core/src/com/google/inject/internal/Exceptions.java

/**
 * Copyright (C) 2010 Google Inc.
 *
 * 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.inject.internal;

import java.lang.reflect.InvocationTargetException;

/**
 * Rethrows user-code exceptions in wrapped exceptions so that Errors can target the correct
 * exception.
 *
 * @author sameb@google.com (Sam Berlin)
 */
class Exceptions {

  /**
   * Rethrows the exception (or it's cause) directly if possible. If it was a checked exception,
   * this wraps the exception in a stack trace with no frames, so that the exception is shown
   * immediately with no frames above it.
   */
  public static RuntimeException throwCleanly(InvocationTargetException exception) {
    Throwable cause = exception;      
    if(cause.getCause() != null) {
      cause = cause.getCause();
    }
    if(cause instanceof RuntimeException) {
      throw (RuntimeException)cause;
    } else if(cause instanceof Error) {
      throw (Error)cause;
    } else {
      throw new UnhandledCheckedUserException(cause);
    }
  }

  /**
   * A marker exception class that we look for in order to unwrap the exception
   * into the user exception, to provide a cleaner stack trace.
   */
  static class UnhandledCheckedUserException extends RuntimeException {
    public UnhandledCheckedUserException(Throwable cause) {
      super(cause);
    }
  }
}