Zarkonnen Zarkonnen - 3 months ago 15
Java Question

Windows shortcut (.lnk) parser in Java?

I'm currently using

Win32ShellFolderManager2
and
ShellFolder.getLinkLocation
to resolve windows shortcuts in Java. Unfortunately, if the Java program is running as a service under Vista,
getLinkLocation
, this does not work. Specifically, I get an exception stating "Could not get shell folder ID list".

Searching the web does turn up mentions of this error message, but always in connection with
JFileChooser
. I'm not using
JFileChooser
, I just need to resolve a
.lnk
file to its destination.

Does anyone know of a 3rd-party parser for
.lnk
files written in Java I could use?

I've since found unofficial documentation for the .lnk format here, but I'd rather not have to do the work if anyone has done it before, since the format is rather scary.

Answer

Added comments (some explanation as well as credit to each contributor so far),additional check on the file magic, a quick test to see if a given file might be a valid link (without reading all of the bytes), a fix to throw a ParseException with appropriate message instead of ArrayIndexOutOfBoundsException if the file is too small, did some general clean-up.

Source here (if you have any changes, push them right to the GitHub repo/project.

package org.stackoverflowusers.file;

import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.text.ParseException;

/**
 * Represents a Windows shortcut (typically visible to Java only as a '.lnk' file).
 *
 * Retrieved 2011-09-23 from http://stackoverflow.com/questions/309495/windows-shortcut-lnk-parser-in-java/672775#672775
 * Originally called LnkParser
 *
 * Written by: (the stack overflow users, obviously!)
 *   Apache Commons VFS dependency removed by crysxd (why were we using that!?) https://github.com/crysxd
 *   Headerified, refactored and commented by Code Bling http://stackoverflow.com/users/675721/code-bling
 *   Network file support added by Stefan Cordes http://stackoverflow.com/users/81330/stefan-cordes
 *   Adapted by Sam Brightman http://stackoverflow.com/users/2492/sam-brightman
 *   Based on information in 'The Windows Shortcut File Format' by Jesse Hager <jessehager@iname.com>
 *   And somewhat based on code from the book 'Swing Hacks: Tips and Tools for Killer GUIs'
 *     by Joshua Marinacci and Chris Adamson
 *     ISBN: 0-596-00907-0
 *     http://www.oreilly.com/catalog/swinghks/
 */
public class WindowsShortcut
{
    private boolean isDirectory;
    private boolean isLocal;
    private String real_file;

    /**
     * Provides a quick test to see if this could be a valid link !
     * If you try to instantiate a new WindowShortcut and the link is not valid,
     * Exceptions may be thrown and Exceptions are extremely slow to generate,
     * therefore any code needing to loop through several files should first check this.
     *
     * @param file the potential link
     * @return true if may be a link, false otherwise
     * @throws IOException if an IOException is thrown while reading from the file
     */
    public static boolean isPotentialValidLink(File file) throws IOException {
        final int minimum_length = 0x64;
        InputStream fis = new FileInputStream(file);
        boolean isPotentiallyValid = false;
        try {
            isPotentiallyValid = file.isFile()
                && file.getName().toLowerCase().endsWith(".lnk")
                && fis.available() >= minimum_length
                && isMagicPresent(getBytes(fis, 32));
        } finally {
            fis.close();
        }
        return isPotentiallyValid;
    }

    public WindowsShortcut(File file) throws IOException, ParseException {
        InputStream in = new FileInputStream(file);
        try {
            parseLink(getBytes(in));
        } finally {
            in.close();
        }
    }

    /**
     * @return the name of the filesystem object pointed to by this shortcut
     */
    public String getRealFilename() {
        return real_file;
    }

    /**
     * Tests if the shortcut points to a local resource.
     * @return true if the 'local' bit is set in this shortcut, false otherwise
     */
    public boolean isLocal() {
        return isLocal;
    }

    /**
     * Tests if the shortcut points to a directory.
     * @return true if the 'directory' bit is set in this shortcut, false otherwise
     */
    public boolean isDirectory() {
        return isDirectory;
    }

    /**
     * Gets all the bytes from an InputStream
     * @param in the InputStream from which to read bytes
     * @return array of all the bytes contained in 'in'
     * @throws IOException if an IOException is encountered while reading the data from the InputStream
     */
    private static byte[] getBytes(InputStream in) throws IOException {
        return getBytes(in, null);
    }

