DelayedInputStream.java

import clojure.lang.Delay;

import java.io.IOException;
import java.io.InputStream;

/**
 * A lazily initialized InputStream using a Clojure delay.
 * 
 * Construct with a delay that returns an InputStream. This delay will not be derefed until the
 * DelayedInputStream is first accessed.
 */
public class DelayedInputStream extends InputStream {
    private Delay delay;
    private InputStream inputStream;

    public DelayedInputStream() {
        super();
    }

    public DelayedInputStream(Delay delay) {
        super();
        this.delay = delay;
        this.inputStream = null;
    }

    private InputStream getInputStream() {
        if (inputStream == null) {
            this.inputStream = (InputStream) this.delay.deref();
        }
        return this.inputStream;
    }

    @Override
    public int read() throws IOException {
        return getInputStream().read();
    }

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

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

    @Override
    public long skip(long n) throws IOException {
        return getInputStream().skip(n);
    }

    @Override
    public int available() throws IOException {
        return getInputStream().available();
    }

    @Override
    public void close() throws IOException {
        getInputStream().close();
    }

    @Override
    public synchronized void mark(int readlimit) {
        getInputStream().mark(readlimit);
    }

    @Override
    public synchronized void reset() throws IOException {
        getInputStream().reset();
    }

    @Override
    public boolean markSupported() {
        return getInputStream().markSupported();
    }
}