Java example source code file (Bridge.java)

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Java - Java tags/keywords

bridge, class, classloader, constructor, could, error, field, invalid_field_offset, method, no_args, object, privilegedaction, reflection, security, throwable, unsafe

The Bridge.java Java example source code

/*
 * Copyright (c) 2004, 2010, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package sun.corba ;

import java.lang.reflect.Field ;
import java.lang.reflect.Method ;
import java.lang.reflect.Constructor ;
import java.lang.reflect.InvocationTargetException ;

import java.io.ObjectInputStream ;

import java.security.AccessController;
import java.security.Permission;
import java.security.PrivilegedAction;

import sun.misc.Unsafe ;
import sun.reflect.ReflectionFactory ;

/** This class provides the methods for fundamental JVM operations
 * needed in the ORB that are not part of the public Java API.  This includes:
 * <ul>
 * <li>throwException, which can throw undeclared checked exceptions.
 * This is needed to handle throwing arbitrary exceptions across a standardized OMG interface that (incorrectly) does not specify appropriate exceptions.</li>
 * <li>putXXX/getXXX methods that allow unchecked access to fields of objects.
 * This is used for setting uninitialzed non-static final fields (which is
 * impossible with reflection) and for speed.</li>
 * <li>objectFieldOffset to obtain the field offsets for use in the putXXX/getXXX methods
 * <li>newConstructorForSerialization to get the special constructor required for a
 * Serializable class</li>
 * <li>latestUserDefinedLoader to get the latest user defined class loader from
 * the call stack as required by the RMI-IIOP specification (really from the
 * JDK 1.1 days)</li>
 * </ul>
 * The code that calls Bridge.get() must have the following Permissions:
 * <ul>
 * <li>RuntimePermission "reflectionFactoryAccess"
 * <li>BridgePermission "getBridge"
 * <li>ReflectPermission "suppressAccessChecks"
 * </ul>
 * <p>
 * All of these permissions are required to obtain and correctly initialize
 * the instance of Bridge.  No security checks are performed on calls
 * made to Bridge instance methods, so access to the Bridge instance
 * must be protected.
 * <p>
 * This class is a singleton (per ClassLoader of course).  Access to the
 * instance is obtained through the Bridge.get() method.
 */
public final class Bridge
{
    private static final Class[] NO_ARGS = new Class[] {};
    private static final Permission getBridgePermission =
        new BridgePermission( "getBridge" ) ;
    private static Bridge bridge = null ;

    // latestUserDefinedLoader() is a private static method
    // in ObjectInputStream in JDK 1.3 through 1.5.
    // We use reflection in a doPrivileged block to get a
    // Method reference and make it accessible.
    private final Method latestUserDefinedLoaderMethod ;
    private final Unsafe unsafe ;
    private final ReflectionFactory reflectionFactory ;

    private Method getLatestUserDefinedLoaderMethod()
    {
        return (Method) AccessController.doPrivileged(
            new PrivilegedAction()
            {
                public Object run()
                {
                    Method result = null;

                    try {
                        Class io = ObjectInputStream.class;
                        result = io.getDeclaredMethod(
                            "latestUserDefinedLoader", NO_ARGS);
                        result.setAccessible(true);
                    } catch (NoSuchMethodException nsme) {
                        Error err = new Error( "java.io.ObjectInputStream" +
                            " latestUserDefinedLoader " + nsme );
                        err.initCause(nsme) ;
                        throw err ;
                    }

                    return result;
                }
            }
        );
    }

    private Unsafe getUnsafe() {
        Field fld = (Field)AccessController.doPrivileged(
            new PrivilegedAction()
            {
                public Object run()
                {
                    Field fld = null ;

                    try {
                        Class unsafeClass = sun.misc.Unsafe.class ;
                        fld = unsafeClass.getDeclaredField( "theUnsafe" ) ;
                        fld.setAccessible( true ) ;
                        return fld ;
                    } catch (NoSuchFieldException exc) {
                        Error err = new Error( "Could not access Unsafe" ) ;
                        err.initCause( exc ) ;
                        throw err ;
                    }
                }
            }
        ) ;

        Unsafe unsafe = null;

        try {
            unsafe = (Unsafe)(fld.get( null )) ;
        } catch (Throwable t) {
            Error err = new Error( "Could not access Unsafe" ) ;
            err.initCause( t ) ;
            throw err ;
        }

        return unsafe ;
    }


    private Bridge()
    {
        latestUserDefinedLoaderMethod = getLatestUserDefinedLoaderMethod();
        unsafe = getUnsafe() ;
        reflectionFactory = (ReflectionFactory)AccessController.doPrivileged(
            new ReflectionFactory.GetReflectionFactoryAction());
    }

    /** Fetch the Bridge singleton.  This requires the following
     * permissions:
     * <ul>
     * <li>RuntimePermission "reflectionFactoryAccess"
     * <li>BridgePermission "getBridge"
     * <li>ReflectPermission "suppressAccessChecks"
     * </ul>
     * @return The singleton instance of the Bridge class
     * @throws SecurityException if the caller does not have the
     * required permissions and the caller has a non-null security manager.
     */
    public static final synchronized Bridge get()
    {
        SecurityManager sman = System.getSecurityManager() ;
        if (sman != null)
            sman.checkPermission( getBridgePermission ) ;

        if (bridge == null) {
            bridge = new Bridge() ;
        }

        return bridge ;
    }

    /** Obtain the latest user defined ClassLoader from the call stack.
     * This is required by the RMI-IIOP specification.
     */
    public final ClassLoader getLatestUserDefinedLoader()
    {
        try {
            // Invoke the ObjectInputStream.latestUserDefinedLoader method
            return (ClassLoader)latestUserDefinedLoaderMethod.invoke(null,
                                                                     (Object[])NO_ARGS);
        } catch (InvocationTargetException ite) {
            Error err = new Error(
                "sun.corba.Bridge.latestUserDefinedLoader: " + ite ) ;
            err.initCause( ite ) ;
            throw err ;
        } catch (IllegalAccessException iae) {
            Error err = new Error(
                "sun.corba.Bridge.latestUserDefinedLoader: " + iae ) ;
            err.initCause( iae ) ;
            throw err ;
        }
    }

