Bind to map with numeric key without needing []

Closes gh-10751

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/properties/source/ConfigurationPropertyName.java

@@ -29,7 +29,7 @@ import org.springframework.util.ObjectUtils;
 /**
  * A configuration property name composed of elements separated by dots. User created
  * names may contain the characters "{@code a-z}" "{@code 0-9}") and "{@code -}", they
- * must be lower-case and must start with a letter. The "{@code -}" is used purely for
+ * must be lower-case and must start with an alpha-numeric character. The "{@code -}" is used purely for
  * formatting, i.e. "{@code foo-bar}" and "{@code foobar}" are considered equivalent.
  * <p>
  * The "{@code [}" and "{@code ]}" characters may be used to indicate an associative
@@ -675,7 +675,7 @@ public final class ConfigurationPropertyName
 		}
 
 		public static boolean isValidChar(char ch, int index) {
-			return isAlpha(ch) || (index != 0 && (isNumeric(ch) || ch == '-'));
+			return isAlpha(ch) || isNumeric(ch) || (index != 0 && ch == '-');
 		}
 
 		private static boolean isAlpha(char ch) {

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/context/properties/ConfigurationPropertiesBindingPostProcessorTests.java

@@ -273,6 +273,20 @@ public class ConfigurationPropertiesBindingPostProcessorTests {
 		this.context.refresh();
 	}
 
+	@Test
+	public void bindToMapWithNumericKey() {
+		this.context = new AnnotationConfigApplicationContext();
+		MutablePropertySources sources = this.context.getEnvironment()
+				.getPropertySources();
+		Map<String, Object> source = new LinkedHashMap<>();
+		source.put("sample.foos.1.name", "One");
+		sources.addFirst(new MapPropertySource("test-source", source));
+		this.context.register(NumericKeyConfiguration.class);
+		this.context.refresh();
+		NumericKeyConfiguration foo = this.context.getBean(NumericKeyConfiguration.class);
+		assertThat(foo.getFoos().get("1")).isNotNull();
+	}
+
 	private void prepareConverterContext(Class<?>... config) {
 		this.context = new AnnotationConfigApplicationContext();
 		MutablePropertySources sources = this.context.getEnvironment()
@@ -604,4 +618,29 @@ public class ConfigurationPropertiesBindingPostProcessorTests {
 
 	}
 
+	@Configuration
+	@EnableConfigurationProperties
+	@ConfigurationProperties(prefix = "sample")
+	static class NumericKeyConfiguration {
+
+		private Map<String, Foo> foos = new LinkedHashMap<>();
+
+		public Map<String, Foo> getFoos() {
+			return this.foos;
+		}
+
+		static class Foo {
+
+			private String name;
+
+			public String getName() {
+				return this.name;
+			}
+
+			public void setName(String name) {
+				this.name = name;
+			}
+		}
+	}
+
 }

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/context/properties/source/ConfigurationPropertyNameTests.java

@@ -49,13 +49,6 @@ public class ConfigurationPropertyNameTests {
 		ConfigurationPropertyName.of(null);
 	}
 
-	@Test
-	public void ofNameShouldNotStartWithNumber() {
-		this.thrown.expect(InvalidConfigurationPropertyNameException.class);
-		this.thrown.expectMessage("is not valid");
-		ConfigurationPropertyName.of("1foo");
-	}
-
 	@Test
 	public void ofNameShouldNotStartWithDash() {
 		this.thrown.expect(InvalidConfigurationPropertyNameException.class);
@@ -107,6 +100,15 @@ public class ConfigurationPropertyNameTests {
 		assertThat(name.isIndexed(0)).isFalse();
 	}
 
+	@Test
+	public void ofNameWhenStartsWithNumber() {
+		ConfigurationPropertyName name = ConfigurationPropertyName.of("1foo");
+		assertThat(name.toString()).isEqualTo("1foo");
+		assertThat(name.getNumberOfElements()).isEqualTo(1);
+		assertThat(name.getElement(0, Form.ORIGINAL)).isEqualTo("1foo");
+		assertThat(name.isIndexed(0)).isFalse();
+	}
+
 	@Test
 	public void ofNameWhenRunOnAssociative() {
 		ConfigurationPropertyName name = ConfigurationPropertyName.of("foo[bar]");
@@ -420,8 +422,8 @@ public class ConfigurationPropertyNameTests {
 	@Test
 	public void appendWhenElementNameIsNotValidShouldThrowException() {
 		this.thrown.expect(InvalidConfigurationPropertyNameException.class);
-		this.thrown.expectMessage("Configuration property name '1bar' is not valid");
-		ConfigurationPropertyName.of("foo").append("1bar");
+		this.thrown.expectMessage("Configuration property name '-bar' is not valid");
+		ConfigurationPropertyName.of("foo").append("-bar");
 	}
 
 	@Test
@@ -589,7 +591,7 @@ public class ConfigurationPropertyNameTests {
 	@Test
 	public void isValidWhenNotValidShouldReturnFalse() {
 		assertThat(ConfigurationPropertyName.isValid(null)).isFalse();
-		assertThat(ConfigurationPropertyName.isValid("1foo")).isFalse();
+		assertThat(ConfigurationPropertyName.isValid("-foo")).isFalse();
 		assertThat(ConfigurationPropertyName.isValid("FooBar")).isFalse();
 		assertThat(ConfigurationPropertyName.isValid("foo!bar")).isFalse();
 	}