    /**
     * Gets up to max bytes from an InputStream
     * @param in the InputStream from which to read bytes
     * @param max maximum number of bytes to read
     * @return array of all the bytes contained in 'in'
     * @throws IOException if an IOException is encountered while reading the data from the InputStream
     */
    private static byte[] getBytes(InputStream in, Integer max) throws IOException {
        // read the entire file into a byte buffer
        ByteArrayOutputStream bout = new ByteArrayOutputStream();
        byte[] buff = new byte[256];
        while (max == null || max > 0) {
            int n = in.read(buff);
            if (n == -1) {
                break;
            }
            bout.write(buff, 0, n);
            if (max != null)
                max -= n;
        }
        in.close();
        return bout.toByteArray();
    }

    private static boolean isMagicPresent(byte[] link) {
        final int magic = 0x0000004C;
        final int magic_offset = 0x00;
        return link.length >= 32 && bytesToDword(link, magic_offset) == magic;
    }

    /**
     * Gobbles up link data by parsing it and storing info in member fields
     * @param link all the bytes from the .lnk file
     */
    private void parseLink(byte[] link) throws ParseException {
        try {
            if (!isMagicPresent(link))
                throw new ParseException("Invalid shortcut; magic is missing", 0);

            // get the flags byte
            byte flags = link[0x14];

            // get the file attributes byte
            final int file_atts_offset = 0x18;
            byte file_atts = link[file_atts_offset];
            byte is_dir_mask = (byte)0x10;
            if ((file_atts & is_dir_mask) > 0) {
                isDirectory = true;
            } else {
                isDirectory = false;
            }

            // if the shell settings are present, skip them
            final int shell_offset = 0x4c;
            final byte has_shell_mask = (byte)0x01;
            int shell_len = 0;
            if ((flags & has_shell_mask) > 0) {
                // the plus 2 accounts for the length marker itself
                shell_len = bytesToWord(link, shell_offset) + 2;
            }

            // get to the file settings
            int file_start = 0x4c + shell_len;

            final int file_location_info_flag_offset_offset = 0x08;
            int file_location_info_flag = link[file_start + file_location_info_flag_offset_offset];
            isLocal = (file_location_info_flag & 2) == 0;
            // get the local volume and local system values
            //final int localVolumeTable_offset_offset = 0x0C;
            final int basename_offset_offset = 0x10;
            final int networkVolumeTable_offset_offset = 0x14;
            final int finalname_offset_offset = 0x18;
            int finalname_offset = link[file_start + finalname_offset_offset] + file_start;
            String finalname = getNullDelimitedString(link, finalname_offset);
            if (isLocal) {
                int basename_offset = link[file_start + basename_offset_offset] + file_start;
                String basename = getNullDelimitedString(link, basename_offset);
                real_file = basename + finalname;
            } else {
                int networkVolumeTable_offset = link[file_start + networkVolumeTable_offset_offset] + file_start;
                int shareName_offset_offset = 0x08;
                int shareName_offset = link[networkVolumeTable_offset + shareName_offset_offset]
                    + networkVolumeTable_offset;
                String shareName = getNullDelimitedString(link, shareName_offset);
                real_file = shareName + "\\" + finalname;
            }
        } catch (ArrayIndexOutOfBoundsException e) {
            throw new ParseException("Could not be parsed, probably not a valid WindowsShortcut", 0);
        }
    }

    private static String getNullDelimitedString(byte[] bytes, int off) {
        int len = 0;
        // count bytes until the null character (0)
        while (true) {
            if (bytes[off + len] == 0) {
                break;
            }
            len++;
        }
        return new String(bytes, off, len);
    }

    /*
     * convert two bytes into a short note, this is little endian because it's
     * for an Intel only OS.
     */
    private static int bytesToWord(byte[] bytes, int off) {
        return ((bytes[off + 1] & 0xff) << 8) | (bytes[off] & 0xff);
    }

    private static int bytesToDword(byte[] bytes, int off) {
        return (bytesToWord(bytes, off + 2) << 16) | bytesToWord(bytes, off);
    }

}