Java example source code file (SymLinks.java)

This example Java source code file (SymLinks.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.

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Java - Java tags/keywords

basicfileattributes, file, fileoutputstream, files, interruptedexception, ioexception, path, printstream, runtimeexception, string, symlinks, test, unsupportedoperationexception, windows

The SymLinks.java Java example source code

/*
 * Copyright (c) 2009, 2012, 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.
 *
 * 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.
 */

/* @test
 * @bug 6595866
 * @summary Test java.io.File operations with sym links
 * @build SymLinks Util
 * @run main SymLinks
 */

import java.io.*;
import java.nio.file.*;
import java.nio.file.attribute.*;
import static java.nio.file.LinkOption.*;

public class SymLinks {
    final static PrintStream out = System.out;

    final static File top = new File(System.getProperty("test.dir", "."));

    // files used by the test

    final static File file              = new File(top, "foofile");
    final static File link2file         = new File(top, "link2file");
    final static File link2link2file    = new File(top, "link2link2file");

    final static File dir               = new File(top, "foodir");
    final static File link2dir          = new File(top, "link2dir");
    final static File link2link2dir     = new File(top, "link2link2dir");

    final static File link2nobody       = new File(top, "link2nobody");
    final static File link2link2nobody  = new File(top, "link2link2nobody");

    /**
     * Setup files, directories, and sym links used by test.
     */
    static void setup() throws IOException {
        // link2link2file -> link2file -> foofile
        FileOutputStream fos = new FileOutputStream(file);
        try {
            fos.write(new byte[16*1024]);
        } finally {
            fos.close();
        }
        mklink(link2file, file);
        mklink(link2link2file, link2file);

        // link2link2dir -> link2dir -> dir
        assertTrue(dir.mkdir());
        mklink(link2dir, dir);
        mklink(link2link2dir, link2dir);

        // link2link2nobody -> link2nobody -> <does-not-exist>
        mklink(link2nobody, new File(top, "DoesNotExist"));
        mklink(link2link2nobody, link2nobody);
    }

    /**
     * Remove files, directories, and sym links used by test.
     */
    static void cleanup() throws IOException {
        if (file != null)
            file.delete();
        if (link2file != null)
            Files.deleteIfExists(link2file.toPath());
        if (link2link2file != null)
            Files.deleteIfExists(link2link2file.toPath());
        if (dir != null)
            dir.delete();
        if (link2dir != null)
            Files.deleteIfExists(link2dir.toPath());
        if (link2link2dir != null)
            Files.deleteIfExists(link2link2dir.toPath());
        if (link2nobody != null)
            Files.deleteIfExists(link2nobody.toPath());
        if (link2link2nobody != null)
            Files.deleteIfExists(link2link2nobody.toPath());
    }

    /**
     * Creates a sym link source->target
     */
    static void mklink(File source, File target) throws IOException {
        Files.createSymbolicLink(source.toPath(), target.toPath());
    }

    /**
     * Returns true if the "link" exists and is a sym link.
     */
    static boolean isSymLink(File link) {
         return Files.isSymbolicLink(link.toPath());
    }

    /**
     * Returns the last modified time of a sym link.
     */
    static long lastModifiedOfSymLink(File link) throws IOException {
        BasicFileAttributes attrs =
            Files.readAttributes(link.toPath(), BasicFileAttributes.class, NOFOLLOW_LINKS);
        assertTrue(attrs.isSymbolicLink());
        return attrs.lastModifiedTime().toMillis();
    }

    /**
     * Returns true if sym links are supported on the file system where
     * "dir" exists.
     */
    static boolean supportsSymLinks(File dir) {
        Path link = dir.toPath().resolve("link");
        Path target = dir.toPath().resolve("target");
        try {
            Files.createSymbolicLink(link, target);
            Files.delete(link);
            return true;
        } catch (UnsupportedOperationException x) {
            return false;
        } catch (IOException x) {
            return false;
        }
    }

    static void assertTrue(boolean v) {
        if (!v) throw new RuntimeException("Test failed");
    }

    static void assertFalse(boolean v) {
        assertTrue(!v);
    }

    static void header(String h) {
        out.println();
        out.println();
        out.println("-- " + h + " --");
    }

    /**
     * Tests go here.
     */
    static void go() throws IOException {

        // check setup
        assertTrue(file.isFile());
        assertTrue(isSymLink(link2file));
        assertTrue(isSymLink(link2link2file));
        assertTrue(dir.isDirectory());
        assertTrue(isSymLink(link2dir));
        assertTrue(isSymLink(link2link2dir));
        assertTrue(isSymLink(link2nobody));
        assertTrue(isSymLink(link2link2nobody));

        header("createNewFile");

        assertFalse(file.createNewFile());
        assertFalse(link2file.createNewFile());
        assertFalse(link2link2file.createNewFile());
        assertFalse(dir.createNewFile());
        assertFalse(link2dir.createNewFile());
        assertFalse(link2link2dir.createNewFile());
        assertFalse(link2nobody.createNewFile());
        assertFalse(link2link2nobody.createNewFile());

        header("mkdir");

        assertFalse(file.mkdir());
        assertFalse(link2file.mkdir());
        assertFalse(link2link2file.mkdir());
        assertFalse(dir.mkdir());
        assertFalse(link2dir.mkdir());
        assertFalse(link2link2dir.mkdir());
        assertFalse(link2nobody.mkdir());
        assertFalse(link2link2nobody.mkdir());

        header("delete");

