Java example source code file (UnixChannelFactory.java)

This example Java source code file (UnixChannelFactory.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

append, delete_on_close, filechannel, filedescriptor, flags, illegalargumentexception, o_nofollow, openoption, read, set, string, unixexception, unixpath, unsupportedoperationexception, util

The UnixChannelFactory.java Java example source code

/*
 * Copyright (c) 2008, 2013, 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.nio.fs;

import java.nio.file.*;
import java.nio.channels.*;
import java.io.FileDescriptor;
import java.util.Set;

import sun.nio.ch.FileChannelImpl;
import sun.nio.ch.ThreadPool;
import sun.nio.ch.SimpleAsynchronousFileChannelImpl;
import sun.misc.SharedSecrets;
import sun.misc.JavaIOFileDescriptorAccess;

import static sun.nio.fs.UnixNativeDispatcher.*;
import static sun.nio.fs.UnixConstants.*;

/**
 * Factory for FileChannels and AsynchronousFileChannels
 */

class UnixChannelFactory {
    private static final JavaIOFileDescriptorAccess fdAccess =
        SharedSecrets.getJavaIOFileDescriptorAccess();

    protected UnixChannelFactory() {
    }

    /**
     * Represents the flags from a user-supplied set of open options.
     */
    protected static class Flags {
        boolean read;
        boolean write;
        boolean append;
        boolean truncateExisting;
        boolean noFollowLinks;
        boolean create;
        boolean createNew;
        boolean deleteOnClose;
        boolean sync;
        boolean dsync;

        static Flags toFlags(Set<? extends OpenOption> options) {
            Flags flags = new Flags();
            for (OpenOption option: options) {
                if (option instanceof StandardOpenOption) {
                    switch ((StandardOpenOption)option) {
                        case READ : flags.read = true; break;
                        case WRITE : flags.write = true; break;
                        case APPEND : flags.append = true; break;
                        case TRUNCATE_EXISTING : flags.truncateExisting = true; break;
                        case CREATE : flags.create = true; break;
                        case CREATE_NEW : flags.createNew = true; break;
                        case DELETE_ON_CLOSE : flags.deleteOnClose = true; break;
                        case SPARSE : /* ignore */ break;
                        case SYNC : flags.sync = true; break;
                        case DSYNC : flags.dsync = true; break;
                        default: throw new UnsupportedOperationException();
                    }
                    continue;
                }
                if (option == LinkOption.NOFOLLOW_LINKS && O_NOFOLLOW != 0) {
                    flags.noFollowLinks = true;
                    continue;
                }
                if (option == null)
                    throw new NullPointerException();
               throw new UnsupportedOperationException(option + " not supported");
            }
            return flags;
        }
    }


    /**
     * Constructs a file channel from an existing (open) file descriptor
     */
    static FileChannel newFileChannel(int fd, boolean reading, boolean writing) {
        FileDescriptor fdObj = new FileDescriptor();
        fdAccess.set(fdObj, fd);
        return FileChannelImpl.open(fdObj, reading, writing, null);
    }

    /**
     * Constructs a file channel by opening a file using a dfd/path pair
     */
    static FileChannel newFileChannel(int dfd,
                                      UnixPath path,
                                      String pathForPermissionCheck,
                                      Set<? extends OpenOption> options,
                                      int mode)
        throws UnixException
    {
        Flags flags = Flags.toFlags(options);

        // default is reading; append => writing
        if (!flags.read && !flags.write) {
            if (flags.append) {
                flags.write = true;
            } else {
                flags.read = true;
            }
        }

        // validation
        if (flags.read && flags.append)
            throw new IllegalArgumentException("READ + APPEND not allowed");
        if (flags.append && flags.truncateExisting)
            throw new IllegalArgumentException("APPEND + TRUNCATE_EXISTING not allowed");

        FileDescriptor fdObj = open(dfd, path, pathForPermissionCheck, flags, mode);
        return FileChannelImpl.open(fdObj, flags.read, flags.write, flags.append, null);
    }

    /**
     * Constructs a file channel by opening the given file.
     */
    static FileChannel newFileChannel(UnixPath path,
                                      Set<? extends OpenOption> options,
                                      int mode)
        throws UnixException
    {
        return newFileChannel(-1, path, null, options, mode);
    }

