ProxyInputStream.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
*
* http://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.input;
import static org.apache.commons.io.IOUtils.EOF;
import java.io.FilterInputStream;
import java.io.IOException;
import java.io.InputStream;
import org.apache.commons.io.IOUtils;
/**
* A proxy stream which acts as a {@link FilterInputStream}, by passing all method calls on to the proxied stream, not changing which methods are called.
* <p>
* It is an alternative base class to {@link FilterInputStream} to increase reusability, because {@link FilterInputStream} changes the methods being called,
* such as read(byte[]) to read(byte[], int, int).
* </p>
* <p>
* In addition, this class allows you to:
* </p>
* <ul>
* <li>notify a subclass that <em>n</em> bytes are about to be read through {@link #beforeRead(int)}</li>
* <li>notify a subclass that <em>n</em> bytes were read through {@link #afterRead(int)}</li>
* <li>notify a subclass that an exception was caught through {@link #handleIOException(IOException)}</li>
* <li>{@link #unwrap()} itself</li>
* </ul>
* <p>
* This class does not add any state (no additional instance variables).
* </p>
*/
public abstract class ProxyInputStream extends FilterInputStream {
/**
* Constructs a new ProxyInputStream.
*
* @param proxy the InputStream to delegate to
*/
public ProxyInputStream(final InputStream proxy) {
super(proxy);
// the proxy is stored in a protected superclass variable named 'in'
}
/**
* Invoked by the {@code read} methods after the proxied call has returned
* successfully. The number of bytes returned to the caller (or -1 if
* the end of stream was reached) is given as an argument.
* <p>
* Subclasses can override this method to add common post-processing
* functionality without having to override all the read methods.
* The default implementation does nothing.
* </p>
* <p>
* Note this method is <em>not</em> called from {@link #skip(long)} or
* {@link #reset()}. You need to explicitly override those methods if
* you want to add post-processing steps also to them.
* </p>
*
* @since 2.0
* @param n number of bytes read, or -1 if the end of stream was reached.
* @throws IOException if the post-processing fails in a subclass.
*/
@SuppressWarnings("unused") // Possibly thrown from subclasses.
protected void afterRead(final int n) throws IOException {
// no-op default
}
/**
* Invokes the delegate's {@code available()} method.
*
* @return the number of available bytes
* @throws IOException if an I/O error occurs.
*/
@Override
public int available() throws IOException {
try {
return super.available();
} catch (final IOException e) {
handleIOException(e);
return 0;
}
}
/**
* Invoked by the {@code read} methods before the call is proxied. The number
* of bytes that the caller wanted to read (1 for the {@link #read()}
* method, buffer length for {@link #read(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 read methods.
* The default implementation does nothing.
* </p>
* <p>
* Note this method is <em>not</em> called from {@link #skip(long)} or
* {@link #reset()}. You need to explicitly override those methods if
* you want to add pre-processing steps also to them.
* </p>
*
* @since 2.0
* @param n number of bytes that the caller asked to be read.
* @throws IOException if the pre-processing fails in a subclass.
*/
@SuppressWarnings("unused") // Possibly thrown from subclasses.
protected void beforeRead(final int n) throws IOException {
// no-op default
}
/**
* Invokes the delegate's {@code close()} method.
*
* @throws IOException if an I/O error occurs.
*/
@Override
public void close() throws IOException {
IOUtils.close(in, this::handleIOException);
}
/**
* Handles any IOExceptions thrown; by default, throws the given exception.
* <p>
* This method provides a point to implement custom exception
* handling. The default behavior is to re-throw the exception.
* </p>
*
* @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;
}
/**
* Invokes the delegate's {@code mark(int)} method.
*
* @param readLimit read ahead limit
*/
@Override
public synchronized void mark(final int readLimit) {
in.mark(readLimit);
}
/**
* Invokes the delegate's {@code markSupported()} method.
*
* @return true if mark is supported, otherwise false
*/
@Override
public boolean markSupported() {
return in.markSupported();
}
/**
* Invokes the delegate's {@code read()} method.
*
* @return the byte read or -1 if the end of stream
* @throws IOException if an I/O error occurs.
*/
@Override
public int read() throws IOException {
try {
beforeRead(1);
final int b = in.read();
afterRead(b != EOF ? 1 : EOF);
return b;
} catch (final IOException e) {
handleIOException(e);
return EOF;
}
}
/**
* Invokes the delegate's {@code read(byte[])} method.
*
* @param b the buffer to read the bytes into
* @return the number of bytes read or EOF if the end of stream
* @throws IOException if an I/O error occurs.
*/
@Override
public int read(final byte[] b) throws IOException {
try {
beforeRead(IOUtils.length(b));
final int n = in.read(b);
afterRead(n);
return n;
} catch (final IOException e) {
handleIOException(e);
return EOF;
}
}
/**
* Invokes the delegate's {@code read(byte[], int, int)} method.
*
* @param b the buffer to read the bytes into
* @param off The start offset
* @param len The number of bytes to read
* @return the number of bytes read or -1 if the end of stream
* @throws IOException if an I/O error occurs.
*/
@Override
public int read(final byte[] b, final int off, final int len) throws IOException {
try {
beforeRead(len);
final int n = in.read(b, off, len);
afterRead(n);
return n;
} catch (final IOException e) {
handleIOException(e);
return EOF;
}
}
/**
* Invokes the delegate's {@code reset()} method.
*
* @throws IOException if an I/O error occurs.
*/
@Override
public synchronized void reset() throws IOException {
try {
in.reset();
} catch (final IOException e) {
handleIOException(e);
}
}
/**
* Invokes the delegate's {@code skip(long)} method.
*
* @param n the number of bytes to skip
* @return the actual number of bytes skipped
* @throws IOException if an I/O error occurs.
*/
@Override
public long skip(final long n) throws IOException {
try {
return in.skip(n);
} catch (final IOException e) {
handleIOException(e);
return 0;
}
}
/**
* Unwraps this instance by returning the underlying InputStream.
* <p>
* Use with caution; useful to query the underlying InputStream.
* </p>
* @return the underlying InputStream.
* @since 2.16.0
*/
public InputStream unwrap() {
return in;
}
}