Loader.java

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package com.google.ortools;
 
import com.sun.jna.Platform;
import java.io.IOException;
import java.net.URI;
import java.net.URISyntaxException;
import java.net.URL;
import java.nio.file.FileSystem;
import java.nio.file.FileSystems;
import java.nio.file.FileSystemAlreadyExistsException;
import java.nio.file.FileVisitResult;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.SimpleFileVisitor;
import java.nio.file.attribute.BasicFileAttributes;
import java.util.Collections;
import java.util.Objects;
 
public class Loader {
  private static URI getNativeResourceURI() throws IOException {
    ClassLoader loader = Loader.class.getClassLoader();
    String resource = Platform.RESOURCE_PREFIX + "/";
    URL resourceURL = loader.getResource(resource);
    Objects.requireNonNull(resourceURL,
        String.format("Resource %s was not found in ClassLoader %s", resource, loader));
 
    URI resourceURI;
    try {
      resourceURI = resourceURL.toURI();
    } catch (URISyntaxException e) {
      throw new IOException(e);
    }
    return resourceURI;
  }
 
  @FunctionalInterface
  private interface PathConsumer<T extends IOException> {
    void accept(Path path) throws T;
  }
 
  private static Path unpackNativeResources(URI resourceURI) throws IOException {
    Path tempPath;
    tempPath = Files.createTempDirectory("ortools-java");
    tempPath.toFile().deleteOnExit();
 
    PathConsumer<?> visitor;
    visitor = (Path sourcePath) -> Files.walkFileTree(sourcePath, new SimpleFileVisitor<Path>() {
      @Override
      public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) throws IOException {
        Path newPath = tempPath.resolve(sourcePath.getParent().relativize(file).toString());
        Files.copy(file, newPath);
        newPath.toFile().deleteOnExit();
        return FileVisitResult.CONTINUE;
      }
 
      @Override
      public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs)
          throws IOException {
        Path newPath = tempPath.resolve(sourcePath.getParent().relativize(dir).toString());
        Files.copy(dir, newPath);
        newPath.toFile().deleteOnExit();
        return FileVisitResult.CONTINUE;
      }
    });
 
    FileSystem fs;
    try {
      fs = FileSystems.newFileSystem(resourceURI, Collections.emptyMap());
    } catch (FileSystemAlreadyExistsException e) {
      fs = FileSystems.getFileSystem(resourceURI);
      if (fs == null) {
        throw new IllegalArgumentException();
      }
    }
    Path p = fs.provider().getPath(resourceURI);
    visitor.accept(p);
    return tempPath;
  }
 
  private static boolean loaded = false;
  public static void loadNativeLibraries() {
    if (!loaded) {
      try {
        URI resourceURI = getNativeResourceURI();
        Path tempPath = unpackNativeResources(resourceURI);
        // Load the native library
        System.load(tempPath.resolve(Platform.RESOURCE_PREFIX)
                        .resolve(System.mapLibraryName("jniortools"))
                        .toString());
        loaded = true;
      } catch (IOException e) {
        throw new RuntimeException(e);
      }
    }
  }
}