Java tutorial
/* * Copyright (c) 1994, 2019, 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; /** * A data output stream lets an application write primitive Java data * types to an output stream in a portable way. An application can * then use a data input stream to read the data back in. * * @author unascribed * @see java.io.DataInputStream * @since 1.0 */ public class DataOutputStream extends FilterOutputStream implements DataOutput { /** * The number of bytes written to the data output stream so far. * If this counter overflows, it will be wrapped to Integer.MAX_VALUE. */ protected int written; /** * bytearr is initialized on demand by writeUTF */ private byte[] bytearr = null; /** * Creates a new data output stream to write data to the specified * underlying output stream. The counter <code>written</code> is * set to zero. * * @param out the underlying output stream, to be saved for later * use. * @see java.io.FilterOutputStream#out */ public DataOutputStream(OutputStream out) { super(out); } /** * Increases the written counter by the specified value * until it reaches Integer.MAX_VALUE. */ private void incCount(int value) { int temp = written + value; if (temp < 0) { temp = Integer.MAX_VALUE; } written = temp; } /** * Writes the specified byte (the low eight bits of the argument * <code>b</code>) to the underlying output stream. If no exception * is thrown, the counter <code>written</code> is incremented by * <code>1</code>. * <p> * Implements the <code>write</code> method of <code>OutputStream</code>. * * @param b the <code>byte</code> to be written. * @exception IOException if an I/O error occurs. * @see java.io.FilterOutputStream#out */ public synchronized void write(int b) throws IOException { out.write(b); incCount(1); } /** * Writes <code>len</code> bytes from the specified byte array * starting at offset <code>off</code> to the underlying output stream. * If no exception is thrown, the counter <code>written</code> is * incremented by <code>len</code>. * * @param b the data. * @param off the start offset in the data. * @param len the number of bytes to write. * @exception IOException if an I/O error occurs. * @see java.io.FilterOutputStream#out */ public synchronized void write(byte b[], int off, int len) throws IOException { out.write(b, off, len); incCount(len); } /** * Flushes this data output stream. This forces any buffered output * bytes to be written out to the stream. * <p> * The <code>flush</code> method of <code>DataOutputStream</code> * calls the <code>flush</code> method of its underlying output stream. * * @exception IOException if an I/O error occurs. * @see java.io.FilterOutputStream#out * @see java.io.OutputStream#flush() */ public void flush() throws IOException { out.flush(); } /** * Writes a <code>boolean</code> to the underlying output stream as * a 1-byte value. The value <code>true</code> is written out as the * value <code>(byte)1</code>; the value <code>false</code> is * written out as the value <code>(byte)0</code>. If no exception is * thrown, the counter <code>written</code> is incremented by * <code>1</code>. * * @param v a <code>boolean</code> value to be written. * @exception IOException if an I/O error occurs. * @see java.io.FilterOutputStream#out */ public final void writeBoolean(boolean v) throws IOException { out.write(v ? 1 : 0); incCount(1); } /** * Writes out a <code>byte</code> to the underlying output stream as * a 1-byte value. If no exception is thrown, the counter * <code>written</code> is incremented by <code>1</code>. * * @param v a <code>byte</code> value to be written. * @exception IOException if an I/O error occurs. * @see java.io.FilterOutputStream#out */ public final void writeByte(int v) throws IOException { out.write(v); incCount(1); } /** * Writes a <code>short</code> to the underlying output stream as two * bytes, high byte first. If no exception is thrown, the counter * <code>written</code> is incremented by <code>2</code>. * * @param v a <code>short</code> to be written. * @exception IOException if an I/O error occurs. * @see java.io.FilterOutputStream#out */ public final void writeShort(int v) throws IOException { out.write((v >>> 8) & 0xFF); out.write((v >>> 0) & 0xFF); incCount(2); } /** * Writes a <code>char</code> to the underlying output