/*
* 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.Impl;
/**
* Supports core functionality that in some cases requires direct support from
* the compiler and runtime systems such as runtime type information and
* deferred binding.
*/
public final class GWT {
/**
* This interface is used to catch exceptions at the "top level" just before
* they escape to the browser. This is used in places where the browser calls
* into user code such as event callbacks, timers, and RPC.
*
* In Development Mode, the default handler prints a stack trace to the log
* window. In Production Mode, the default handler is null and thus exceptions
* are allowed to escape, which provides an opportunity to use a JavaScript
* debugger.
*/
public interface UncaughtExceptionHandler {
void onUncaughtException(Throwable e);
}
/**
* An {@link UncaughtExceptionHandler} that logs errors to
* {@link GWT#log(String, Throwable)}. This is the default exception handler
* in Development Mode. In Production Mode, the default exception handler is
* <code>null</code>.
*/
private static final class DefaultUncaughtExceptionHandler implements
UncaughtExceptionHandler {
public void onUncaughtException(Throwable e) {
log("Uncaught exception escaped", e);
}
}
/**
* This constant is used by {@link #getPermutationStrongName} when running in
* Development Mode.
*/
public static final String HOSTED_MODE_PERMUTATION_STRONG_NAME = "HostedMode";
/**
* Always <code>null</code> in Production Mode; in Development Mode provides
* the implementation for certain methods.
*/
private static GWTBridge sGWTBridge = null;
/**
* Defaults to <code>null</code> in Production Mode and an instance of
* {@link DefaultUncaughtExceptionHandler} in Development Mode.
*/
private static UncaughtExceptionHandler sUncaughtExceptionHandler = null;
/**
* Instantiates a class via deferred binding.
*
* <p>
* The argument to {@link #create(Class)} <i>must</i> be a class literal
* because the Production Mode compiler must be able to statically determine
* the requested type at compile-time. This can be tricky because using a
* {@link Class} variable may appear to work correctly in Development Mode.
* </p>
*
* @param classLiteral a class literal specifying the base class to be
* instantiated
* @return the new instance, which must be typecast to the requested class.
*/
public static <T> T create(Class<?> classLiteral) {
if (sGWTBridge == null) {
/*
* In Production Mode, the compiler directly replaces calls to this method
* with a new Object() type expression of the correct rebound type.
*/
throw new UnsupportedOperationException(
"ERROR: GWT.create() is only usable in client code! It cannot be called, "
+ "for example, from server code. If you are running a unit test, "
+ "check that your test case extends GWTTestCase and that GWT.create() "
+ "is not called from within an initializer or constructor.");
} else {
return sGWTBridge.<T> create(classLiteral);
}
}
/**
* Gets the URL prefix of the hosting page, useful for prepending to relative
* paths of resources which may be relative to the host page. Typically, you
* should use {@link #getModuleBaseURL()} unless you have a specific reason to
* load a resource relative to the host page.
*
* @return if non-empty, the base URL is guaranteed to end with a slash
*/
public static String getHostPageBaseURL() {
return Impl.getHostPageBaseURL();
}
/**
* Gets the URL prefix of the module which should be prepended to URLs that
* are intended to be module-relative, such as RPC entry points and files in
* the module's public path.
*
* @return if non-empty, the base URL is guaranteed to end with a slash
*/
public static String getModuleBaseURL() {
return Impl.getModuleBaseURL();
}
/**
* Gets the name of the running module.
*/
public static String getModuleName() {
return Impl.getModuleName();
}
/**
* Returns the permutation's strong name. This can be used to distinguish
* between different permutations of the same module. In Development Mode,
* this method will return {@value #HOSTED_MODE_PERMUTATION_STRONG_NAME}.
