panda.io.stream.ProxyInputStream Maven / Gradle / Ivy
package panda.io.stream;
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.
*/
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'
}
/**
* Invokes the delegate's 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 != -1 ? 1 : -1);
return b;
}
catch (final IOException e) {
handleIOException(e);
return -1;
}
}
/**
* Invokes the delegate's read(byte[]) method.
*
* @param bts the buffer to read the bytes into
* @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) 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 -1;
}
}
/**
* Invokes the delegate's read(byte[], int, int) 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 -1;
}
}
/**
* Invokes the delegate's skip(long) 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.
*
* @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
*/
@Override
public void close() throws IOException {
try {
in.close();
}
catch (final IOException e) {
handleIOException(e);
}
}
/**
* Invokes the delegate's mark(int) 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
*/
@Override
public synchronized void reset() throws IOException {
try {
in.reset();
}
catch (final IOException e) {
handleIOException(e);
}
}
/**
* Invokes the delegate's markSupported() 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 {@link #read()} method, buffer length for {@link #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 {@link #skip(long)} or {@link #reset()}. You
* need to explicitly override those methods if you want to add pre-processing steps also to
* them.
*
* @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 {
}
/**
* 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 {@link #skip(long)} or {@link #reset()}. You
* need to explicitly override those methods if you want to add post-processing steps also to
* them.
*
* @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 {
}
/**
* Handle any IOExceptions thrown.
*
* 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
*/
protected void handleIOException(final IOException e) throws IOException {
throw e;
}
}