stream as a * 2-byte value, high byte first. If no exception is thrown, the * counter <code>written</code> is incremented by <code>2</code>. * * @param v a <code>char</code> value to be written. * @exception IOException if an I/O error occurs. * @see java.io.FilterOutputStream#out */ public final void writeChar(int v) throws IOException { out.write((v >>> 8) & 0xFF); out.write((v >>> 0) & 0xFF); incCount(2); } /** * Writes an <code>int</code> to the underlying output stream as four * bytes, high byte first. If no exception is thrown, the counter * <code>written</code> is incremented by <code>4</code>. * * @param v an <code>int</code> to be written. * @exception IOException if an I/O error occurs. * @see java.io.FilterOutputStream#out */ public final void writeInt(int v) throws IOException { out.write((v >>> 24) & 0xFF); out.write((v >>> 16) & 0xFF); out.write((v >>> 8) & 0xFF); out.write((v >>> 0) & 0xFF); incCount(4); } private byte writeBuffer[] = new byte[8]; /** * Writes a <code>long</code> to the underlying output stream as eight * bytes, high byte first. In no exception is thrown, the counter * <code>written</code> is incremented by <code>8</code>. * * @param v a <code>long</code> to be written. * @exception IOException if an I/O error occurs. * @see java.io.FilterOutputStream#out */ public final void writeLong(long v) throws IOException { writeBuffer[0] = (byte) (v >>> 56); writeBuffer[1] = (byte) (v >>> 48); writeBuffer[2] = (byte) (v >>> 40); writeBuffer[3] = (byte) (v >>> 32); writeBuffer[4] = (byte) (v >>> 24); writeBuffer[5] = (byte) (v >>> 16); writeBuffer[6] = (byte) (v >>> 8); writeBuffer[7] = (byte) (v >>> 0); out.write(writeBuffer, 0, 8); incCount(8); } /** * Converts the float argument to an <code>int</code> using the * <code>floatToIntBits</code> method in class <code>Float</code>, * and then writes that <code>int</code> value to the underlying * output stream as a 4-byte quantity, high byte first. If no * exception is thrown, the counter <code>written</code> is * incremented by <code>4</code>. * * @param v a <code>float</code> value to be written. * @exception IOException if an I/O error occurs. * @see java.io.FilterOutputStream#out * @see java.lang.Float#floatToIntBits(float) */ public final void writeFloat(float v) throws IOException { writeInt(Float.floatToIntBits(v)); } /** * Converts the double argument to a <code>long</code> using the * <code>doubleToLongBits</code> method in class <code>Double</code>, * and then writes that <code>long</code> value to the underlying * output stream as an 8-byte quantity, high byte first. If no * exception is thrown, the counter <code>written</code> is * incremented by <code>8</code>. * * @param v a <code>double</code> value to be written. * @exception IOException if an I/O error occurs. * @see java.io.FilterOutputStream#out * @see java.lang.Double#doubleToLongBits(double) */ public final void writeDouble(double v) throws IOException { writeLong(Double.doubleToLongBits(v)); } /** * Writes out the string to the underlying output stream as a * sequence of bytes. Each character in the string is written out, in * sequence, by discarding its high eight bits. If no exception is * thrown, the counter <code>written</code> is incremented by the * length of <code>s</code>. * * @param s a string of bytes to be written. * @exception IOException if an I/O error occurs. * @see java.io.FilterOutputStream#out */ public final void writeBytes(String s) throws IOException { int len = s.length(); for (int i = 0; i < len; i++) { out.write((byte) s.charAt(i)); } incCount(len); } /** * Writes a string to the underlying output stream as a sequence of * characters. Each character is written to the data output stream as * if by the <code>writeChar</code> method. If no exception is * thrown, the counter <code>written</code> is incremented by twice * the length of <code>s</code>. * * @param s a <code>String</code> value to be written. * @exception IOException if an I/O error occurs. * @see java.io.DataOutputStream#writeChar(int) * @see java.io.FilterOutputStream#out */ public final void writeChars(String s) throws IOException { int len = s.length(); for (int i = 0; i < len; i++) { int v = s.charAt(i); out.write((v >>> 8) & 0xFF); out.write((v >>> 0) & 0xFF); } incCount(len * 2); } /** * Writes