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SciJava Common is a shared library for SciJava software. It provides a plugin framework, with an extensible mechanism for service discovery, backed by its own annotation processor, so that plugins can be loaded dynamically. It is used by downstream projects in the SciJava ecosystem, such as ImageJ and SCIFIO.

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package org.scijava.io.handle;

import java.io.IOException;

import org.scijava.io.location.Location;

/**
 * Abstract superclass for {@link DataHandle}s that operate over other
 * {@link DataHandle}s.
 *
 * @author Gabriel Einsdorf
 */
public abstract class AbstractHigherOrderHandle extends
	AbstractDataHandle
{

	private DataHandle handle;
	private boolean closed;

	public AbstractHigherOrderHandle(final DataHandle handle) {
		this.handle = handle;
		set(handle.get()); // provides access to underlying location
	}

	@Override
	public boolean isReadable() {
		return !closed && handle.isReadable();
	}

	@Override
	public boolean isWritable() {
		return !closed && handle.isWritable();
	}

	@Override
	public long length() throws IOException {
		ensureOpen();
		return handle.length();
	}

	@Override
	public Class getType() {
		return handle.getType();
	}

	@Override
	public boolean exists() throws IOException {
		return handle.exists();
	}

	@Override
	public void close() throws IOException {
		if (!closed) {
			cleanup();
			closed = true;
			handle.close();
			handle = null;
		}
	}

	protected void ensureOpen() throws IOException {
		if (closed) {
			throw new IOException("This handle is closed!");
		}
	}

	/**
	 * Clean up data structures after a handle has been closed in the
	 * {@link #close()} method.
	 *
	 * @throws IOException
	 */
	protected abstract void cleanup() throws IOException;

	/**
	 * @return the {@link DataHandle} wrapped by this
	 *         {@link AbstractHigherOrderHandle}
	 */
	protected DataHandle handle() {
		return handle;
	}

}