automatically run Flyway database migrations on startup, add the `org.flywaydb:flyway-core` to your classpath.
 
-The migrations are scripts in the form `V<VERSION>__<NAME>.sql` (with `<VERSION>` an underscore-separated version, such as '`1`' or '`2_1`').
+Typically, migrations are scripts in the form `V<VERSION>__<NAME>.sql` (with `<VERSION>` an underscore-separated version, such as '`1`' or '`2_1`').
 By default, they are in a folder called `classpath:db/migration`, but you can modify that location by setting `spring.flyway.locations`.
 This is a comma-separated list of one or more `classpath:` or `filesystem:` locations.
 For example, the following configuration would search for scripts in both the default classpath location and the `/opt/migration` directory:
@@ -1928,6 +1928,8 @@ Assume the following:
 Rather than using `db/migration`, the preceding configuration sets the folder to use according to the type of the database (such as `db/migration/mysql` for MySQL).
 The list of supported databases is available in {sc-spring-boot}/jdbc/DatabaseDriver.{sc-ext}[`DatabaseDriver`].
 
+Migrations can also be written in Java. Flyway will be auto-configured with any beans that implement `JavaMigration`.
+
 {sc-spring-boot-autoconfigure}/flyway/FlywayProperties.{sc-ext}[`FlywayProperties`] provides most of Flyway's settings and a small set of additional properties that can be used to disable the migrations or switch off the location checking.
 If you need more control over the configuration, consider registering a `FlywayConfigurationCustomizer` bean.