a string to the underlying output stream using * <a href="DataInput.html#modified-utf-8">modified UTF-8</a> * encoding in a machine-independent manner. * <p> * First, two bytes are written to the output stream as if by the * <code>writeShort</code> method giving the number of bytes to * follow. This value is the number of bytes actually written out, * not the length of the string. Following the length, each character * of the string is output, in sequence, using the modified UTF-8 encoding * for the character. If no exception is thrown, the counter * <code>written</code> is incremented by the total number of * bytes written to the output stream. This will be at least two * plus the length of <code>str</code>, and at most two plus * thrice the length of <code>str</code>. * * @param str a string to be written. * @throws UTFDataFormatException if the modified UTF-8 encoding of * {@code str} would exceed 65535 bytes in length * @throws IOException if some other I/O error occurs. * @see #writeChars(String) */ public final void writeUTF(String str) throws IOException { writeUTF(str, this); } /** * Writes a string to the specified DataOutput using * <a href="DataInput.html#modified-utf-8">modified UTF-8</a> * encoding in a machine-independent manner. * <p> * First, two bytes are written to out as if by the <code>writeShort</code> * method giving the number of bytes to follow. This value is the number of * bytes actually written out, not the length of the string. Following the * length, each character of the string is output, in sequence, using the * modified UTF-8 encoding for the character. If no exception is thrown, the * counter <code>written</code> is incremented by the total number of * bytes written to the output stream. This will be at least two * plus the length of <code>str</code>, and at most two plus * thrice the length of <code>str</code>. * * @param str a string to be written. * @param out destination to write to * @return The number of bytes written out. * @throws UTFDataFormatException if the modified UTF-8 encoding of * {@code str} would exceed 65535 bytes in length * @throws IOException if some other I/O error occurs. */ static int writeUTF(String str, DataOutput out) throws IOException { final int strlen = str.length(); int utflen = strlen; // optimized for ASCII for (int i = 0; i < strlen; i++) { int c = str.charAt(i); if (c >= 0x80 || c == 0) utflen += (c >= 0x800) ? 2 : 1; } if (utflen > 65535 || /* overflow */ utflen < strlen) throw new UTFDataFormatException(tooLongMsg(str, utflen)); final byte[] bytearr; if (out instanceof DataOutputStream) { DataOutputStream dos = (DataOutputStream) out; if (dos.bytearr == null || (dos.bytearr.length < (utflen + 2))) dos.bytearr = new byte[(utflen * 2) + 2]; bytearr = dos.bytearr; } else { bytearr = new byte[utflen + 2]; } int count = 0; bytearr[count++] = (byte) ((utflen >>> 8) & 0xFF); bytearr[count++] = (byte) ((utflen >>> 0) & 0xFF); int i = 0; for (i = 0; i < strlen; i++) { // optimized for initial run of ASCII int c = str.charAt(i); if (c >= 0x80 || c == 0) break; bytearr[count++] = (byte) c; } for (; i < strlen; i++) { int c = str.charAt(i); if (c < 0x80 && c != 0) { bytearr[count++] = (byte) c; } else if (c >= 0x800) { bytearr[count++] = (byte) (0xE0 | ((c >> 12) & 0x0F)); bytearr[count++] = (byte) (0x80 | ((c >> 6) & 0x3F)); bytearr[count++] = (byte) (0x80 | ((c >> 0) & 0x3F)); } else { bytearr[count++] = (byte) (0xC0 | ((c >> 6) & 0x1F)); bytearr[count++] = (byte) (0x80 | ((c >> 0) & 0x3F)); } } out.write(bytearr, 0, utflen + 2); return utflen + 2; } private static String tooLongMsg(String s, int bits32) { int slen = s.length(); String head = s.substring(0, 8); String tail = s.substring(slen - 8, slen); // handle int overflow with max 3x expansion long actualLength = (long) slen + Integer.toUnsignedLong(bits32 - slen); return "encoded string (" + head + "..." + tail + ") too long: " + actualLength + " bytes"; } /** * Returns the current value of the counter <code>written</code>, * the number of bytes written to this data output stream so far. * If the counter overflows, it will be wrapped to Integer.MAX_VALUE. * * @return the value of the <code>written</code> field. * @see java.io.DataOutputStream#written */ public final int size() { return written; } }