org.apache.commons.io.input.ProxyReader Maven / Gradle / Ivy
/*
* 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.FilterReader;
import java.io.IOException;
import java.io.Reader;
import java.nio.CharBuffer;
/**
* 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 FilterReader
* to increase reusability, because FilterReader changes the
* methods being called, such as read(char[]) to read(char[], int, int).
*
*/
public abstract class ProxyReader extends FilterReader {
/**
* Constructs a new ProxyReader.
*
* @param proxy the Reader to delegate to
*/
public ProxyReader(final Reader proxy) {
super(proxy);
// the proxy is stored in a protected superclass variable named 'in'
}
/**
* Invokes the delegate's read() method.
* @return the character 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 c = in.read();
afterRead(c != EOF ? 1 : EOF);
return c;
} catch (final IOException e) {
handleIOException(e);
return EOF;
}
}
/**
* Invokes the delegate's read(char[]) method.
* @param chr the buffer to read the characters into
* @return the number of characters read or -1 if the end of stream
* @throws IOException if an I/O error occurs
*/
@Override
public int read(final char[] chr) throws IOException {
try {
beforeRead(chr != null ? chr.length : 0);
final int n = in.read(chr);
afterRead(n);
return n;
} catch (final IOException e) {
handleIOException(e);
return EOF;
}
}
/**
* Invokes the delegate's read(char[], int, int) method.
* @param chr the buffer to read the characters into
* @param st The start offset
* @param len The number of bytes to read
* @return the number of characters read or -1 if the end of stream
* @throws IOException if an I/O error occurs
*/
@Override
public int read(final char[] chr, final int st, final int len) throws IOException {
try {
beforeRead(len);
final int n = in.read(chr, st, len);
afterRead(n);
return n;
} catch (final IOException e) {
handleIOException(e);
return EOF;
}
}
/**
* Invokes the delegate's read(CharBuffer) method.
* @param target the char buffer to read the characters into
* @return the number of characters read or -1 if the end of stream
* @throws IOException if an I/O error occurs
* @since 2.0
*/
@Override
public int read(final CharBuffer target) throws IOException {
try {
beforeRead(target != null ? target.length() : 0);
final int n = in.read(target);
afterRead(n);
return n;
} catch (final IOException e) {
handleIOException(e);
return EOF;
}
}
/**
* Invokes the delegate's skip(long) method.
* @param ln the number of bytes to skip
* @return the number of bytes to skipped or EOF if the end of stream
* @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 ready() method.
* @return true if the stream is ready to be read
* @throws IOException if an I/O error occurs
*/
@Override
public boolean ready() throws IOException {
try {
return in.ready();
} catch (final IOException e) {
handleIOException(e);
return false;
}
}
/**
* 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 idx read ahead limit
* @throws IOException if an I/O error occurs
*/
@Override
public synchronized void mark(final int idx) throws IOException {
try {
in.mark(idx);
} catch (final IOException e) {
handleIOException(e);
}
}
/**
* 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 chars that the caller wanted to read (1 for the {@link #read()}
* method, buffer length for {@link #read(char[])}, 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.
*
* @since 2.0
* @param n number of chars 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 chars 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.
*
* @since 2.0
* @param n number of chars 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
* @since 2.0
*/
protected void handleIOException(final IOException e) throws IOException {
throw e;
}
}