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324 lines (301 loc) · 10.8 KB
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/*
* Copyright (c) 1996, 2024, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
package java.io;
import java.util.Arrays;
import java.util.Objects;
import jdk.internal.misc.VM;
/**
* Writes text to a character-output stream, buffering characters so as to
* provide for the efficient writing of single characters, arrays, and strings.
*
* <p> The buffer size may be specified, or the default size may be accepted.
* The default is large enough for most purposes.
*
* <p> A {@code newLine()} method is provided, which uses the platform's own
* notion of line separator as defined by the system property
* {@linkplain System#lineSeparator() line.separator}. Not all platforms use the newline character ('\n')
* to terminate lines. Calling this method to terminate each output line is
* therefore preferred to writing a newline character directly.
*
* <p> In general, a {@code Writer} sends its output immediately to the
* underlying character or byte stream. Unless prompt output is required, it
* is advisable to wrap a {@code BufferedWriter} around any {@code Writer} whose
* {@code write()} operations may be costly, such as {@code FileWriter}s and
* {@code OutputStreamWriter}s. For example,
*
* {@snippet lang=java :
* PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter("foo.out")));
* }
*
* will buffer the {@code PrintWriter}'s output to the file. Without buffering,
* each invocation of a {@code print()} method would cause characters to be
* converted into bytes that would then be written immediately to the file,
* which can be very inefficient.
*
* @apiNote
* Once wrapped in a {@code BufferedWriter}, the underlying
* {@code Writer} should not be used directly nor wrapped with
* another writer.
*
* @see PrintWriter
* @see FileWriter
* @see OutputStreamWriter
* @see java.nio.file.Files#newBufferedWriter
*
* @author Mark Reinhold
* @since 1.1
*/
public class BufferedWriter extends Writer {
private static final int DEFAULT_INITIAL_BUFFER_SIZE = 512;
private static final int DEFAULT_MAX_BUFFER_SIZE = 8192;
private Writer out;
private char[] cb;
private int nChars;
private int nextChar;
private final int maxChars; // maximum number of buffers chars
/**
* Returns the buffer size to use when no output buffer size specified
*/
private static int initialBufferSize() {
if (VM.isBooted() && Thread.currentThread().isVirtual()) {
return DEFAULT_INITIAL_BUFFER_SIZE;
} else {
return DEFAULT_MAX_BUFFER_SIZE;
}
}
/**
* Creates a buffered character-output stream.
*/
private BufferedWriter(Writer out, int initialSize, int maxSize) {
super(out);
if (initialSize <= 0) {
throw new IllegalArgumentException("Buffer size <= 0");
}
this.out = out;
this.cb = new char[initialSize];
this.nChars = initialSize;
this.maxChars = maxSize;
}
/**
* Creates a buffered character-output stream that uses a default-sized
* output buffer.
*
* @param out A Writer
*/
public BufferedWriter(Writer out) {
this(out, initialBufferSize(), DEFAULT_MAX_BUFFER_SIZE);
}
/**
* Creates a new buffered character-output stream that uses an output
* buffer of the given size.
*
* @param out A Writer
* @param sz Output-buffer size, a positive integer
*
* @throws IllegalArgumentException If {@code sz <= 0}
*/
public BufferedWriter(Writer out, int sz) {
this(out, sz, sz);
}
/** Checks to make sure that the stream has not been closed */
private void ensureOpen() throws IOException {
if (out == null)
throw new IOException("Stream closed");
}
/**
* Grow char array to fit an additional len characters if needed.
* If possible, it grows by len+1 to avoid flushing when len chars
* are added.
*
* This method should only be called while holding the lock.
*/
private void growIfNeeded(int len) {
int neededSize = nextChar + len + 1;
if (neededSize < 0)
neededSize = Integer.MAX_VALUE;
if (neededSize > nChars && nChars < maxChars) {
int newSize = min(neededSize, maxChars);
cb = Arrays.copyOf(cb, newSize);
nChars = newSize;
}
}
/**
* Flushes the output buffer to the underlying character stream, without
* flushing the stream itself. This method is non-private only so that it
* may be invoked by PrintStream.
