While the stream is open, the {@code append(char)}, {@code * append(CharSequence)}, {@code append(CharSequence, int, int)}, * {@code flush()}, {@code write(int)}, {@code write(char[])}, and * {@code write(char[], int, int)} methods do nothing. After the stream * has been closed, these methods all throw {@code IOException}. * *
The {@link #lock object} used to synchronize operations on the * returned {@code Writer} is not specified. * * @return a {@code Writer} which discards all characters * * @since 11 */ public static Writer nullWriter() { return new Writer() { private volatile boolean closed; private void ensureOpen() throws IOException { if (closed) { throw new IOException("Stream closed"); } } @Override public Writer append(char c) throws IOException { ensureOpen(); return this; } @Override public Writer append(CharSequence csq) throws IOException { ensureOpen(); return this; } @Override public Writer append(CharSequence csq, int start, int end) throws IOException { ensureOpen(); if (csq != null) { Objects.checkFromToIndex(start, end, csq.length()); } return this; } @Override public void write(int c) throws IOException { ensureOpen(); } @Override public void write(char[] cbuf, int off, int len) throws IOException { Objects.checkFromIndexSize(off, len, cbuf.length); ensureOpen(); } @Override public void write(String str) throws IOException { Objects.requireNonNull(str); ensureOpen(); } @Override public void write(String str, int off, int len) throws IOException { Objects.checkFromIndexSize(off, len, str.length()); ensureOpen(); } @Override public void flush() throws IOException { ensureOpen(); } @Override public void close() throws IOException { closed = true; } }; } /** * The object used to synchronize operations on this stream. For * efficiency, a character-stream object may use an object other than * itself to protect critical sections. A subclass should therefore use * the object in this field rather than {@code this} or a synchronized * method. */ protected Object lock; /** * Creates a new character-stream writer whose critical sections will * synchronize on the writer itself. */ protected Writer() { this.lock = this; } /** * Creates a new character-stream writer whose critical sections will * synchronize on the given object. * * @param lock * Object to synchronize on */ protected Writer(Object lock) { if (lock == null) { throw new NullPointerException(); } this.lock = lock; } /** * Writes a single character. The character to be written is contained in * the 16 low-order bits of the given integer value; the 16 high-order bits * are ignored. * *
Subclasses that intend to support efficient single-character output * should override this method. * * @param c * int specifying a character to be written * * @throws IOException * If an I/O error occurs */ public void write(int c) throws IOException { synchronized (lock) { if (writeBuffer == null){ writeBuffer = new char[WRITE_BUFFER_SIZE]; } writeBuffer[0] = (char) c; write(writeBuffer, 0, 1); } } /** * Writes an array of characters. * * @param cbuf * Array of characters to be written * * @throws IOException * If an I/O error occurs */ public void write(char[] cbuf) throws IOException { write(cbuf, 0, cbuf.length); } /** * Writes a portion of an array of characters. * * @param cbuf * Array of characters * * @param off * Offset from which to start writing characters * * @param len * Number of characters to write * * @throws IndexOutOfBoundsException * Implementations should throw this exception * 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 abstract void write(char[] cbuf, int off, int len) throws IOException; /** * Writes a string. * * @param str * String to be written * * @throws IOException * If an I/O error occurs */ public void write(String str) throws IOException { write(str, 0, str.length()); } /** * Writes a portion of a string. * * @implSpec * The implementation in this class throws an * {@code IndexOutOfBoundsException} for the indicated conditions; * overriding methods may choose to do otherwise. * * @param str * A String * * @param off * Offset from which to start writing characters * * @param len * Number of characters to write * * @throws IndexOutOfBoundsException * Implementations should throw this exception * if {@code off} is negative, or {@code len} is negative, * or {@code off + len} is negative or greater than the length * of the given string * * @throws IOException * If an I/O error occurs */ public void write(String str, int off, int len) throws IOException { synchronized (lock) { char[] cbuf; if (len <= WRITE_BUFFER_SIZE) { if (writeBuffer == null) { writeBuffer = new char[WRITE_BUFFER_SIZE]; } cbuf = writeBuffer; } else { // Don't permanently allocate very large buffers. cbuf = new char[len]; } str.getChars(off, (off + len), cbuf, 0); write(cbuf, 0, len); } } /** * Appends the specified character sequence to this writer. * *
An invocation of this method of the form {@code out.append(csq)} * behaves in exactly the same way as the invocation * *
* out.write(csq.toString())
*
* Depending on the specification of {@code toString} for the * character sequence {@code csq}, the entire sequence may not be * appended. For instance, invoking the {@code toString} method of a * character buffer will return a subsequence whose content depends upon * the buffer's position and limit. * * @param csq * The character sequence to append. If {@code csq} is * {@code null}, then the four characters {@code "null"} are * appended to this writer. * * @return This writer * * @throws IOException * If an I/O error occurs * * @since 1.5 */ public Writer append(CharSequence csq) throws IOException { write(String.valueOf(csq)); return this; } /** * Appends a subsequence of the specified character sequence to this writer. * {@code Appendable}. * *
An invocation of this method of the form * {@code out.append(csq, start, end)} when {@code csq} * is not {@code null} behaves in exactly the * same way as the invocation * *
{@code
* out.write(csq.subSequence(start, end).toString())
* }
*
* @param csq
* The character sequence from which a subsequence will be
* appended. If {@code csq} is {@code null}, then characters
* will be appended as if {@code csq} contained the four
* characters {@code "null"}.
*
* @param start
* The index of the first character in the subsequence
*
* @param end
* The index of the character following the last character in the
* subsequence
*
* @return This writer
*
* @throws IndexOutOfBoundsException
* If {@code start} or {@code end} are negative, {@code start}
* is greater than {@code end}, or {@code end} is greater than
* {@code csq.length()}
*
* @throws IOException
* If an I/O error occurs
*
* @since 1.5
*/
public Writer append(CharSequence csq, int start, int end) throws IOException {
if (csq == null) csq = "null";
return append(csq.subSequence(start, end));
}
/**
* Appends the specified character to this writer.
*
* An invocation of this method of the form {@code out.append(c)} * behaves in exactly the same way as the invocation * *
* out.write(c)
*
* @param c
* The 16-bit character to append
*
* @return This writer
*
* @throws IOException
* If an I/O error occurs
*
* @since 1.5
*/
public Writer append(char c) throws IOException {
write(c);
return this;
}
/**
* Flushes the stream. If the stream has saved any characters from the
* various write() methods in a buffer, write them immediately to their
* intended destination. Then, if that destination is another character or
* byte stream, flush it. Thus one flush() invocation will flush all the
* buffers in a chain of Writers and OutputStreams.
*
* If the intended destination of this stream is an abstraction provided * by the underlying operating system, for example a file, then flushing the * stream guarantees only that bytes previously written to the stream are * passed to the operating system for writing; it does not guarantee that * they are actually written to a physical device such as a disk drive. * * @throws IOException * If an I/O error occurs */ public abstract void flush() throws IOException; /** * Closes the stream, flushing it first. Once the stream has been closed, * further write() or flush() invocations will cause an IOException to be * thrown. Closing a previously closed stream has no effect. * * @throws IOException * If an I/O error occurs */ public abstract void close() throws IOException; }