Java tutorial
/* * 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.IOException; import java.io.InputStream; import java.nio.ByteBuffer; import java.nio.CharBuffer; import java.nio.charset.CharacterCodingException; import java.nio.charset.Charset; import java.nio.charset.CharsetEncoder; import java.nio.charset.CoderResult; import java.nio.charset.CodingErrorAction; /** * {@link InputStream} implementation that can read from String, StringBuffer, * StringBuilder or CharBuffer. * <p> * <strong>Note:</strong> Supports {@link #mark(int)} and {@link #reset()}. * * @since 2.2 */ public class CharSequenceInputStream extends InputStream { private static final int BUFFER_SIZE = 2048; private static final int NO_MARK = -1; private final CharsetEncoder encoder; private final CharBuffer cbuf; private final ByteBuffer bbuf; private int mark_cbuf; // position in cbuf private int mark_bbuf; // position in bbuf /** * Constructor. * * @param cs the input character sequence * @param charset the character set name to use * @param bufferSize the buffer size to use. * @throws IllegalArgumentException if the buffer is not large enough to hold a complete character */ public CharSequenceInputStream(final CharSequence cs, final Charset charset, final int bufferSize) { super(); this.encoder = charset.newEncoder().onMalformedInput(CodingErrorAction.REPLACE) .onUnmappableCharacter(CodingErrorAction.REPLACE); // Ensure that buffer is long enough to hold a complete character final float maxBytesPerChar = encoder.maxBytesPerChar(); if (bufferSize < maxBytesPerChar) { throw new IllegalArgumentException( "Buffer size " + bufferSize + " is less than maxBytesPerChar " + maxBytesPerChar); } this.bbuf = ByteBuffer.allocate(bufferSize); this.bbuf.flip(); this.cbuf = CharBuffer.wrap(cs); this.mark_cbuf = NO_MARK; this.mark_bbuf = NO_MARK; } /** * Constructor, calls {@link #CharSequenceInputStream(CharSequence, Charset, int)}. * * @param cs the input character sequence * @param charset the character set name to use * @param bufferSize the buffer size to use. * @throws IllegalArgumentException if the buffer is not large enough to hold a complete character */ public CharSequenceInputStream(final CharSequence cs, final String charset, final int bufferSize) { this(cs, Charset.forName(charset), bufferSize); } /** * Constructor, calls {@link #CharSequenceInputStream(CharSequence, Charset, int)} * with a buffer size of 2048. * * @param cs the input character sequence * @param charset the character set name to use * @throws IllegalArgumentException if the buffer is not large enough to hold a complete character */ public CharSequenceInputStream(final CharSequence cs, final Charset charset) { this(cs, charset, BUFFER_SIZE); } /** * Constructor, calls {@link #CharSequenceInputStream(CharSequence, String, int)} * with a buffer size of 2048. * * @param cs the input character sequence * @param charset the character set name to use * @throws IllegalArgumentException if the buffer is not large enough to hold a complete character */ public CharSequenceInputStream(final CharSequence cs, final String charset) { this(cs, charset, BUFFER_SIZE); } /** * Fills the byte output buffer from the input char buffer. * * @throws CharacterCodingException * an error encoding data */ private void fillBuffer() throws CharacterCodingException { this.bbuf.compact(); final CoderResult result = this.encoder.encode(this.cbuf, this.bbuf, true); if (result.isError()) { result.throwException(); } this.bbuf.flip(); } @Override public int read(final byte[] b, int off, int len) throws IOException { if (b == null) { throw new NullPointerException("Byte array is null"); } if (len < 0 || (off + len) > b.length) { throw new IndexOutOfBoundsException("Array Size=" + b.length + ", offset=" + off + ", length=" + len); } if (len == 0) { return 0; // must return 0 for zero length read } if (!this.bbuf.hasRemaining() && !this.cbuf.hasRemaining()) { return EOF; } int bytesRead = 0; while (len > 0) { if (this.bbuf.hasRemaining()) { final int chunk = Math.min(this.bbuf.remaining(), len); this.bbuf.get(b, off, chunk); off += chunk; len -= chunk; bytesRead += chunk; } else { fillBuffer(); if (!this.bbuf.hasRemaining() && !this.cbuf.hasRemaining()) { break; } } } return bytesRead == 0 && !this.cbuf.hasRemaining() ? EOF : bytesRead; } @Override public int read() throws IOException { for (;;) { if (this.bbuf.hasRemaining()) { return this.bbuf.get() & 0xFF; } fillBuffer(); if (!this.bbuf.hasRemaining() && !this.cbuf.hasRemaining()) { return EOF; } } } @Override public int read(final byte[] b) throws IOException { return read(b, 0, b.length); } @Override public long skip(long n) throws IOException { /* * This could be made more efficient by using position to skip within the current buffer. */ long skipped = 0; while (n > 0 && available() > 0) { this.read(); n--; skipped++; } return skipped; } /** * Return an estimate of the number of bytes remaining in the byte stream. * @return the count of bytes that can be read without blocking (or returning EOF). * * @throws IOException if an error occurs (probably not possible) */ @Override public int available() throws IOException { // The cached entries are in bbuf; since encoding always creates at least one byte // per character, we can add the two to get a better estimate (e.g. if bbuf is empty) // Note that the previous implementation (2.4) could return zero even though there were // encoded bytes still available. return this.bbuf.remaining() + this.cbuf.remaining(); } @Override public void close() throws IOException { } /** * {@inheritDoc} * @param readlimit max read limit (ignored) */ @Override public synchronized void mark(final int readlimit) { this.mark_cbuf = this.cbuf.position(); this.mark_bbuf = this.bbuf.position(); this.cbuf.mark(); this.bbuf.mark(); // It would be nice to be able to use mark & reset on the cbuf and bbuf; // however the bbuf is re-used so that won't work } @Override public synchronized void reset() throws IOException { /* * This is not the most efficient implementation, as it re-encodes from the beginning. * * Since the bbuf is re-used, in general it's necessary to re-encode the data. * * It should be possible to apply some optimisations however: * + use mark/reset on the cbuf and bbuf. This would only work if the buffer had not been (re)filled since * the mark. The code would have to catch InvalidMarkException - does not seem possible to check if mark is * valid otherwise. + Try saving the state of the cbuf before each fillBuffer; it might be possible to * restart from there. */ if (this.mark_cbuf != NO_MARK) { // if cbuf is at 0, we have not started reading anything, so skip re-encoding if (this.cbuf.position() != 0) { this.encoder.reset(); this.cbuf.rewind(); this.bbuf.rewind(); this.bbuf.limit(0); // rewind does not clear the buffer while (this.cbuf.position() < this.mark_cbuf) { this.bbuf.rewind(); // empty the buffer (we only refill when empty during normal processing) this.bbuf.limit(0); fillBuffer(); } } if (this.cbuf.position() != this.mark_cbuf) { throw new IllegalStateException("Unexpected CharBuffer postion: actual=" + cbuf.position() + " " + "expected=" + this.mark_cbuf); } this.bbuf.position(this.mark_bbuf); this.mark_cbuf = NO_MARK; this.mark_bbuf = NO_MARK; } } @Override public boolean markSupported() { return true; } }