        File link = new File(top, "mylink");
        try {
            mklink(link, file);
            assertTrue(link.delete());
            assertTrue(!isSymLink(link));
            assertTrue(file.exists());

            mklink(link, link2file);
            assertTrue(link.delete());
            assertTrue(!isSymLink(link));
            assertTrue(link2file.exists());

            mklink(link, dir);
            assertTrue(link.delete());
            assertTrue(!isSymLink(link));
            assertTrue(dir.exists());

            mklink(link, link2dir);
            assertTrue(link.delete());
            assertTrue(!isSymLink(link));
            assertTrue(link2dir.exists());

            mklink(link, link2nobody);
            assertTrue(link.delete());
            assertTrue(!isSymLink(link));
            assertTrue(isSymLink(link2nobody));

        } finally {
            Files.deleteIfExists(link.toPath());
        }

        header("renameTo");

        File newlink = new File(top, "newlink");
        assertTrue(link2file.renameTo(newlink));
        try {
            assertTrue(file.exists());
            assertTrue(isSymLink(newlink));
            assertTrue(!isSymLink(link2file));
        } finally {
            newlink.renameTo(link2file);  // restore link
        }

        assertTrue(link2dir.renameTo(newlink));
        try {
            assertTrue(dir.exists());
            assertTrue(isSymLink(newlink));
            assertTrue(!isSymLink(link2dir));
        } finally {
            newlink.renameTo(link2dir);  // restore link
        }

        header("list");

        final String name = "entry";
        File entry = new File(dir, name);
        try {
            assertTrue(dir.list().length == 0);   // directory should be empty
            assertTrue(link2dir.list().length == 0);
            assertTrue(link2link2dir.list().length == 0);

            assertTrue(entry.createNewFile());
            assertTrue(dir.list().length == 1);
            assertTrue(dir.list()[0].equals(name));

            // access directory by following links
            assertTrue(link2dir.list().length == 1);
            assertTrue(link2dir.list()[0].equals(name));
            assertTrue(link2link2dir.list().length == 1);
            assertTrue(link2link2dir.list()[0].equals(name));

            // files that are not directories
            assertTrue(link2file.list() == null);
            assertTrue(link2nobody.list() == null);

        } finally {
            entry.delete();
        }

        header("isXXX");

        assertTrue(file.isFile());
        assertTrue(link2file.isFile());
        assertTrue(link2link2file.isFile());

        assertTrue(dir.isDirectory());
        assertTrue(link2dir.isDirectory());
        assertTrue(link2link2dir.isDirectory());

        // on Windows we test with the DOS hidden attribute set
        if (System.getProperty("os.name").startsWith("Windows")) {
            DosFileAttributeView view = Files
                .getFileAttributeView(file.toPath(), DosFileAttributeView.class);
            view.setHidden(true);
            try {
                assertTrue(file.isHidden());
                assertTrue(link2file.isHidden());
                assertTrue(link2link2file.isHidden());
            } finally {
                view.setHidden(false);
            }
            assertFalse(file.isHidden());
            assertFalse(link2file.isHidden());
            assertFalse(link2link2file.isHidden());
        }

        header("length");

        long len = file.length();
        assertTrue(len > 0L);
        // these tests should follow links
        assertTrue(link2file.length() == len);
        assertTrue(link2link2file.length() == len);
        assertTrue(link2nobody.length() == 0L);

        header("lastModified / setLastModified");

        // need time to diff between link and file
        long origLastModified = file.lastModified();
        assertTrue(origLastModified != 0L);
        try { Thread.sleep(2000); } catch (InterruptedException x) { }
        file.setLastModified(System.currentTimeMillis());

        long lastModified = file.lastModified();
        assertTrue(lastModified != origLastModified);
        assertTrue(lastModifiedOfSymLink(link2file) != lastModified);
        assertTrue(lastModifiedOfSymLink(link2link2file) != lastModified);
        assertTrue(link2file.lastModified() == lastModified);
        assertTrue(link2link2file.lastModified() == lastModified);
        assertTrue(link2nobody.lastModified() == 0L);

        origLastModified = dir.lastModified();
        assertTrue(origLastModified != 0L);
        dir.setLastModified(0L);
        assertTrue(dir.lastModified() == 0L);
        assertTrue(link2dir.lastModified() == 0L);
        assertTrue(link2link2dir.lastModified() == 0L);
        dir.setLastModified(origLastModified);

        header("setXXX / canXXX");

        assertTrue(file.canRead());
        assertTrue(file.canWrite());
        assertTrue(link2file.canRead());
        assertTrue(link2file.canWrite());
        assertTrue(link2link2file.canRead());
        assertTrue(link2link2file.canWrite());

        if (!Util.isPrivileged() && file.setReadOnly()) {
            assertFalse(file.canWrite());
            assertFalse(link2file.canWrite());
            assertFalse(link2link2file.canWrite());

            assertTrue(file.setWritable(true));             // make writable
            assertTrue(file.canWrite());
            assertTrue(link2file.canWrite());
            assertTrue(link2link2file.canWrite());

            assertTrue(link2file.setReadOnly());            // make read only
            assertFalse(file.canWrite());
            assertFalse(link2file.canWrite());
            assertFalse(link2link2file.canWrite());

            assertTrue(link2link2file.setWritable(true));   // make writable
            assertTrue(file.canWrite());
            assertTrue(link2file.canWrite());
            assertTrue(link2link2file.canWrite());
        }
    }

    public static void main(String[] args) throws IOException {
        if (supportsSymLinks(top)) {
            try {
                setup();
                go();
            } finally {
                cleanup();
            }
        }
    }

}