2.1/user/src/com/google/gwt/core/client/JavaScriptException.java

/*
 * Copyright 2008 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.gwt.core.client;

import com.google.gwt.core.client.impl.StackTraceCreator;

/**
 * Any JavaScript exceptions occurring within JSNI methods are wrapped as this
 * class when caught in Java code. The wrapping does not occur until the
 * exception passes out of JSNI into Java. Before that, the thrown object
 * remains a native JavaScript exception object, and can be caught in JSNI as
 * normal.
 * <p>
 * The return value of {@link #getStackTrace()} may vary between browsers due to
 * variations in the underlying error-reporting capabilities. When possible, the
 * stack trace will be the stack trace of the underlying error object. If it is
 * not possible to accurately report a stack trace, a zero-length array will be
 * returned. In those cases where the underlying stack trace cannot be
 * determined, {@link #fillInStackTrace()} can be called in the associated catch
 * block to create a stack trace corresponding to the location where the
 * JavaScriptException object was created.
 * 
 * <pre>
 * try {
 *   nativeMethod();
 * } catch (JavaScriptException e) {
 *   if (e.getStackTrace().length == 0) {
 *     e.fillInStackTrace();
 *   }
 * }
 * </pre>
 */
public final class JavaScriptException extends RuntimeException {

  private static String getDescription(Object e) {
    if (e instanceof JavaScriptObject) {
      return getDescription0((JavaScriptObject) e);
    } else {
      return e + "";
    }
  }

  private static native String getDescription0(JavaScriptObject e) /*-{
    return (e == null) ? null : e.message;
  }-*/;

  private static String getName(Object e) {
    if (e == null) {
      return "null";
    } else if (e instanceof JavaScriptObject) {
      return getName0((JavaScriptObject) e);
    } else if (e instanceof String) {
      return "String";
    } else {
      return e.getClass().getName();
    }
  }

  private static native String getName0(JavaScriptObject e) /*-{
    return (e == null) ? null : e.name;
  }-*/;

  private static String getProperties(Object e) {
    return (e instanceof JavaScriptObject)
        ? getProperties0((JavaScriptObject) e) : "";
  }

  /**
   * Returns the list of properties of an unexpected JavaScript exception.
   */
  private static native String getProperties0(JavaScriptObject e) /*-{
    var result = "";
    try {
      for (var prop in e) {
        if (prop != "name" && prop != "message" && prop != "toString") {
          try {
            result += "\n " + prop + ": " + e[prop];
          } catch (ignored) {
            // Skip the property if it threw an exception.
          }
        }
      }
    } catch (ignored) {
      // If we can't do "in" on the exception, just return what we have.
    }
    return result;
  }-*/;

  /**
   * The original description of the JavaScript exception this class wraps,
   * initialized as <code>e.message</code>.
   */
  private String description;

  /**
   * The underlying exception this class wraps.
   */
  private final Object e;

  /**
   * A constructed message describing this exception.
   */
  private String message;

  /**
   * The original type name of the JavaScript exception this class wraps,
   * initialized as <code>e.name</code>.
   */
  private String name;

  /**
   * @param e the object caught in JavaScript that triggered the exception
   */
  public JavaScriptException(Object e) {
    this.e = e;
    /*
     * In hosted mode, JavaScriptExceptions are created exactly when the native
     * method returns and their stack traces are fixed-up by the hosted-mode
     * plumbing.
     * 
     * In web mode, we'll attempt to infer the stack trace from the thrown
     * object, although this is not possible in all browsers.
     */
    if (GWT.isScript()) {
      StackTraceCreator.createStackTrace(this);
    }
  }

  public JavaScriptException(String name, String description) {
    this.message = "JavaScript " + name + " exception: " + description;
    this.name = name;
    this.description = description;
    this.e = null;
  }

  /**
   * Used for server-side instantiation during JUnit runs. Exceptions are
   * manually marshaled through
   * <code>com.google.gwt.junit.client.impl.ExceptionWrapper</code> objects.
   * 
   * @param message the detail message
   */
  protected JavaScriptException(String message) {
    super(message);
    this.message = this.description = message;
    this.e = null;
  }

  /**
   * Returns the original JavaScript message of the exception; may be
   * <code>null</code>.
   */
  public String getDescription() {
    if (message == null) {
      init();
    }
    return description;
  }

  /**
   * Returns the original JavaScript the exception; may be <code>null</code>.
   */
  public JavaScriptObject getException() {
    return (e instanceof JavaScriptObject) ? (JavaScriptObject) e : null;
  }

  @Override
  public String getMessage() {
    if (message == null) {
      init();
    }
    return message;
  }

  /**
   * Returns the original JavaScript type name of the exception; may be
   * <code>null</code>.
   */
  public String getName() {
    if (message == null) {
      init();
    }
    return name;
  }

  private void init() {
    name = getName(e);
    description = getDescription(e);
    message = "(" + name + "): " + description + getProperties(e);
  }

}