native-utils/NativeUtils.java

/*
 * Class NativeUtils is published under the The MIT License:
 *
 * Copyright (c) 2012 Adam Heinrich <adam@adamh.cz>
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */
package cz.adamh.utils;
 
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
 
/**
 * A simple library class which helps with loading dynamic libraries stored in the
 * JAR archive. These libraries usualy contain implementation of some methods in
 * native code (using JNI - Java Native Interface).
 * 
 * @see http://adamheinrich.com/blog/2012/how-to-load-native-jni-library-from-jar
 * @see https://github.com/adamheinrich/native-utils
 *
 */
public class NativeUtils {
 
    /**
     * Private constructor - this class will never be instanced
     */
    private NativeUtils() {
    }
 
    /**
     * Loads library from current JAR archive
     * 
     * The file from JAR is copied into system temporary directory and then loaded. The temporary file is deleted after exiting.
     * Method uses String as filename because the pathname is "abstract", not system-dependent.
     * 
     * @param filename The filename inside JAR as absolute path (beginning with '/'), e.g. /package/File.ext
     * @throws IOException If temporary file creation or read/write operation fails
     * @throws IllegalArgumentException If source file (param path) does not exist
     * @throws IllegalArgumentException If the path is not absolute or if the filename is shorter than three characters (restriction of {@see File#createTempFile(java.lang.String, java.lang.String)}).
     */
    public static void loadLibraryFromJar(String path) throws IOException {
 
        if (!path.startsWith("/")) {
            throw new IllegalArgumentException("The path has to be absolute (start with '/').");
        }
 
        // Obtain filename from path
        String[] parts = path.split("/");
        String filename = (parts.length > 1) ? parts[parts.length - 1] : null;
 
        // Split filename to prexif and suffix (extension)
        String prefix = "";
        String suffix = null;
        if (filename != null) {
            parts = filename.split("\\.", 2);
            prefix = parts[0];
            suffix = (parts.length > 1) ? "."+parts[parts.length - 1] : null; // Thanks, davs! :-)
        }
 
        // Check if the filename is okay
        if (filename == null || prefix.length() < 3) {
            throw new IllegalArgumentException("The filename has to be at least 3 characters long.");
        }
 
        // Prepare temporary file
        File temp = File.createTempFile(prefix, suffix);
        temp.deleteOnExit();
 
        if (!temp.exists()) {
            throw new FileNotFoundException("File " + temp.getAbsolutePath() + " does not exist.");
        }
 
        // Prepare buffer for data copying
        byte[] buffer = new byte[1024];
        int readBytes;
 
        // Open and check input stream
        InputStream is = NativeUtils.class.getResourceAsStream(path);
        if (is == null) {
            throw new FileNotFoundException("File " + path + " was not found inside JAR.");
        }
 
        // Open output stream and copy data between source file in JAR and the temporary file
        OutputStream os = new FileOutputStream(temp);
        try {
            while ((readBytes = is.read(buffer)) != -1) {
                os.write(buffer, 0, readBytes);
            }
        } finally {
            // If read/write fails, close streams safely before throwing an exception
            os.close();
            is.close();
        }
 
        // Finally, load the library
        System.load(temp.getAbsolutePath());
    }
}