OpenJDK 8 Code Samples

OpenJDK Developers Guide

Try - With - Resource: Example 1

		
			
import java.io.BufferedOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.io.PrintStream;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;

/**
 * This sample demonstrates the ability to create custom resource that
 * implements the {@code AutoCloseable} interface. This resource can be used in
 * the try-with-resources construct.
 */
public class CustomAutoCloseableSample {

    /**
     * The main method for the CustomAutoCloseableSample program.
     *
     * @param args is not used.
     */
    public static void main(String[] args) {
        /*
         * TeeStream will be closed automatically after the try block.
         */
        try (TeeStream teeStream = new TeeStream(System.out, Paths.get("out.txt"));
             PrintStream out = new PrintStream(teeStream)) {
            out.print("Hello, world");
        } catch (Exception e) {
            e.printStackTrace();
            System.exit(1);
        }
    }

    /**
     * Passes the output through to the specified output stream while copying it into a file.
     * The TeeStream functionality is similar to the Unix tee utility.
     * TeeStream implements AutoCloseable interface. See OutputStream for details.
     */
    public static class TeeStream extends OutputStream {

        private final OutputStream fileStream;
        private final OutputStream outputStream;

        /**
         * Creates a TeeStream.
         *
         * @param outputStream an output stream.
         * @param outputFile   an path to file.
         * @throws IOException If an I/O error occurs.
         */
        public TeeStream(OutputStream outputStream, Path outputFile) throws IOException {
            this.fileStream = new BufferedOutputStream(Files.newOutputStream(outputFile));
            this.outputStream = outputStream;
        }

        /**
         * Writes the specified byte to the specified output stream
         * and copies it to the file.
         *
         * @param b the byte to be written.
         * @throws IOException If an I/O error occurs.
         */
        @Override
        public void write(int b) throws IOException {
            fileStream.write(b);
            outputStream.write(b);
        }

        /**
         * Flushes this output stream and forces any buffered output bytes
         * to be written out.
         * The flush method of TeeStream flushes
         * the specified output stream and the file output stream.
         *
         * @throws IOException if an I/O error occurs.
         */
        @Override
        public void flush() throws IOException {
            outputStream.flush();
            fileStream.flush();
        }

        /**
         * Closes underlying streams and resources.
         * The external output stream won't be closed.
         * This method is the member of AutoCloseable interface and
         * it will be invoked automatically after the try-with-resources block.
         *
         * @throws IOException If an I/O error occurs.
         */
        @Override
        public void close() throws IOException {
            try (OutputStream file = fileStream) {
                flush();
            }
        }
    }
}

			
			
	

Try - With - Resource : Example 2

		
			
/**
 * Extract (unzip) a file to the current directory.
 */
public class Unzip {

    /**
     * The main method for the Unzip program. Run the program with an empty
     * argument list to see possible arguments.
     *
     * @param args the argument list for {@code Unzip}.
     */
    public static void main(String[] args) {
        if (args.length != 1) {
            System.out.println("Usage: Unzip zipfile");
        }
        final Path destDir = Paths.get(".");
        /*
         * Create AutoCloseable FileSystem. It will be closed automatically
         * after the try block.
         */
        try (FileSystem zipFileSystem = FileSystems.newFileSystem(Paths.get(args[0]), null)) {

            Path top = zipFileSystem.getPath("/");
            Files.walk(top).skip(1).forEach(file -> {
                Path target = destDir.resolve(top.relativize(file).toString());
                System.out.println("Extracting " + target);
                try {
                    Files.copy(file, target, REPLACE_EXISTING);
                } catch (IOException e) {
                    throw new UncheckedIOException(e);
                }
            });
        } catch (UncheckedIOException | IOException e) {
            e.printStackTrace();
            System.exit(1);
        }
    }
}


			
	

Try - With - Resource : Example 3

		
			
/**
 * Prints data of the specified file to standard output from a zip archive.
 */
public class ZipCat {

    /**
     * The main method for the ZipCat program. Run the program with an empty
     * argument list to see possible arguments.
     *
     * @param args the argument list for ZipCat
     */
    public static void main(String[] args) {
        if (args.length != 2) {
            System.out.println("Usage: ZipCat zipfile fileToPrint");
        }
        /*
         * Creates AutoCloseable FileSystem and BufferedReader.
         * They will be closed automatically after the try block.
         * If reader initialization fails, then zipFileSystem will be closed
         * automatically.
         */
        try (FileSystem zipFileSystem
                = FileSystems.newFileSystem(Paths.get(args[0]),null);
                InputStream input
                = Files.newInputStream(zipFileSystem.getPath(args[1]))) {
                    byte[] buffer = new byte[1024];
                    int len;
                    while ((len = input.read(buffer)) != -1) {
                        System.out.write(buffer, 0, len);
                    }

        } catch (IOException e) {
            e.printStackTrace();
            System.exit(1);
        }
    }
}


			
	

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