contextfactory.java

java中比较著名的js引擎当属mozilla开源的rhino

            * we try to protect existing scripts that have specified a
            * version...
            */
            version = cx.getLanguageVersion();
            return (version == Context.VERSION_1_0
                    || version == Context.VERSION_1_1
                    || version == Context.VERSION_1_2);

          case Context.FEATURE_MEMBER_EXPR_AS_FUNCTION_NAME:
            return false;

          case Context.FEATURE_RESERVED_KEYWORD_AS_IDENTIFIER:
            return false;

          case Context.FEATURE_TO_STRING_AS_SOURCE:
            version = cx.getLanguageVersion();
            return version == Context.VERSION_1_2;

          case Context.FEATURE_PARENT_PROTO_PROPRTIES:
            return true;

          case Context.FEATURE_E4X:
            version = cx.getLanguageVersion();
            return (version == Context.VERSION_DEFAULT
                    || version >= Context.VERSION_1_6);

          case Context.FEATURE_DYNAMIC_SCOPE:
            return false;

          case Context.FEATURE_STRICT_VARS:
            return false;

          case Context.FEATURE_STRICT_EVAL:
            return false;
        }
        // It is a bug to call the method with unknown featureIndex
        throw new IllegalArgumentException(String.valueOf(featureIndex));
    }


    /**
     * Create class loader for generated classes.
     * This method creates an instance of the default implementation
     * of {@link GeneratedClassLoader}. Rhino uses this interface to load
     * generated JVM classes when no {@link SecurityController}
     * is installed.
     * Application can override the method to provide custom class loading.
     */
    protected GeneratedClassLoader createClassLoader(ClassLoader parent)
    {
        return new DefiningClassLoader(parent);
    }

    /**
     * Get ClassLoader to use when searching for Java classes.
     * Unless it was explicitly initialized with
     * {@link #initApplicationClassLoader(ClassLoader)} the method returns
     * null to indicate that Thread.getContextClassLoader() should be used.
     */
    public final ClassLoader getApplicationClassLoader()
    {
        return applicationClassLoader;
    }

    /**
     * Set explicit class loader to use when searching for Java classes.
     *
     * @see #getApplicationClassLoader()
     */
    public final void initApplicationClassLoader(ClassLoader loader)
    {
        if (loader == null)
            throw new IllegalArgumentException("loader is null");
        if (!Kit.testIfCanLoadRhinoClasses(loader))
            throw new IllegalArgumentException(
                "Loader can not resolve Rhino classes");

        if (this.applicationClassLoader != null)
            throw new IllegalStateException(
                "applicationClassLoader can only be set once");
        checkNotSealed();

        this.applicationClassLoader = loader;
    }

    /**
     * Execute top call to script or function.
     * When the runtime is about to execute a script or function that will
     * create the first stack frame with scriptable code, it calls this method
     * to perform the real call. In this way execution of any script
     * happens inside this function.
     */
    protected Object doTopCall(Callable callable,
                               Context cx, Scriptable scope,
                               Scriptable thisObj, Object[] args)
    {
        return callable.call(cx, scope, thisObj, args);
    }

    /**
     * Implementation of
     * {@link Context#observeInstructionCount(int instructionCount)}.
     * This can be used to customize {@link Context} without introducing
     * additional subclasses.
     */
    protected void observeInstructionCount(Context cx, int instructionCount)
    {
    }

    protected void onContextCreated(Context cx)
    {
        Object listeners = this.listeners;
        for (int i = 0; ; ++i) {
            Listener l = (Listener)Kit.getListener(listeners, i);
            if (l == null)
                break;
            l.contextCreated(cx);
        }
    }

    protected void onContextReleased(Context cx)
    {
        Object listeners = this.listeners;
        for (int i = 0; ; ++i) {
            Listener l = (Listener)Kit.getListener(listeners, i);
            if (l == null)
                break;
            l.contextReleased(cx);
        }
    }

    public final void addListener(Listener listener)
    {
        checkNotSealed();
        synchronized (listenersLock) {
            if (disabledListening) {
                throw new IllegalStateException();
            }
            listeners = Kit.addListener(listeners, listener);
        }
    }

    public final void removeListener(Listener listener)
    {
        checkNotSealed();
        synchronized (listenersLock) {
            if (disabledListening) {
                throw new IllegalStateException();
            }
            listeners = Kit.removeListener(listeners, listener);
        }
    }

    /**
     * The method is used only to imlement
     * Context.disableStaticContextListening()
     */
    final void disableContextListening()
    {
        checkNotSealed();
        synchronized (listenersLock) {
            disabledListening = true;
            listeners = null;
        }
    }

    /**
     * Checks if this is a sealed ContextFactory.
     * @see #seal()
     */
    public final boolean isSealed()
    {
        return sealed;
    }

    /**
     * Seal this ContextFactory so any attempt to modify it like to add or
     * remove its listeners will throw an exception.
     * @see #isSealed()
     */
    public final void seal()
    {
        checkNotSealed();
        sealed = true;
    }

    protected final void checkNotSealed()
    {
        if (sealed) throw new IllegalStateException();
    }

    /**
     * Call {@link ContextAction#run(Context cx)}
     * using the {@link Context} instance associated with the current thread.
     * If no Context is associated with the thread, then
     * {@link #makeContext()} will be called to construct
     * new Context instance. The instance will be temporary associated
     * with the thread during call to {@link ContextAction#run(Context)}.
     *
     * @see ContextFactory#call(ContextAction)
     * @see Context#call(ContextFactory factory, Callable callable,
     *                   Scriptable scope, Scriptable thisObj,
     *                   Object[] args)
     */
    public final Object call(ContextAction action)
    {
        return Context.call(this, action);
    }
    
    /**
     * Same as {@link Context#enter()} with the difference that if a new context
     * needs to be created, then this context factory is used to create it 
     * instead of the global context factory.
     * @return a Context associated with the current thread
     */
    public final Context enter()
    {
        return enter(null);
    }
    
    /**
     * Same as {@link Context#enter(Context)} with the difference that if a new 
     * context needs to be created, then this context factory is used to create 
     * it instead of the global context factory.
     * @return a Context associated with the current thread
     */
    public final Context enter(Context cx)
    {
        return Context.enter(cx, this);
    }

    /**
     * Same as {@link Context#exit()}, although if you used {@link #enter()} or
     * {@link #enter(Context)} methods on this object, you should use this exit
     * method instead of the static one in {@link Context}. 
     */
    public final void exit()
    {
        Context.exit(this);
    }
}