    /**
     * Constructs an asynchronous file channel by opening the given file.
     */
    static AsynchronousFileChannel newAsynchronousFileChannel(UnixPath path,
                                                              Set<? extends OpenOption> options,
                                                              int mode,
                                                              ThreadPool pool)
        throws UnixException
    {
        Flags flags = Flags.toFlags(options);

        // default is reading
        if (!flags.read && !flags.write) {
            flags.read = true;
        }

        // validation
        if (flags.append)
            throw new UnsupportedOperationException("APPEND not allowed");

        // for now use simple implementation
        FileDescriptor fdObj = open(-1, path, null, flags, mode);
        return SimpleAsynchronousFileChannelImpl.open(fdObj, flags.read, flags.write, pool);
    }

    /**
     * Opens file based on parameters and options, returning a FileDescriptor
     * encapsulating the handle to the open file.
     */
    protected static FileDescriptor open(int dfd,
                                         UnixPath path,
                                         String pathForPermissionCheck,
                                         Flags flags,
                                         int mode)
        throws UnixException
    {
        // map to oflags
        int oflags;
        if (flags.read && flags.write) {
            oflags = O_RDWR;
        } else {
            oflags = (flags.write) ? O_WRONLY : O_RDONLY;
        }
        if (flags.write) {
            if (flags.truncateExisting)
                oflags |= O_TRUNC;
            if (flags.append)
                oflags |= O_APPEND;

            // create flags
            if (flags.createNew) {
                byte[] pathForSysCall = path.asByteArray();

                // throw exception if file name is "." to avoid confusing error
                if ((pathForSysCall[pathForSysCall.length-1] == '.') &&
                    (pathForSysCall.length == 1 ||
                    (pathForSysCall[pathForSysCall.length-2] == '/')))
                {
                    throw new UnixException(EEXIST);
                }
                oflags |= (O_CREAT | O_EXCL);
            } else {
                if (flags.create)
                    oflags |= O_CREAT;
            }
        }

        // follow links by default
        boolean followLinks = true;
        if (!flags.createNew && (flags.noFollowLinks || flags.deleteOnClose)) {
            if (flags.deleteOnClose && O_NOFOLLOW == 0) {
                try {
                    if (UnixFileAttributes.get(path, false).isSymbolicLink())
                        throw new UnixException("DELETE_ON_CLOSE specified and file is a symbolic link");
                } catch (UnixException x) {
                    if (!flags.create || x.errno() != ENOENT)
                        throw x;
                }
            }
            followLinks = false;
            oflags |= O_NOFOLLOW;
        }

        if (flags.dsync)
            oflags |= O_DSYNC;
        if (flags.sync)
            oflags |= O_SYNC;

        // permission check before we open the file
        SecurityManager sm = System.getSecurityManager();
        if (sm != null) {
            if (pathForPermissionCheck == null)
                pathForPermissionCheck = path.getPathForPermissionCheck();
            if (flags.read)
                sm.checkRead(pathForPermissionCheck);
            if (flags.write)
                sm.checkWrite(pathForPermissionCheck);
            if (flags.deleteOnClose)
                sm.checkDelete(pathForPermissionCheck);
        }

        int fd;
        try {
            if (dfd >= 0) {
                fd = openat(dfd, path.asByteArray(), oflags, mode);
            } else {
                fd = UnixNativeDispatcher.open(path, oflags, mode);
            }
        } catch (UnixException x) {
            // Linux error can be EISDIR or EEXIST when file exists
            if (flags.createNew && (x.errno() == EISDIR)) {
                x.setError(EEXIST);
            }

            // handle ELOOP to avoid confusing message
            if (!followLinks && (x.errno() == ELOOP)) {
                x = new UnixException(x.getMessage() + " (NOFOLLOW_LINKS specified)");
            }

            throw x;
        }

        // unlink file immediately if delete on close. The spec is clear that
        // an implementation cannot guarantee to unlink the correct file when
        // replaced by an attacker after it is opened.
        if (flags.deleteOnClose) {
            try {
                if (dfd >= 0) {
                    unlinkat(dfd, path.asByteArray(), 0);
                } else {
                    unlink(path);
                }
            } catch (UnixException ignore) {
                // best-effort
            }
        }

        // create java.io.FileDescriptor
        FileDescriptor fdObj = new FileDescriptor();
        fdAccess.set(fdObj, fd);
        return fdObj;
    }
}