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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 java.io.IOException;
import java.io.Reader;

/**
 * A reader that imposes a limit to the number of characters that can be read from
 * an underlying reader, returning eof when this limit is reached -regardless of state of
 * underlying reader.
 *
 * 

* One use case is to avoid overrunning the readAheadLimit supplied to * java.io.Reader#mark(int), since reading too many characters removes the * ability to do a successful reset. *

* * @since 2.5 */ public class BoundedReader extends Reader { private static final int INVALID = -1; private final Reader target; private int charsRead = 0; private int markedAt = INVALID; private int readAheadLimit; // Internally, this value will never exceed the allowed size private final int maxCharsFromTargetReader; /** * Constructs a bounded reader * * @param target The target stream that will be used * @param maxCharsFromTargetReader The maximum number of characters that can be read from target * @throws IOException if mark fails */ public BoundedReader( final Reader target, final int maxCharsFromTargetReader ) throws IOException { this.target = target; this.maxCharsFromTargetReader = maxCharsFromTargetReader; } /** * Closes the target * * @throws IOException If an I/O error occurs while calling the underlying reader's close method */ @Override public void close() throws IOException { target.close(); } /** * Resets the target to the latest mark, * * @throws IOException If an I/O error occurs while calling the underlying reader's reset method * @see java.io.Reader#reset() */ @Override public void reset() throws IOException { charsRead = markedAt; target.reset(); } /** * marks the target stream * * @param readAheadLimit The number of characters that can be read while * still retaining the ability to do #reset(). * Note that this parameter is not validated with respect to * maxCharsFromTargetReader. There is no way to pass * past maxCharsFromTargetReader, even if this value is * greater. * * @throws IOException If an I/O error occurs while calling the underlying reader's mark method * @see java.io.Reader#mark(int) */ @Override public void mark( final int readAheadLimit ) throws IOException { this.readAheadLimit = readAheadLimit - charsRead; markedAt = charsRead; target.mark( readAheadLimit ); } /** * Reads a single character * * @return -1 on eof or the character read * @throws IOException If an I/O error occurs while calling the underlying reader's read method * @see java.io.Reader#read() */ @Override public int read() throws IOException { if ( charsRead >= maxCharsFromTargetReader ) { return -1; } if ( markedAt >= 0 && ( charsRead - markedAt ) >= readAheadLimit ) { return -1; } charsRead++; return target.read(); } /** * Reads into an array * * @param cbuf The buffer to fill * @param off The offset * @param len The number of chars to read * @return the number of chars read * @throws IOException If an I/O error occurs while calling the underlying reader's read method * @see java.io.Reader#read(char[], int, int) */ @Override public int read( final char[] cbuf, final int off, final int len ) throws IOException { int c; for ( int i = 0; i < len; i++ ) { c = read(); if ( c == -1 ) { return i == 0 ? -1 : i; } cbuf[off + i] = (char) c; } return len; } }




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