Fix check vendor location in FlywayAutoConfiguration

`flyway.locations` supports vendor resolution. But, if
`flyway.check-location=true` is added and there is just one location
with vendor location the current implementation fails. This commit adds
validation for vendor locations.

Author: eddumelendez

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

@@ -16,12 +16,12 @@
 
 package org.springframework.boot.autoconfigure.flyway;
 
+import java.util.Arrays;
 import java.util.Collections;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Set;
 
-import javax.annotation.PostConstruct;
 import javax.persistence.EntityManagerFactory;
 import javax.sql.DataSource;
 
@@ -104,6 +104,8 @@ public static class FlywayConfiguration {
 
 		private List<FlywayCallback> flywayCallbacks;
 
+		private static final String VENDOR_PLACEHOLDER = "{vendor}";
+
 		public FlywayConfiguration(FlywayProperties properties,
 				ResourceLoader resourceLoader, ObjectProvider<DataSource> dataSource,
 				@FlywayDataSource ObjectProvider<DataSource> flywayDataSource,
@@ -117,28 +119,6 @@ public FlywayConfiguration(FlywayProperties properties,
 			this.flywayCallbacks = flywayCallbacks.getIfAvailable(Collections::emptyList);
 		}
 
-		@PostConstruct
-		public void checkLocationExists() {
-			if (this.properties.isCheckLocation()) {
-				Assert.state(!this.properties.getLocations().isEmpty(),
-						"Migration script locations not configured");
-				boolean exists = hasAtLeastOneLocation();
-				Assert.state(exists,
-						() -> "Cannot find migrations location in: " + this.properties
-								.getLocations()
-						+ " (please add migrations or check your Flyway configuration)");
-			}
-		}
-
-		private boolean hasAtLeastOneLocation() {
-			for (String location : this.properties.getLocations()) {
-				if (this.resourceLoader.getResource(location).exists()) {
-					return true;
-				}
-			}
-			return false;
-		}
-
 		@Bean
 		@ConfigurationProperties(prefix = "spring.flyway")
 		public Flyway flyway() {
@@ -156,10 +136,61 @@ else if (this.flywayDataSource != null) {
 			}
 			flyway.setCallbacks(this.flywayCallbacks
 					.toArray(new FlywayCallback[this.flywayCallbacks.size()]));
-			flyway.setLocations(this.properties.getLocations().toArray(new String[0]));
+			String[] locations = resolveLocations(this.properties.getLocations().toArray(new String[0]), flyway.getDataSource());
+			checkLocationExists(locations);
+			flyway.setLocations(locations);
 			return flyway;
 		}
 
+		private static String[] resolveLocations(String[] locations, DataSource dataSource) {
+			if (usesVendorLocation(locations)) {
+				try {
+					String url = (String) JdbcUtils
+							.extractDatabaseMetaData(dataSource, "getURL");
+					DatabaseDriver vendor = DatabaseDriver.fromJdbcUrl(url);
+					if (vendor != DatabaseDriver.UNKNOWN) {
+						for (int i = 0; i < locations.length; i++) {
+							locations[i] = locations[i].replace(VENDOR_PLACEHOLDER,
+									vendor.getId());
+						}
+					}
+				}
+				catch (MetaDataAccessException ex) {
+					throw new IllegalStateException(ex);
+				}
+			}
+			return locations;
+		}
+
+		private static boolean usesVendorLocation(String... locations) {
+			for (String location : locations) {
+				if (location.contains(VENDOR_PLACEHOLDER)) {
+					return true;
+				}
+			}
+			return false;
+		}
+
+		private void checkLocationExists(String... locations) {
+			if (this.properties.isCheckLocation()) {
+				Assert.state(locations.length != 0,
+						"Migration script locations not configured");
+				boolean exists = hasAtLeastOneLocation(locations);
+				Assert.state(exists,
+						() -> "Cannot find migrations location in: " + Arrays.asList(locations)
+								+ " (please add migrations or check your Flyway configuration)");
+			}
+		}
+
+		private boolean hasAtLeastOneLocation(String... locations) {
+			for (String location : locations) {
+				if (this.resourceLoader.getResource(location).exists()) {
+					return true;
+				}
+			}
+			return false;
+		}
+
 		@Bean
 		@ConditionalOnMissingBean
 		public FlywayMigrationInitializer flywayInitializer(Flyway flyway) {
@@ -202,38 +233,13 @@ public FlywayJpaDependencyConfiguration() {
 
 	private static class SpringBootFlyway extends Flyway {
 
-		private static final String VENDOR_PLACEHOLDER = "{vendor}";
-
 		@Override
 		public void setLocations(String... locations) {
-			if (usesVendorLocation(locations)) {
-				try {
-					String url = (String) JdbcUtils
-							.extractDatabaseMetaData(getDataSource(), "getURL");
-					DatabaseDriver vendor = DatabaseDriver.fromJdbcUrl(url);
-					if (vendor != DatabaseDriver.UNKNOWN) {
-						for (int i = 0; i < locations.length; i++) {
-							locations[i] = locations[i].replace(VENDOR_PLACEHOLDER,
-									vendor.getId());
-						}
-					}
-				}
-				catch (MetaDataAccessException ex) {
-					throw new IllegalStateException(ex);
-				}
-			}
+			locations = FlywayConfiguration.resolveLocations(locations,
+					getDataSource());
 			super.setLocations(locations);
 		}
 
-		private boolean usesVendorLocation(String... locations) {
-			for (String location : locations) {
-				if (location.contains(VENDOR_PLACEHOLDER)) {
-					return true;
-				}
-			}
-			return false;
-		}
-
 	}
 
 	/**

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

@@ -255,6 +255,17 @@ public void useVendorDirectory() {
 				});
 	}
 
+	@Test
+	public void useOneLocationWithVendorDirectory() {
+		this.contextRunner.withUserConfiguration(EmbeddedDataSourceConfiguration.class)
+				.withPropertyValues("spring.flyway.locations=classpath:db/vendors/{vendor}")
+				.run((context) -> {
+					assertThat(context).hasSingleBean(Flyway.class);
+					Flyway flyway = context.getBean(Flyway.class);
+					assertThat(flyway.getLocations()).containsExactly("classpath:db/vendors/h2");
+				});
+	}
+
 	@Test
 	public void callbacksAreConfiguredAndOrdered() {
 		this.contextRunner.withUserConfiguration(EmbeddedDataSourceConfiguration.class,