Common root cause introspection algorithm in NestedExceptionUtils

Issue: SPR-15510

spring-core/src/main/java/org/springframework/core/NestedCheckedException.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2012 the original author or authors.
+ * Copyright 2002-2017 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.
@@ -80,13 +80,7 @@ public abstract class NestedCheckedException extends Exception {
 	 * @return the innermost exception, or {@code null} if none
 	 */
 	public Throwable getRootCause() {
-		Throwable rootCause = null;
-		Throwable cause = getCause();
-		while (cause != null && cause != rootCause) {
-			rootCause = cause;
-			cause = cause.getCause();
-		}
-		return rootCause;
+		return NestedExceptionUtils.getRootCause(this);
 	}
 
 	/**

spring-core/src/main/java/org/springframework/core/NestedExceptionUtils.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2008 the original author or authors.
+ * Copyright 2002-2017 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.
@@ -39,17 +39,48 @@ public abstract class NestedExceptionUtils {
 	 * @return the full exception message
 	 */
 	public static String buildMessage(String message, Throwable cause) {
-		if (cause != null) {
-			StringBuilder sb = new StringBuilder();
-			if (message != null) {
-				sb.append(message).append("; ");
-			}
-			sb.append("nested exception is ").append(cause);
-			return sb.toString();
-		}
-		else {
+		if (cause == null) {
 			return message;
 		}
+		StringBuilder sb = new StringBuilder(64);
+		if (message != null) {
+			sb.append(message).append("; ");
+		}
+		sb.append("nested exception is ").append(cause);
+		return sb.toString();
+	}
+
+	/**
+	 * Retrieve the innermost cause of the given exception, if any.
+	 * @param original the original exception to introspect
+	 * @return the innermost exception, or {@code null} if none
+	 * @since 4.3.9
+	 */
+	public static Throwable getRootCause(Throwable original) {
+		if (original == null) {
+			return null;
+		}
+		Throwable rootCause = null;
+		Throwable cause = original.getCause();
+		while (cause != null && cause != rootCause) {
+			rootCause = cause;
+			cause = cause.getCause();
+		}
+		return rootCause;
+	}
+
+	/**
+	 * Retrieve the most specific cause of the given exception, that is,
+	 * either the innermost cause (root cause) or the exception itself.
+	 * <p>Differs from {@link #getRootCause} in that it falls back
+	 * to the original exception if there is no root cause.
+	 * @param original the original exception to introspect
+	 * @return the most specific cause (never {@code null})
+	 * @since 4.3.9
+	 */
+	public static Throwable getMostSpecificCause(Throwable original) {
+		Throwable rootCause = getRootCause(original);
+		return (rootCause != null ? rootCause : original);
 	}
 
 }

spring-core/src/main/java/org/springframework/core/NestedRuntimeException.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2012 the original author or authors.
+ * Copyright 2002-2017 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.
@@ -81,13 +81,7 @@ public abstract class NestedRuntimeException extends RuntimeException {
 	 * @since 2.0
 	 */
 	public Throwable getRootCause() {
-		Throwable rootCause = null;
-		Throwable cause = getCause();
-		while (cause != null && cause != rootCause) {
-			rootCause = cause;
-			cause = cause.getCause();
-		}
-		return rootCause;
+		return NestedExceptionUtils.getRootCause(this);
 	}
 
 	/**