ProxyOutputStream.java
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* https://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.commons.io.output;
import java.io.FilterOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import org.apache.commons.io.IOUtils;
import org.apache.commons.io.build.AbstractStreamBuilder;
/**
* A Proxy stream which acts as expected, that is it passes the method
* calls on to the proxied stream and doesn't change which methods are
* being called. It is an alternative base class to FilterOutputStream
* to increase reusability.
* <p>
* See the protected methods for ways in which a subclass can easily decorate
* a stream with custom pre-, post- or error processing functionality.
* </p>
*/
public class ProxyOutputStream extends FilterOutputStream {
/**
* Builds instances of {@link ProxyOutputStream}.
* <p>
* This class does not provide a convenience static {@code builder()} method so that subclasses can.
* </p>
*
* @since 2.19.0
*/
public static class Builder extends AbstractStreamBuilder<ProxyOutputStream, Builder> {
/**
* Constructs a new builder of {@link ProxyOutputStream}.
*/
public Builder() {
// empty
}
/**
* Builds a new {@link ProxyOutputStream}.
* <p>
* This builder uses the following aspects:
* </p>
* <ul>
* <li>{@link #getOutputStream()} is the target aspect.</li>
* </ul>
*
* @return a new instance.
* @throws IllegalStateException if the {@code origin} is {@code null}.
* @throws UnsupportedOperationException if the origin cannot be converted to an {@link OutputStream}.
* @throws IOException if an I/O error occurs converting to an {@link OutputStream} using {@link #getOutputStream()}.
* @see #getOutputStream()
* @see #getUnchecked()
*/
@SuppressWarnings("resource") // caller closes
@Override
public ProxyOutputStream get() throws IOException {
return new ProxyOutputStream(getOutputStream());
}
}
/**
* Constructs a new ProxyOutputStream.
*
* @param delegate the OutputStream to delegate to
*/
public ProxyOutputStream(final OutputStream delegate) {
// the delegate is stored in a protected superclass variable named 'out'
super(delegate);
}
/**
* Invoked by the write methods after the proxied call has returned
* successfully. The number of bytes written (1 for the
* {@link #write(int)} method, buffer length for {@link #write(byte[])},
* etc.) is given as an argument.
* <p>
* Subclasses can override this method to add common post-processing
* functionality without having to override all the write methods.
* The default implementation does nothing.
*
* @param n number of bytes written
* @throws IOException if the post-processing fails
* @since 2.0
*/
@SuppressWarnings("unused") // Possibly thrown from subclasses.
protected void afterWrite(final int n) throws IOException {
// noop
}
/**
* Invoked by the write methods before the call is proxied. The number
* of bytes to be written (1 for the {@link #write(int)} method, buffer
* length for {@link #write(byte[])}, etc.) is given as an argument.
* <p>
* Subclasses can override this method to add common pre-processing
* functionality without having to override all the write methods.
* The default implementation does nothing.
*
* @param n number of bytes to be written
* @throws IOException if the pre-processing fails
* @since 2.0
*/
@SuppressWarnings("unused") // Possibly thrown from subclasses.
protected void beforeWrite(final int n) throws IOException {
// noop
}
/**
* Invokes the delegate's {@code close()} method.
* @throws IOException if an I/O error occurs.
*/
@Override
public void close() throws IOException {
IOUtils.close(out, this::handleIOException);
}
/**
* Invokes the delegate's {@code flush()} method.
* @throws IOException if an I/O error occurs.
*/
@Override
public void flush() throws IOException {
try {
out.flush();
} catch (final IOException e) {
handleIOException(e);
}
}
/**
* Handle any IOExceptions thrown.
* <p>
* This method provides a point to implement custom exception
* handling. The default behavior is to re-throw the exception.
* @param e The IOException thrown
* @throws IOException if an I/O error occurs.
* @since 2.0
*/
protected void handleIOException(final IOException e) throws IOException {
throw e;
}
/**
* Sets the underlying output stream.
*
* @param out the underlying output stream.
* @return this instance.
* @since 2.19.0
*/
public ProxyOutputStream setReference(final OutputStream out) {
this.out = out;
return this;
}
/**
* Unwraps this instance by returning the underlying {@link OutputStream}.
* <p>
* Use with caution; useful to query the underlying {@link OutputStream}.
* </p>
*
* @return the underlying {@link OutputStream}.
*/
OutputStream unwrap() {
return out;
}
/**
* Invokes the delegate's {@code write(byte[])} method.
* @param bts the bytes to write
* @throws IOException if an I/O error occurs.
*/
@Override
public void write(final byte[] bts) throws IOException {
try {
final int len = IOUtils.length(bts);
beforeWrite(len);
out.write(bts);
afterWrite(len);
} catch (final IOException e) {
handleIOException(e);
}
}
/**
* Invokes the delegate's {@code write(byte[])} method.
* @param bts the bytes to write
* @param st The start offset
* @param end The number of bytes to write
* @throws IOException if an I/O error occurs.
*/
@Override
public void write(final byte[] bts, final int st, final int end) throws IOException {
try {
beforeWrite(end);
out.write(bts, st, end);
afterWrite(end);
} catch (final IOException e) {
handleIOException(e);
}
}
/**
* Invokes the delegate's {@code write(int)} method.
* @param b the byte to write
* @throws IOException if an I/O error occurs.
*/
@Override
public void write(final int b) throws IOException {
try {
beforeWrite(1);
out.write(b);
afterWrite(1);
} catch (final IOException e) {
handleIOException(e);
}
}
}