*/
void flushBuffer() throws IOException {
synchronized (lock) {
ensureOpen();
if (nextChar == 0)
return;
out.write(cb, 0, nextChar);
nextChar = 0;
}
}
/**
* Writes a single character.
*
* @throws IOException If an I/O error occurs
*/
public void write(int c) throws IOException {
synchronized (lock) {
ensureOpen();
growIfNeeded(1);
if (nextChar >= nChars)
flushBuffer();
cb[nextChar++] = (char) c;
}
}
/**
* Our own little min method, to avoid loading java.lang.Math if we've run
* out of file descriptors and we're trying to print a stack trace.
*/
private int min(int a, int b) {
if (a < b) return a;
return b;
}
/**
* Writes a portion of an array of characters.
*
* <p> Ordinarily this method stores characters from the given array into
* this stream's buffer, flushing the buffer to the underlying stream as
* needed. If the requested length is at least as large as the buffer,
* however, then this method will flush the buffer and write the characters
* directly to the underlying stream. Thus redundant
* {@code BufferedWriter}s will not copy data unnecessarily.
*
* @param cbuf A character array
* @param off Offset from which to start reading characters
* @param len Number of characters to write
*
* @throws IndexOutOfBoundsException
* If {@code off} is negative, or {@code len} is negative,
* or {@code off + len} is negative or greater than the length
* of the given array
*
* @throws IOException If an I/O error occurs
*/
public void write(char[] cbuf, int off, int len) throws IOException {
synchronized (lock) {
ensureOpen();
Objects.checkFromIndexSize(off, len, cbuf.length);
if (len == 0) {
return;
}
if (len >= maxChars) {
/* If the request length exceeds the max size of the output buffer,
flush the buffer and then write the data directly. In this
way buffered streams will cascade harmlessly. */
flushBuffer();
out.write(cbuf, off, len);
return;
}
growIfNeeded(len);
int b = off, t = off + len;
while (b < t) {
int d = min(nChars - nextChar, t - b);
System.arraycopy(cbuf, b, cb, nextChar, d);
b += d;
nextChar += d;
if (nextChar >= nChars) {
flushBuffer();
}
}
}
}
/**
* Writes a portion of a String.
*
* @implSpec
* While the specification of this method in the
* {@linkplain java.io.Writer#write(java.lang.String,int,int) superclass}
* recommends that an {@link IndexOutOfBoundsException} be thrown
* if {@code len} is negative or {@code off + len} is negative,
* the implementation in this class does not throw such an exception in
* these cases but instead simply writes no characters.
*
* @param s String to be written
* @param off Offset from which to start reading characters
* @param len Number of characters to be written
*
* @throws IndexOutOfBoundsException
* If {@code off} is negative,
* or {@code off + len} is greater than the length
* of the given string
*
* @throws IOException If an I/O error occurs
*/
public void write(String s, int off, int len) throws IOException {
synchronized (lock) {
ensureOpen();
growIfNeeded(len);
int b = off, t = off + len;
while (b < t) {
int d = min(nChars - nextChar, t - b);
s.getChars(b, b + d, cb, nextChar);
b += d;
nextChar += d;
if (nextChar >= nChars)
flushBuffer();
}
}
}
/**
* Writes a line separator. The line separator string is defined by the
* system property {@code line.separator}, and is not necessarily a single
* newline ('\n') character.
*
* @throws IOException If an I/O error occurs
*/
public void newLine() throws IOException {
write(System.lineSeparator());
}
/**
* Flushes the stream.
*
* @throws IOException If an I/O error occurs
*/
public void flush() throws IOException {
synchronized (lock) {
flushBuffer();
out.flush();
}
}
@SuppressWarnings("try")
public void close() throws IOException {
synchronized (lock) {
if (out == null) {
return;
}
try (Writer w = out) {
flushBuffer();
} finally {
out = null;
cb = null;
}
}
}
}