    /**
     * Fetches a field element within the given
     * object <code>o at the given offset.
     * The result is undefined unless the offset was obtained from
     * {@link #objectFieldOffset} on the {@link java.lang.reflect.Field}
     * of some Java field and the object referred to by <code>o
     * is of a class compatible with that field's class.
     * @param o Java heap object in which the field from which the offset
     * was obtained resides
     * @param offset indication of where the field resides in a Java heap
     *        object
     * @return the value fetched from the indicated Java field
     * @throws RuntimeException No defined exceptions are thrown, not even
     *         {@link NullPointerException}
     */
    public final int getInt(Object o, long offset)
    {
        return unsafe.getInt( o, offset ) ;
    }

    /**
     * Stores a value into a given Java field.
     * <p>
     * The first two parameters are interpreted exactly as with
     * {@link #getInt(Object, long)} to refer to a specific
     * Java field.  The given value is stored into that field.
     * <p>
     * The field must be of the same type as the method
     * parameter <code>x.
     *
     * @param o Java heap object in which the field resides, if any, else
     *        null
     * @param offset indication of where the field resides in a Java heap
     *        object.
     * @param x the value to store into the indicated Java field
     * @throws RuntimeException No defined exceptions are thrown, not even
     *         {@link NullPointerException}
     */
    public final void putInt(Object o, long offset, int x)
    {
        unsafe.putInt( o, offset, x ) ;
    }

    /**
     * @see #getInt(Object, long)
     */
    public final Object getObject(Object o, long offset)
    {
        return unsafe.getObject( o, offset ) ;
    }

    /**
     * @see #putInt(Object, long, int)
     */
    public final void putObject(Object o, long offset, Object x)
    {
        unsafe.putObject( o, offset, x ) ;
    }

    /** @see #getInt(Object, long) */
    public final boolean getBoolean(Object o, long offset)
    {
        return unsafe.getBoolean( o, offset ) ;
    }
    /** @see #putInt(Object, long, int) */
    public final void    putBoolean(Object o, long offset, boolean x)
    {
        unsafe.putBoolean( o, offset, x ) ;
    }
    /** @see #getInt(Object, long) */
    public final byte    getByte(Object o, long offset)
    {
        return unsafe.getByte( o, offset ) ;
    }
    /** @see #putInt(Object, long, int) */
    public final void    putByte(Object o, long offset, byte x)
    {
        unsafe.putByte( o, offset, x ) ;
    }
    /** @see #getInt(Object, long) */
    public final short   getShort(Object o, long offset)
    {
        return unsafe.getShort( o, offset ) ;
    }
    /** @see #putInt(Object, long, int) */
    public final void    putShort(Object o, long offset, short x)
    {
        unsafe.putShort( o, offset, x ) ;
    }
    /** @see #getInt(Object, long) */
    public final char    getChar(Object o, long offset)
    {
        return unsafe.getChar( o, offset ) ;
    }
    /** @see #putInt(Object, long, int) */
    public final void    putChar(Object o, long offset, char x)
    {
        unsafe.putChar( o, offset, x ) ;
    }
    /** @see #getInt(Object, long) */
    public final long    getLong(Object o, long offset)
    {
        return unsafe.getLong( o, offset ) ;
    }
    /** @see #putInt(Object, long, int) */
    public final void    putLong(Object o, long offset, long x)
    {
        unsafe.putLong( o, offset, x ) ;
    }
    /** @see #getInt(Object, long) */
    public final float   getFloat(Object o, long offset)
    {
        return unsafe.getFloat( o, offset ) ;
    }
    /** @see #putInt(Object, long, int) */
    public final void    putFloat(Object o, long offset, float x)
    {
        unsafe.putFloat( o, offset, x ) ;
    }
    /** @see #getInt(Object, long) */
    public final double  getDouble(Object o, long offset)
    {
        return unsafe.getDouble( o, offset ) ;
    }
    /** @see #putInt(Object, long, int) */
    public final void    putDouble(Object o, long offset, double x)
    {
        unsafe.putDouble( o, offset, x ) ;
    }

    /**
     * This constant differs from all results that will ever be returned from
     * {@link #objectFieldOffset}.
     */
    public static final long INVALID_FIELD_OFFSET   = -1;

    /**
     * Returns the offset of a non-static field.
     */
    public final long objectFieldOffset(Field f)
    {
        return unsafe.objectFieldOffset( f ) ;
    }

    /** Throw the exception.
     * The exception may be an undeclared checked exception.
     */
    public final void throwException(Throwable ee)
    {
        unsafe.throwException( ee ) ;
    }

    /** Obtain a constructor for Class cl using constructor cons which
     * may be the constructor defined in a superclass of cl.  This is
     * used to create a constructor for Serializable classes that
     * constructs an instance of the Serializable class using the
     * no args constructor of the first non-Serializable superclass
     * of the Serializable class.
     */
    public final Constructor newConstructorForSerialization( Class cl,
        Constructor cons )
    {
        return reflectionFactory.newConstructorForSerialization( cl, cons ) ;
    }
}