ReaderException.java

/*
 * Copyright 2007 ZXing authors
 *
 * 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
 * distributed under the License 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.google.zxing;

/**
 * The general exception class throw when something goes wrong during decoding of a barcode.
 * This includes, but is not limited to, failing checksums / error correction algorithms, being
 * unable to locate finder timing patterns, and so on.
 *
 * @author Sean Owen
 */
public abstract class ReaderException extends Exception {

  // TODO: Currently we throw up to 400 ReaderExceptions while scanning a single 240x240 image before
  // rejecting it. This involves a lot of overhead and memory allocation, and affects both performance
  // and latency on continuous scan clients. In the future, we should change all the decoders not to
  // throw exceptions for routine events, like not finding a barcode on a given row. Instead, we
  // should return error codes back to the callers, and simply delete this class. In the mean time, I
  // have altered this class to be as lightweight as possible, by ignoring the exception string, and
  // by disabling the generation of stack traces, which is especially time consuming. These are just
  // temporary measures, pending the big cleanup.

  //private static final ReaderException instance = new ReaderException();

  // EXCEPTION TRACKING SUPPORT
  // Identifies who is throwing exceptions and how often. To use:
  //
  // 1. Uncomment these lines and the code below which uses them.
  // 2. Uncomment the two corresponding lines in j2se/CommandLineRunner.decode()
  // 3. Change core to build as Java 1.5 temporarily
//  private static int exceptionCount = 0;
//  private static Map<String,Integer> throwers = new HashMap<String,Integer>(32);

  ReaderException() {
    // do nothing
  }

  //public static ReaderException getInstance() {
//    Exception e = new Exception();
//    // Take the stack frame before this one.
//    StackTraceElement stack = e.getStackTrace()[1];
//    String key = stack.getClassName() + "." + stack.getMethodName() + "(), line " +
//        stack.getLineNumber();
//    if (throwers.containsKey(key)) {
//      Integer value = throwers.get(key);
//      value++;
//      throwers.put(key, value);
//    } else {
//      throwers.put(key, 1);
//    }
//    exceptionCount++;

    //return instance;
  //}

//  public static int getExceptionCountAndReset() {
//    int temp = exceptionCount;
//    exceptionCount = 0;
//    return temp;
//  }
//
//  public static String getThrowersAndReset() {
//    StringBuilder builder = new StringBuilder(1024);
//    Object[] keys = throwers.keySet().toArray();
//    for (int x = 0; x < keys.length; x++) {
//      String key = (String) keys[x];
//      Integer value = throwers.get(key);
//      builder.append(key);
//      builder.append(": ");
//      builder.append(value);
//      builder.append("\n");
//    }
//    throwers.clear();
//    return builder.toString();
//  }

  // Prevent stack traces from being taken
  // srowen says: huh, my IDE is saying this is not an override. native methods can't be overridden?
  // This, at least, does not hurt. Because we use a singleton pattern here, it doesn't matter anyhow.
  public final Throwable fillInStackTrace() {
    return null;
  }

}