*/
public static String getPermutationStrongName() {
if (GWT.isScript()) {
return Impl.getPermutationStrongName();
} else {
return HOSTED_MODE_PERMUTATION_STRONG_NAME;
}
}
/**
* @deprecated Use {@link Object#getClass()}, {@link Class#getName()}
*/
@Deprecated
public static String getTypeName(Object o) {
return (o == null) ? null : o.getClass().getName();
}
/**
* Returns the currently active uncaughtExceptionHandler. "Top level" methods
* that dispatch events from the browser into user code must call this method
* on entry to get the active handler. If the active handler is null, the
* entry point must allow exceptions to escape into the browser. If the
* handler is non-null, exceptions must be caught and routed to the handler.
* See the source code for <code>DOM.dispatchEvent()</code> for an example
* of how to handle this correctly.
*
* @return the currently active handler, or null if no handler is active.
*/
public static UncaughtExceptionHandler getUncaughtExceptionHandler() {
return sUncaughtExceptionHandler;
}
/**
* Returns the empty string when running in Production Mode, but returns a
* unique string for each thread in Development Mode (for example, different
* windows accessing the dev mode server will each have a unique id, and
* hitting refresh without restarting dev mode will result in a new unique id
* for a particular window.
*
* TODO(unnurg): Remove this function once Dev Mode rewriting classes are in
* gwt-dev.
*/
public static String getUniqueThreadId() {
if (sGWTBridge != null) {
return sGWTBridge.getThreadUniqueID();
}
return "";
}
public static String getVersion() {
if (sGWTBridge == null) {
return getVersion0();
} else {
return sGWTBridge.getVersion();
}
}
/**
* Returns <code>true</code> when running inside the normal GWT environment,
* either in Development Mode or Production Mode. Returns <code>false</code>
* if this code is running in a plain JVM. This might happen when running
* shared code on the server, or during the bootstrap sequence of a
* GWTTestCase test.
*/
public static boolean isClient() {
// Replaced with "true" by GWT compiler.
return sGWTBridge != null && sGWTBridge.isClient();
}
/**
* Returns <code>true</code> when running in production mode. Returns
* <code>false</code> when running either in development mode, or when running
* in a plain JVM.
*/
public static boolean isProdMode() {
// Replaced with "true" by GWT compiler.
return false;
}
/**
* Determines whether or not the running program is script or bytecode.
*/
public static boolean isScript() {
// Replaced with "true" by GWT compiler.
return false;
}
/**
* Logs a message to the development shell logger in Development Mode. Calls
* are optimized out in Production Mode.
*/
public static void log(String message) {
log(message, null);
}
/**
* Logs a message to the development shell logger in Development Mode. Calls
* are optimized out in Production Mode.
*/
public static void log(String message, Throwable e) {
if (sGWTBridge != null) {
sGWTBridge.log(message, e);
}
}
/**
* The same as {@link #runAsync(RunAsyncCallback)}, except with an extra
* parameter to provide a name for the call. The name parameter should be
* supplied with a class literal. No two runAsync calls in the same program
* should use the same name.
*/
@SuppressWarnings("unused") // parameter will be used following replacement
public static void runAsync(Class<?> name, RunAsyncCallback callback) {
callback.onSuccess();
}
/**
* Run the specified callback once the necessary code for it has been loaded.
*/
public static void runAsync(RunAsyncCallback callback) {
callback.onSuccess();
}
/**
* Sets a custom uncaught exception handler. See
* {@link #getUncaughtExceptionHandler()} for details.
*
* @param handler the handler that should be called when an exception is about
* to escape to the browser, or <code>null</code> to clear the
* handler and allow exceptions to escape.
*/
public static void setUncaughtExceptionHandler(
UncaughtExceptionHandler handler) {
sUncaughtExceptionHandler = handler;
}
/**
* Called via reflection in Development Mode; do not ever call this method in
* Production Mode.
*/
static void setBridge(GWTBridge bridge) {
sGWTBridge = bridge;
if (bridge != null) {
setUncaughtExceptionHandler(new DefaultUncaughtExceptionHandler());
}
}
private static native String getVersion0() /*-{
return $gwt_version;
}-*/;
}