Class ReferenceCountedJar

java/org/apache/tomcat/util/scan/ReferenceCountedJar.java:30–153

This class provides a wrapper around Jar that uses reference counting to close and re-create the wrapped Jar instance as required.

 * {@link Jar} instance as required.
 */
public class ReferenceCountedJar implements Jar {

    private final URL url;
    private Jar wrappedJar;
    private int referenceCount = 0;

    /**
     * Creates a new reference-counted wrapper for the JAR at the given URL.
     *
     * @param url the URL of the JAR file
     *
     * @throws IOException if the JAR cannot be opened
     */
    public ReferenceCountedJar(URL url) throws IOException {
        this.url = url;
        open();
    }


    /*
     * Note: Returns this instance so it can be used with try-with-resources
     */
    private synchronized ReferenceCountedJar open() throws IOException {
        if (wrappedJar == null) {
            wrappedJar = JarFactory.newInstance(url);
        }
        referenceCount++;
        return this;
    }


    @Override
    public synchronized void close() {
        referenceCount--;
        if (referenceCount == 0) {
            wrappedJar.close();
            wrappedJar = null;
        }
    }


    @Override
    public URL getJarFileURL() {
        return url;
    }


    @Override
    public InputStream getInputStream(String name) throws IOException {
        try (ReferenceCountedJar jar = open()) {
            return jar.wrappedJar.getInputStream(name);
        }
    }


    @Override
    public long getLastModified(String name) throws IOException {
        try (ReferenceCountedJar jar = open()) {