PseudoJar.java

package org.bndtools.utils.jar;

import java.io.Closeable;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.util.Arrays;
import java.util.Comparator;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.jar.JarEntry;
import java.util.jar.JarInputStream;
import java.util.jar.Manifest;

import aQute.lib.io.IO;

/**
 * A utility for reading either JAR files or directories that have the same layout as a JAR file.
 */
public class PseudoJar implements Closeable {

    private final File base;

    private JarInputStream jarStream = null;
    private Iterator<String> dirIndex = null;

    private JarEntry lastJarEntry = null;
    private String lastIndexEntry = null;

    public PseudoJar(File file) {
        this.base = file;
    }

    private void initJarStream() throws IOException {
        if (jarStream != null)
            return;

        if (!base.isFile())
            throw new IOException("Cannot read as JAR, file does not exist or is not a plain file: " + base);

        jarStream = new JarInputStream(IO.stream(base));
    }

    private void initDirIndex() throws IOException {
        if (dirIndex != null)
            return;

        if (!base.isDirectory())
            throw new IOException("Cannot read as directory, does not exist or is not a plain directory: " + base);

        List<String> tmpIndex = new LinkedList<String>();
        index("", base, tmpIndex);
        dirIndex = tmpIndex.iterator();
    }

    private static void index(String prefix, File dir, List<String> index) {
        File[] children = dir.listFiles();
        Arrays.sort(children, new Comparator<File>() {
            @Override
            public int compare(File f1, File f2) {
                return f1.getName().compareTo(f2.getName());
            }
        });
        if (children != null)
            for (File child : children) {
                String path = prefix + child.getName();
                if (child.isDirectory())
                    path += "/";

                index.add(path);

                if (child.isDirectory())
                    index(path, child, index);
            }
    }

    public Manifest readManifest() throws IOException {
        final Manifest mf;

        if (base.isDirectory()) {
            try (InputStream in = IO.stream(new File(base, "META-INF/MANIFEST.MF"))) {
                mf = new Manifest(in);
            }
        } else {
            initJarStream();
            mf = jarStream.getManifest();
        }
        return mf;
    }

    public String nextEntry() throws IOException {
        String path;

        if (base.isDirectory()) {
            initDirIndex();
            path = dirIndex.hasNext() ? dirIndex.next() : null;
            lastIndexEntry = path;
        } else {
            initJarStream();

            lastJarEntry = jarStream.getNextJarEntry();
            path = lastJarEntry != null ? lastJarEntry.getName() : null;
        }

        return path;
    }

    public boolean isDirectoryEntry() {
        if (lastJarEntry != null)
            return lastJarEntry.isDirectory();

        if (lastIndexEntry != null)
            return lastIndexEntry.endsWith("/");

        throw new IllegalStateException("No entry is current");
    }

    public InputStream openEntry() throws IOException {
        final InputStream result;

        if (jarStream != null) {
            if (lastJarEntry == null)
                throw new IOException("No more entries available");
            result = new InputStream() {
                @Override
                public int read() throws IOException {
                    return jarStream.read();
                }

                @Override
                public int read(byte[] b) throws IOException {
                    return jarStream.read(b);
                }

                @Override
                public int read(byte[] b, int off, int len) throws IOException {
                    return jarStream.read(b, off, len);
                }

                @Override
                public void close() throws IOException {
                    // swallow the close, which would otherwise close the whole JAR stream
                }
            };
        } else {
            if (lastIndexEntry == null)
                throw new IOException("No more entries available");
            result = IO.stream(new File(base, lastIndexEntry));
        }

        return result;
    }

    @Override
    public void close() throws IOException {
        if (jarStream != null)
            jarStream.close();
    }

}