content: /*
   * Copyright 2007-2019 Amazon.com, Inc. or its affiliates. All Rights Reserved.
   *
   * Licensed under the Apache License, Version 2.0 (the "License").
   * You may not use this file except in compliance with the License.
   * A copy of the License is located at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * or in the "license" file accompanying this file. This file is distributed
   * on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
   * express or implied. See the License for the specific language governing
   * permissions and limitations under the License.
   */
  
  package com.amazon.ion;
  
  import java.io.IOException;
  import java.util.IdentityHashMap;
  
  /**
   * Base class for exceptions thrown throughout this library.  In most cases,
   * external exceptions (a common example being {@link IOException}) are not
   * propagated directly but are instead wrapped in one or more
   * {@link IonException}s.
   * <p>
   * This library does not promise that such an "external cause" will be the
   * direct {@link IonException#getCause() cause} of the thrown exception: there
   * there may be a chain of multiple {@link IonException} before getting to the
   * external cause.  Here's an example of how to deal with this in a situation
   * where the caller wants to propagate {@link IOException}s:
   *<pre>
   *    try {
   *        // Call some API
   *    }
   *    catch (IonException e) {
   *        IOException io = e.causeOfType(IOException.class);
   *        if (io != null) throw io;
   *        throw e;
   *    }
   *</pre>
   */
  public class IonException extends RuntimeException
  {
      private static final long serialVersionUID = 5769577011706279252L;
  
      public IonException() { super(); }
      public IonException(String message) { super(message); }
      public IonException(String message, Throwable cause) {
          super(message, cause);
      }
  
      /**
       * Constructs a new exception with the given cause, copying the message
       * from the cause into this instance.
       * @param cause
       *     the root cause of the exception; must not be null.
       */
      public IonException(Throwable cause) { super(cause.getMessage(), cause); }
  
  
      /**
       * Finds the first exception in the {@link #getCause()} chain that's not
       * an {@link IonException}.
       *
       * @return null if there's no cause that's not an {@link IonException}.
       */
      Throwable externalCause()
      {
          IdentityHashMap<Throwable, Throwable> seen =
              new IdentityHashMap<Throwable, Throwable>();
  
          Throwable cause = getCause();
          while (cause instanceof IonException)
          {
              if (seen.put(cause, cause) != null)  // cycle check
              {
                  return null;
              }
              cause = cause.getCause();
          }
          return cause;
      }
  
  
      /**
       * Finds the first exception in the {@link #getCause()} chain that is
       * an instance of the given type.
       *
       * @return null if there's no cause of the given type.
       */
      @SuppressWarnings("unchecked")
      public <T extends Throwable> T causeOfType(Class<T> type)
      {
          IdentityHashMap<Throwable, Throwable> seen =
              new IdentityHashMap<Throwable, Throwable>();
  
          Throwable cause = getCause();
          while (cause != null && ! type.isInstance(cause))
          {
              if (seen.put(cause, cause) != null)  // cycle check
              {
                  return null;
              }
              cause = cause.getCause();
          }
          return (T) cause;
      }
  
      /**
       * Rethrows the first exception in the {@link #getCause()} chain that is
       * an instance of the given type.  If no such cause is found, returns
       * normally.
       *
       * FIXME Doesn't work under Java 5
       */
      @SuppressWarnings("unused")
      private // until I can get this to work
      <T extends Throwable> void rethrowCauseOfType(Class<T> type)
          throws Throwable // this should be throws T
      {
          T cause = causeOfType(type);
  
          // rethrow acts as if its always throwing Throwable, not the subclass.
          if (cause != null) throw cause;
      }
  }
  