Fix properties unicode value decoding

Fix a range error when checking for unicode hex chars.

Fixes spring-projectsgh-12716

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/env/OriginTrackedPropertiesLoader.java

@@ -224,17 +224,17 @@ private void readUnicode() throws IOException {
 			this.character = 0;
 			for (int i = 0; i < 4; i++) {
 				int digit = this.reader.read();
-				if (digit > -'0' && digit <= '9') {
+				if (digit >= '0' && digit <= '9') {
 					this.character = (this.character << 4) + digit - '0';
 				}
-				else if (digit > -'a' && digit <= 'f') {
+				else if (digit >= 'a' && digit <= 'f') {
 					this.character = (this.character << 4) + digit - 'a' + 10;
 				}
-				else if (digit > -'A' && digit <= 'F') {
+				else if (digit >= 'A' && digit <= 'F') {
 					this.character = (this.character << 4) + digit - 'A' + 10;
 				}
 				else {
-					throw new IllegalArgumentException("Malformed \\uxxxx encoding.");
+					throw new IllegalStateException("Malformed \\uxxxx encoding.");
 				}
 			}
 		}

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/env/OriginTrackedPropertiesLoaderTests.java

@@ -20,7 +20,9 @@
 import java.util.Properties;
 
 import org.junit.Before;
+import org.junit.Rule;
 import org.junit.Test;
+import org.junit.rules.ExpectedException;
 
 import org.springframework.boot.origin.OriginTrackedValue;
 import org.springframework.boot.origin.TextResourceOrigin;
@@ -37,6 +39,9 @@
  */
 public class OriginTrackedPropertiesLoaderTests {
 
+	@Rule
+	public ExpectedException thrown = ExpectedException.none();
+
 	private ClassPathResource resource;
 
 	private Map<String, OriginTrackedValue> properties;
@@ -85,6 +90,15 @@ public void getUnicodeProperty() {
 		assertThat(getLocation(value)).isEqualTo("12:14");
 	}
 
+	@Test
+	public void getMalformedUnicodeProperty() throws Exception {
+		// gh-2716
+		this.thrown.expect(IllegalStateException.class);
+		this.thrown.expectMessage("Malformed \\uxxxx encoding");
+		new OriginTrackedPropertiesLoader(new ClassPathResource(
+				"test-properties-malformed-unicode.properties", getClass())).load();
+	}
+
 	@Test
 	public void getEscapedProperty() {
 		OriginTrackedValue value = this.properties.get("test=property");

spring-boot-project/spring-boot/src/test/resources/org/springframework/boot/env/test-properties-malformed-unicode.properties

@@ -0,0 +1 @@
+test-malformed-unicode=properties\u(026test