Don't rely on ConfigurationPropertyName exceptions

Update `ConfigurationPropertySourcesPropertySource` to no longer use
`try/catch` when checking for valid names. A new `isValid` method has
been introduced to `ConfigurationPropertyName` which is offers better
performance.

Fixes gh-9058

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

@@ -226,6 +226,45 @@ public final class ConfigurationPropertyName
 		return this;
 	}
 
+	/**
+	 * Returns if the given name is valid. If this method returns {@code true} then the
+	 * name may be used with {@link #of(String)} without throwing an exception.
+	 * @param name the name to test
+	 * @return {@code true} if the name is valid
+	 */
+	public static boolean isValid(String name) {
+		if (name == null) {
+			return false;
+		}
+		boolean indexed = false;
+		int charIndex = 0;
+		for (int i = 0; i < name.length(); i++) {
+			char ch = name.charAt(i);
+			if (!indexed) {
+				if (ch == '[') {
+					indexed = true;
+					charIndex = 1;
+				}
+				else if (ch == '.') {
+					charIndex = 0;
+				}
+				else {
+					if (!Element.isValid(charIndex, ch)) {
+						return false;
+					}
+					charIndex++;
+				}
+			}
+			else {
+				if (ch == ']') {
+					indexed = false;
+					charIndex = 0;
+				}
+			}
+		}
+		return true;
+	}
+
 	/**
 	 * Return a {@link ConfigurationPropertyName} for the specified string.
 	 * @param name the source name
@@ -335,7 +374,27 @@ public final class ConfigurationPropertyName
 			return this.value[form.ordinal()];
 		}
 
-		public static boolean isIndexed(String value) {
+		static boolean isValid(String value) {
+			if (!isIndexed(value)) {
+				for (int i = 0; i < value.length(); i++) {
+					if (!isValid(i, value.charAt(i))) {
+						return false;
+					}
+				}
+			}
+			return true;
+		}
+
+		static boolean isValid(int index, char ch) {
+			boolean isAlpha = ch >= 'a' && ch <= 'z';
+			boolean isNumeric = ch >= '0' && ch <= '9';
+			if (index == 0) {
+				return isAlpha;
+			}
+			return isAlpha || isNumeric || ch == '-';
+		}
+
+		private static boolean isIndexed(String value) {
 			return value.startsWith("[") && value.endsWith("]");
 		}
 

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

@@ -142,7 +142,6 @@ class ConfigurationPropertyNameBuilder {
 	 * An processor that will be applied to element values. Can be used to manipulate or
 	 * restrict the values that are used.
 	 */
-	@FunctionalInterface
 	public interface ElementValueProcessor {
 
 		/**
@@ -169,16 +168,9 @@ class ConfigurationPropertyNameBuilder {
 		default ElementValueProcessor withValidName() {
 			return (value) -> {
 				value = apply(value);
-				if (!Element.isIndexed(value)) {
-					for (int i = 0; i < value.length(); i++) {
-						char ch = value.charAt(i);
-						boolean isAlpha = ch >= 'a' && ch <= 'z';
-						boolean isNumeric = ch >= '0' && ch <= '9';
-						if (i == 0 && !isAlpha || !(isAlpha || isNumeric || ch == '-')) {
-							throw new IllegalArgumentException(
-									"Element value '" + value + "' is not valid");
-						}
-					}
+				if (!Element.isValid(value)) {
+					throw new IllegalArgumentException(
+							"Element value '" + value + "' is not valid");
 				}
 				return value;
 			};

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

@@ -56,11 +56,13 @@ class ConfigurationPropertySourcesPropertySource
 
 	private ConfigurationProperty findConfigurationProperty(String name) {
 		try {
-			return findConfigurationProperty(ConfigurationPropertyName.of(name));
+			if (ConfigurationPropertyName.isValid(name)) {
+				return findConfigurationProperty(ConfigurationPropertyName.of(name));
+			}
 		}
 		catch (Exception ex) {
-			return null;
 		}
+		return null;
 	}
 
 	private ConfigurationProperty findConfigurationProperty(

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

@@ -332,4 +332,24 @@ public class ConfigurationPropertyNameTests {
 		assertThat(name.append("foo").toString()).isEqualTo("foo");
 	}
 
+	@Test
+	public void isValidWhenValidShouldReturnTrue() throws Exception {
+		assertThat(ConfigurationPropertyName.isValid("")).isTrue();
+		assertThat(ConfigurationPropertyName.isValid("foo")).isTrue();
+		assertThat(ConfigurationPropertyName.isValid("foo.bar")).isTrue();
+		assertThat(ConfigurationPropertyName.isValid("foo[0]")).isTrue();
+		assertThat(ConfigurationPropertyName.isValid("foo[0].baz")).isTrue();
+		assertThat(ConfigurationPropertyName.isValid("foo.b1")).isTrue();
+		assertThat(ConfigurationPropertyName.isValid("foo.b-a-r")).isTrue();
+		assertThat(ConfigurationPropertyName.isValid("foo[FooBar].baz")).isTrue();
+	}
+
+	@Test
+	public void isValidWhenNotValidShouldReturnFalse() throws Exception {
+		assertThat(ConfigurationPropertyName.isValid(null)).isFalse();
+		assertThat(ConfigurationPropertyName.isValid("1foo")).isFalse();
+		assertThat(ConfigurationPropertyName.isValid("FooBar")).isFalse();
+		assertThat(ConfigurationPropertyName.isValid("foo!bar")).isFalse();
+	}
+
 }