http://commons.apache.org/proper/commons-io/: The Apache Commons IO library contains utility classes, stream implementations, file filters, file comparators, endian transformation classes, and much more. (The Apache Software Foundation)
  • Rahul Akolkar
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/*
 * 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;


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 FilterInputStream
to increase reusability, because FilterInputStream changes the
methods being called, such as read(byte[]) to read(byte[], int, int).


See the protected methods for ways in which a subclass can easily decorate
a stream with custom pre-, post- or error processing functionality.

/**
 * 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.
 * <p>
 * It is an alternative base class to FilterInputStream
 * to increase reusability, because FilterInputStream changes the
 * methods being called, such as read(byte[]) to read(byte[], int, int).
 * <p>
 * See the protected methods for ways in which a subclass can easily decorate
 * a stream with custom pre-, post- or error processing functionality.
 *
 */
public abstract class ProxyInputStream extends FilterInputStream {

    
Constructs a new ProxyInputStream.

Params:
  • proxy –  the InputStream to delegate to
/**
     * 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'
    }

    
Invokes the delegate's read() method.

Throws:
Returns:the byte read or -1 if the end of stream
/**
     * Invokes the delegate's <code>read()</code> 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 read(byte[]) method.

Params:
  • bts – the buffer to read the bytes into
Throws:
Returns:the number of bytes read or EOF if the end of stream
/**
     * Invokes the delegate's <code>read(byte[])</code> method.
     * @param bts 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[] bts) throws IOException {
        try {
            beforeRead(bts != null ? bts.length : 0);
            final int n = in.read(bts);
            afterRead(n);
            return n;
        } catch (final IOException e) {
            handleIOException(e);
            return EOF;
        }
    }

    
Invokes the delegate's read(byte[], int, int) method.

Params:
  • bts – the buffer to read the bytes into
  • off – The start offset
  • len – The number of bytes to read
Throws:
Returns:the number of bytes read or -1 if the end of stream
/**
     * Invokes the delegate's <code>read(byte[], int, int)</code> method.
     * @param bts 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[] bts, final int off, final int len) throws IOException {
        try {
            beforeRead(len);
            final int n = in.read(bts, off, len);
            afterRead(n);
            return n;
        } catch (final IOException e) {
            handleIOException(e);
            return EOF;
        }
    }

    
Invokes the delegate's skip(long) method.

Params:
  • ln – the number of bytes to skip
Throws:
Returns:the actual number of bytes skipped
/**
     * Invokes the delegate's <code>skip(long)</code> method.
     * @param ln 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 ln) throws IOException {
        try {
            return in.skip(ln);
        } catch (final IOException e) {
            handleIOException(e);
            return 0;
        }
    }

    
Invokes the delegate's available() method.

Throws:
Returns:the number of available bytes
/**
     * Invokes the delegate's <code>available()</code> 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;
        }
    }

    
Invokes the delegate's close() method.

Throws:
  • IOException – if an I/O error occurs
/**
     * Invokes the delegate's <code>close()</code> method.
     * @throws IOException if an I/O error occurs
     */
    @Override
    public void close() throws IOException {
        try {
            in.close();
        } catch (final IOException e) {
            handleIOException(e);
        }
    }

    
Invokes the delegate's mark(int) method.

Params:
  • readlimit – read ahead limit
/**
     * Invokes the delegate's <code>mark(int)</code> method.
     * @param readlimit read ahead limit
     */
    @Override
    public synchronized void mark(final int readlimit) {
        in.mark(readlimit);
    }

    
Invokes the delegate's reset() method.

Throws:
  • IOException – if an I/O error occurs
/**
     * Invokes the delegate's <code>reset()</code> 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 markSupported() method.

Returns:true if mark is supported, otherwise false
/**
     * Invokes the delegate's <code>markSupported()</code> method.
     * @return true if mark is supported, otherwise false
     */
    @Override
    public boolean markSupported() {
        return in.markSupported();
    }

    
Invoked by the read methods before the call is proxied. The number of bytes that the caller wanted to read (1 for the read() method, buffer length for read(byte[]), etc.) is given as an argument. 

Subclasses can override this method to add common pre-processing
functionality without having to override all the read methods.
The default implementation does nothing.


Note this method is not called from skip(long) or reset(). You need to explicitly override those methods if you want to add pre-processing steps also to them. 
Params:
  • n – number of bytes that the caller asked to be read
Throws:
Since:2.0
/**
     * Invoked by the 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>
     * 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.
     *
     * @since 2.0
     * @param n number of bytes that the caller asked to be read
     * @throws IOException if the pre-processing fails
     */
    protected void beforeRead(final int n) throws IOException {
        // no-op
    }

    
Invoked by the 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.


Subclasses can override this method to add common post-processing
functionality without having to override all the read methods.
The default implementation does nothing.


Note this method is not called from skip(long) or reset(). You need to explicitly override those methods if you want to add post-processing steps also to them. 
Params:
  • n – number of bytes read, or -1 if the end of stream was reached
Throws:
Since:2.0
/**
     * Invoked by the 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>
     * 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.
     *
     * @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
     */
    protected void afterRead(final int n) throws IOException {
        // no-op
    }

    
Handle any IOExceptions thrown.


This method provides a point to implement custom exception
handling. The default behaviour is to re-throw the exception.

Params:
  • e – The IOException thrown
Throws:
Since:2.0
/**
     * Handle any IOExceptions thrown.
     * <p>
     * This method provides a point to implement custom exception
     * handling. The default behaviour 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;
    }

}