Support for simple numeric Flyway version

While Flyway's `MigrationVersion` is a String value, a simple "0" is
also a valid number. When such value is not wrapped in YAML, an integer
is injected rather than a String which leads to a failure as we can't
convert it.

This commit updates the `StringToMigrationVersionConverter` to also
supports conversion from a Number. This is a convenience for users
using YAML for configuration

Closes gh-4981

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

 /*
- * Copyright 2012-2015 the original author or authors.
+ * Copyright 2012-2016 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -16,10 +16,15 @@
 
 package org.springframework.boot.autoconfigure.flyway;
 
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.Set;
+
 import javax.annotation.PostConstruct;
 import javax.persistence.EntityManagerFactory;
 import javax.sql.DataSource;
 
+import org.apache.commons.lang.ObjectUtils;
 import org.flywaydb.core.Flyway;
 import org.flywaydb.core.api.MigrationVersion;
 
@@ -38,7 +43,8 @@ import org.springframework.boot.context.properties.ConfigurationPropertiesBindin
 import org.springframework.boot.context.properties.EnableConfigurationProperties;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
-import org.springframework.core.convert.converter.Converter;
+import org.springframework.core.convert.TypeDescriptor;
+import org.springframework.core.convert.converter.GenericConverter;
 import org.springframework.core.io.DefaultResourceLoader;
 import org.springframework.core.io.ResourceLoader;
 import org.springframework.orm.jpa.AbstractEntityManagerFactoryBean;
@@ -63,8 +69,8 @@ public class FlywayAutoConfiguration {
 
 	@Bean
 	@ConfigurationPropertiesBinding
-	public StringToMigrationVersionConverter stringToMigrationVersionConverter() {
-		return new StringToMigrationVersionConverter();
+	public StringOrNumberToMigrationVersionConverter stringOrNumberMigrationVersionConverter() {
+		return new StringOrNumberToMigrationVersionConverter();
 	}
 
 	@Configuration
@@ -169,14 +175,29 @@ public class FlywayAutoConfiguration {
 	}
 
 	/**
-	 * Convert a String to a {@link MigrationVersion}.
+	 * Convert a String or Number to a {@link MigrationVersion}.
 	 */
-	private static class StringToMigrationVersionConverter
-			implements Converter<String, MigrationVersion> {
+	private static class StringOrNumberToMigrationVersionConverter
+			implements GenericConverter {
+
+		private static final Set<ConvertiblePair> CONVERTIBLE_PAIRS = createConvertiblePairs();
 
 		@Override
-		public MigrationVersion convert(String source) {
-			return MigrationVersion.fromVersion(source);
+		public Set<ConvertiblePair> getConvertibleTypes() {
+			return CONVERTIBLE_PAIRS;
+		}
+
+		@Override
+		public Object convert(Object source, TypeDescriptor sourceType, TypeDescriptor targetType) {
+			String value = ObjectUtils.toString(source);
+			return MigrationVersion.fromVersion(value);
+		}
+
+		private static Set<ConvertiblePair> createConvertiblePairs() {
+			Set<ConvertiblePair> convertiblePairs = new HashSet<ConvertiblePair>(2);
+			convertiblePairs.add(new ConvertiblePair(String.class, MigrationVersion.class));
+			convertiblePairs.add(new ConvertiblePair(Number.class, MigrationVersion.class));
+			return Collections.unmodifiableSet(convertiblePairs);
 		}
 
 	}

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

 /*
- * Copyright 2012-2015 the original author or authors.
+ * Copyright 2012-2016 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -17,6 +17,7 @@
 package org.springframework.boot.autoconfigure.flyway;
 
 import java.util.Arrays;
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.Map;
 
@@ -42,6 +43,7 @@ import org.springframework.context.annotation.AnnotationConfigApplicationContext
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.core.Ordered;
+import org.springframework.core.env.MapPropertySource;
 import org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean;
 import org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter;
 import org.springframework.stereotype.Component;
@@ -198,7 +200,7 @@ public class FlywayAutoConfigurationTests {
 	}
 
 	@Test
-	public void overrideBaselineVersion() throws Exception {
+	public void overrideBaselineVersionString() throws Exception {
 		EnvironmentTestUtils.addEnvironment(this.context, "flyway.baseline-version=0");
 		registerAndRefresh(EmbeddedDataSourceConfiguration.class,
 				FlywayAutoConfiguration.class,
@@ -208,6 +210,18 @@ public class FlywayAutoConfigurationTests {
 				equalTo(MigrationVersion.fromVersion("0")));
 	}
 
+	@Test
+	public void overrideBaselineVersionNumber() throws Exception {
+		Map<String, Object> source = Collections.<String, Object>singletonMap("flyway.baseline-version", 1);
+		this.context.getEnvironment().getPropertySources().addLast(new MapPropertySource("flyway", source));
+		registerAndRefresh(EmbeddedDataSourceConfiguration.class,
+				FlywayAutoConfiguration.class,
+				PropertyPlaceholderAutoConfiguration.class);
+		Flyway flyway = this.context.getBean(Flyway.class);
+		assertThat(flyway.getBaselineVersion(),
+				equalTo(MigrationVersion.fromVersion("1")));
+	}
+
 	private void registerAndRefresh(Class<?>... annotatedClasses) {
 		this.context.register(annotatedClasses);
 		this.context.refresh();