DebugObjectOutputStream.java

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 * obtain a copy of the License at
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 * This file incorporates work covered by the following copyright and
 * permission notice:
 *
 * Copyright 2005-2007 The Apache Software Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
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package com.sun.faces.util;


import java.io.ObjectOutputStream;
import java.io.OutputStream;
import java.io.IOException;
import java.lang.reflect.Field;
import java.util.List;
import java.util.ArrayList;

/*
 * From: http://blog.crazybob.org/2007/02/debugging-serialization.html
 * 
 * Usage example:

                DebugObjectOutputStream out =
                        new DebugObjectOutputStream(oos);
                try {
                    out.writeObject(stateToWrite[1]);
                } catch (Exception e) {
                    DebugUtil.printState((Map)stateToWrite[1], LOGGER);
                    throw new FacesException(
                            "Serialization error. Path to offending instance: " 
                            + out.getStack(), e);
                }            

 
 
 * 
 * 
 */

public class DebugObjectOutputStream
    extends ObjectOutputStream {

  private static final Field DEPTH_FIELD;
  static {
    try {
      DEPTH_FIELD = ObjectOutputStream.class
          .getDeclaredField("depth");
      DEPTH_FIELD.setAccessible(true);
    } catch (NoSuchFieldException e) {
      throw new AssertionError(e);
    }
  }

  final List<Object> stack
      = new ArrayList<>();

  /**
   * Indicates whether or not OOS has tried to
   * write an IOException (presumably as the
   * result of a serialization error) to the
   * stream.
   */
  boolean broken = false;

  public DebugObjectOutputStream(
      OutputStream out) throws IOException {
    super(out);
    enableReplaceObject(true);
  }

  /**
   * Abuse {@code replaceObject()} as a hook to
   * maintain our stack.
   */
  @Override
  protected Object replaceObject(Object o) {
    // ObjectOutputStream writes serialization
    // exceptions to the stream. Ignore
    // everything after that so we don't lose
    // the path to a non-serializable object. So
    // long as the user doesn't write an
    // IOException as the root object, we're OK.
    int currentDepth = currentDepth();
    if (o instanceof IOException
        && currentDepth == 0) {
      broken = true;
    }
    if (!broken) {
      truncate(currentDepth);
      stack.add(o);
    }
    return o;
  }

  private void truncate(int depth) {
    while (stack.size() > depth) {
      pop();
    }
  }

  private Object pop() {
    return stack.remove(stack.size() - 1);
  }

  /**
   * Returns a 0-based depth within the object
   * graph of the current object being
   * serialized.
   */
  private int currentDepth() {
    try {
      Integer oneBased
          = ((Integer) DEPTH_FIELD.get(this));
      return oneBased - 1;
    } catch (IllegalAccessException e) {
      throw new AssertionError(e);
    }
  }

  /**
   * Returns the path to the last object
   * serialized. If an exception occurred, this
   * should be the path to the non-serializable
   * object.
   */
  public List<Object> getStack() {
    return stack;
  }
}