Common root cause introspection algorithm in NestedExceptionUtils

Issue: SPR-15510
(cherry picked from commit 9d8e9cf)

Author: jhoeller

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 String getMessage() {
 	 * @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 String getMessage() {
 	 * @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);
 	}
 
 	/**

spring-websocket/src/main/java/org/springframework/web/socket/sockjs/transport/session/AbstractSockJsSession.java

@@ -19,7 +19,6 @@
 import java.io.IOException;
 import java.util.ArrayList;
 import java.util.Arrays;
-import java.util.Collections;
 import java.util.Date;
 import java.util.HashSet;
 import java.util.List;
@@ -31,7 +30,7 @@
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
 
-import org.springframework.core.NestedCheckedException;
+import org.springframework.core.NestedExceptionUtils;
 import org.springframework.util.Assert;
 import org.springframework.web.socket.CloseStatus;
 import org.springframework.web.socket.TextMessage;
@@ -70,25 +69,22 @@ private enum State {NEW, OPEN, CLOSED}
 	public static final String DISCONNECTED_CLIENT_LOG_CATEGORY =
 			"org.springframework.web.socket.sockjs.DisconnectedClient";
 
+	/**
+	 * Tomcat: ClientAbortException or EOFException
+	 * Jetty: EofException
+	 * WildFly, GlassFish: java.io.IOException "Broken pipe" (already covered)
+	 * @see #indicatesDisconnectedClient(Throwable)
+	 */
+	private static final Set<String> DISCONNECTED_CLIENT_EXCEPTIONS =
+			new HashSet<String>(Arrays.asList("ClientAbortException", "EOFException", "EofException"));
+
+
 	/**
 	 * Separate logger to use on network IO failure after a client has gone away.
 	 * @see #DISCONNECTED_CLIENT_LOG_CATEGORY
 	 */
 	protected static final Log disconnectedClientLogger = LogFactory.getLog(DISCONNECTED_CLIENT_LOG_CATEGORY);
 
-
-	private static final Set<String> disconnectedClientExceptions;
-
-	static {
-		Set<String> set = new HashSet<String>(4);
-		set.add("ClientAbortException");  // Tomcat
-		set.add("EOFException");  // Tomcat
-		set.add("EofException");  // Jetty
-		// java.io.IOException "Broken pipe" on WildFly, Glassfish (already covered)
-		disconnectedClientExceptions = Collections.unmodifiableSet(set);
-	}
-
-
 	protected final Log logger = LogFactory.getLog(getClass());
 
 	protected final Object responseLock = new Object();
@@ -340,28 +336,28 @@ protected void writeFrame(SockJsFrame frame) throws SockJsTransportFailureExcept
 		}
 	}
 
-	private void logWriteFrameFailure(Throwable failure) {
-		@SuppressWarnings("serial")
-		NestedCheckedException nestedException = new NestedCheckedException("", failure) {};
-
-		if ("Broken pipe".equalsIgnoreCase(nestedException.getMostSpecificCause().getMessage()) ||
-				disconnectedClientExceptions.contains(failure.getClass().getSimpleName())) {
+	protected abstract void writeFrameInternal(SockJsFrame frame) throws IOException;
 
+	private void logWriteFrameFailure(Throwable ex) {
+		if (indicatesDisconnectedClient(ex)) {
 			if (disconnectedClientLogger.isTraceEnabled()) {
-				disconnectedClientLogger.trace("Looks like the client has gone away", failure);
+				disconnectedClientLogger.trace("Looks like the client has gone away", ex);
 			}
 			else if (disconnectedClientLogger.isDebugEnabled()) {
-				disconnectedClientLogger.debug("Looks like the client has gone away: " +
-						nestedException.getMessage() + " (For full stack trace, set the '" +
-						DISCONNECTED_CLIENT_LOG_CATEGORY + "' log category to TRACE level)");
+				disconnectedClientLogger.debug("Looks like the client has gone away: " + ex +
+						" (For a full stack trace, set the log category '" + DISCONNECTED_CLIENT_LOG_CATEGORY +
+						"' to TRACE level.)");
 			}
 		}
 		else {
-			logger.debug("Terminating connection after failure to send message to client", failure);
+			logger.debug("Terminating connection after failure to send message to client", ex);
 		}
 	}
 
-	protected abstract void writeFrameInternal(SockJsFrame frame) throws IOException;
+	private boolean indicatesDisconnectedClient(Throwable ex)  {
+		return ("Broken pipe".equalsIgnoreCase(NestedExceptionUtils.getMostSpecificCause(ex).getMessage()) ||
+				DISCONNECTED_CLIENT_EXCEPTIONS.contains(ex.getClass().getSimpleName()));
+	}
 
 
 	// Delegation methods
@@ -421,7 +417,8 @@ public void tryCloseWithSockJsTransportError(Throwable error, CloseStatus closeS
 			delegateError(error);
 		}
 		catch (Throwable delegateException) {
-			// ignore
+			// Ignore
+			logger.debug("Exception from error handling delegate", delegateException);
 		}
 		try {
 			close(closeStatus);