Replace deep exception message nesting with custom inclusion of cause messages

Includes deprecation of NestedServletException, whereas NestedCheckedException and NestedRuntimeException remain as base classes with several convenience methods.

Closes gh-25162

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

@@ -33,7 +33,6 @@ import org.springframework.lang.Nullable;
  * @author Rod Johnson
  * @author Juergen Hoeller
  * @see #getMessage
- * @see #printStackTrace
  * @see NestedRuntimeException
  */
 public abstract class NestedCheckedException extends Exception {
@@ -41,12 +40,6 @@ public abstract class NestedCheckedException extends Exception {
 	/** Use serialVersionUID from Spring 1.2 for interoperability. */
 	private static final long serialVersionUID = 7100714597678207546L;
 
-	static {
-		// Eagerly load the NestedExceptionUtils class to avoid classloader deadlock
-		// issues on OSGi when calling getMessage(). Reported by Don Brown; SPR-5607.
-		NestedExceptionUtils.class.getName();
-	}
-
 
 	/**
 	 * Construct a {@code NestedCheckedException} with the specified detail message.
@@ -67,17 +60,6 @@ public abstract class NestedCheckedException extends Exception {
 	}
 
 
-	/**
-	 * Return the detail message, including the message from the nested exception
-	 * if there is one.
-	 */
-	@Override
-	@Nullable
-	public String getMessage() {
-		return NestedExceptionUtils.buildMessage(super.getMessage(), getCause());
-	}
-
-
 	/**
 	 * Retrieve the innermost cause of this exception, if any.
 	 * @return the innermost exception, or {@code null} if none

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2022 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.
@@ -29,8 +29,6 @@ import org.springframework.lang.Nullable;
  * @since 2.0
  * @see NestedRuntimeException
  * @see NestedCheckedException
- * @see NestedIOException
- * @see org.springframework.web.util.NestedServletException
  */
 public abstract class NestedExceptionUtils {
 
@@ -39,7 +37,10 @@ public abstract class NestedExceptionUtils {
 	 * @param message the base message
 	 * @param cause the root cause
 	 * @return the full exception message
+	 * @deprecated as of 6.0, in favor of custom exception messages
+	 * with selective inclusion of cause messages
 	 */
+	@Deprecated
 	@Nullable
 	public static String buildMessage(@Nullable String message, @Nullable Throwable cause) {
 		if (cause == null) {

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

@@ -33,7 +33,6 @@ import org.springframework.lang.Nullable;
  * @author Rod Johnson
  * @author Juergen Hoeller
  * @see #getMessage
- * @see #printStackTrace
  * @see NestedCheckedException
  */
 public abstract class NestedRuntimeException extends RuntimeException {
@@ -41,12 +40,6 @@ public abstract class NestedRuntimeException extends RuntimeException {
 	/** Use serialVersionUID from Spring 1.2 for interoperability. */
 	private static final long serialVersionUID = 5439915454935047936L;
 
-	static {
-		// Eagerly load the NestedExceptionUtils class to avoid classloader deadlock
-		// issues on OSGi when calling getMessage(). Reported by Don Brown; SPR-5607.
-		NestedExceptionUtils.class.getName();
-	}
-
 
 	/**
 	 * Construct a {@code NestedRuntimeException} with the specified detail message.
@@ -67,17 +60,6 @@ public abstract class NestedRuntimeException extends RuntimeException {
 	}
 
 
-	/**
-	 * Return the detail message, including the message from the nested exception
-	 * if there is one.
-	 */
-	@Override
-	@Nullable
-	public String getMessage() {
-		return NestedExceptionUtils.buildMessage(super.getMessage(), getCause());
-	}
-
-
 	/**
 	 * Retrieve the innermost cause of this exception, if any.
 	 * @return the innermost exception, or {@code null} if none