Java tutorial
/* * Copyright (c) 1994, 2016, 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 input stream lets an application read primitive Java data * types from an underlying input stream in a machine-independent * way. An application uses a data output stream to write data that * can later be read by a data input stream. * <p> * DataInputStream is not necessarily safe for multithreaded access. * Thread safety is optional and is the responsibility of users of * methods in this class. * * @author Arthur van Hoff * @see java.io.DataOutputStream * @since 1.0 */ public class DataInputStream extends FilterInputStream implements DataInput { /** * Creates a DataInputStream that uses the specified * underlying InputStream. * * @param in the specified input stream */ public DataInputStream(InputStream in) { super(in); } /** * working arrays initialized on demand by readUTF */ private byte bytearr[] = new byte[80]; private char chararr[] = new char[80]; /** * Reads some number of bytes from the contained input stream and * stores them into the buffer array <code>b</code>. The number of * bytes actually read is returned as an integer. This method blocks * until input data is available, end of file is detected, or an * exception is thrown. * * <p>If <code>b</code> is null, a <code>NullPointerException</code> is * thrown. If the length of <code>b</code> is zero, then no bytes are * read and <code>0</code> is returned; otherwise, there is an attempt * to read at least one byte. If no byte is available because the * stream is at end of file, the value <code>-1</code> is returned; * otherwise, at least one byte is read and stored into <code>b</code>. * * <p>The first byte read is stored into element <code>b[0]</code>, the * next one into <code>b[1]</code>, and so on. The number of bytes read * is, at most, equal to the length of <code>b</code>. Let <code>k</code> * be the number of bytes actually read; these bytes will be stored in * elements <code>b[0]</code> through <code>b[k-1]</code>, leaving * elements <code>b[k]</code> through <code>b[b.length-1]</code> * unaffected. * * <p>The <code>read(b)</code> method has the same effect as: * <blockquote><pre> * read(b, 0, b.length) * </pre></blockquote> * * @param b the buffer into which the data is read. * @return the total number of bytes read into the buffer, or * <code>-1</code> if there is no more data because the end * of the stream has been reached. * @exception IOException if the first byte cannot be read for any reason * other than end of file, the stream has been closed and the underlying * input stream does not support reading after close, or another I/O * error occurs. * @see java.io.FilterInputStream#in * @see java.io.InputStream#read(byte[], int, int) */ public final int read(byte b[]) throws IOException { return in.read(b, 0, b.length); } /** * Reads up to <code>len</code> bytes of data from the contained * input stream into an array of bytes. An attempt is made to read * as many as <code>len</code> bytes, but a smaller number may be read, * possibly zero. The number of bytes actually read is returned as an * integer. * * <p> This method blocks until input data is available, end of file is * detected, or an exception is thrown. * * <p> If <code>len</code> is zero, then no bytes are read and * <code>0</code> is returned; otherwise, there is an attempt to read at * least one byte. If no byte is available because the stream is at end of * file, the value <code>-1</code> is returned; otherwise, at least one * byte is read and stored into <code>b</code>. * * <p> The first byte read is stored into element <code>b[off]</code>, the * next one into <code>b[off+1]</code>, and so on. The number of bytes read * is, at most, equal to <code>len</code>. Let <i>k</i> be the number of * bytes actually read; these bytes will be stored in elements * <code>b[off]</code> through <code>b[off+</code><i>k</i><code>-1]</code>, * leaving elements <code>b[off+</code><i>k</i><code>]</code> through * <code>b[off+len-1]</code> unaffected. * * <p> In every case, elements <code>b[0]</code> through * <code>b[off]</code> and elements <code>b[off+len]</code> through * <code>b[b.length-1]</code> are unaffected. * * @param b the buffer into which the data is read. * @param off the start offset in the destination array <code>b</code> * @param len the maximum number of bytes read. * @return the total number of bytes read into the buffer, or * <code>-1</code> if there is no more data because the end * of the stream has been reached. * @exception NullPointerException If <code>b</code> is <code>null</code>. * @exception IndexOutOfBoundsException If <code>off</code> is negative, * <code>len</code> is negative, or <code>len</code> is greater than * <code>b.length - off</code> * @exception IOException if the first byte cannot be read for any reason * other than end of file, the stream has been closed and the underlying * input stream does not support reading after close, or another I/O * error occurs. * @see java.io.FilterInputStream#in * @see java.io.InputStream#read(byte[], int, int) */ public final int read(byte b[], int off, int len) throws IOException { return in.read(b, off, len); } /** * See the general contract of the {@code readFully} * method of {@code DataInput}. * <p> * Bytes * for this operation are read from the contained * input stream. * * @param b the buffer into which the data is read. * @throws NullPointerException if {@code b} is {@code null}. * @throws EOFException if this input stream reaches the end before * reading all the bytes. * @throws IOException the stream has been closed and the contained * input stream does not support reading after close, or * another I/O error occurs. * @see java.io.FilterInputStream#in */ public final void readFully(byte b[]) throws IOException { readFully(b, 0, b.length); } /** * See the general contract of the {@code readFully} * method of {@code DataInput}. * <p> * Bytes * for this operation are read from the contained * input stream. * * @param b the buffer into which the data is read. * @param off the start offset in the data array {@code b}. * @param len the number of bytes to read. * @exception NullPointerException if {@code b} is {@code null}. * @exception IndexOutOfBoundsException if {@code off} is negative, * {@code len} is negative, or {@code len} is greater than * {@code b.length - off}. * @exception EOFException if this input stream reaches the end before * reading all the bytes. * @exception IOException the stream has been closed and the contained * input stream does not support reading after close, or * another I/O error occurs. * @see java.io.FilterInputStream#in */ public final void readFully(byte b[], int off, int len) throws IOException { if (len < 0) throw new IndexOutOfBoundsException(); int n = 0; while (n < len) { int count = in.read(b, off + n, len - n); if (count < 0) throw new EOFException(); n += count; } } /** * See the general contract of the <code>skipBytes</code> * method of <code>DataInput</code>. * <p> * Bytes for this operation are read from the contained * input stream. * * @param n the number of bytes to be skipped. * @return the actual number of bytes skipped. * @exception IOException if the contained input stream does not support * seek, or the stream has been closed and * the contained input stream does not support * reading after close, or another I/O error occurs. */ public final int skipBytes(int n) throws IOException { int total = 0; int cur = 0; while ((total < n) && ((cur = (int) in.skip(n - total)) > 0)) { total += cur; } return total; } /** * See the general contract of the <code>readBoolean</code> * method of <code>DataInput</code>. * <p> * Bytes for this operation are read from the contained * input stream. * * @return the <code>boolean</code> value read. * @exception EOFException if this input stream has reached the end. * @exception IOException the stream has been closed and the contained * input stream does not support reading after close, or * another I/O error occurs. * @see java.io.FilterInputStream#in */ public final boolean readBoolean() throws IOException { int ch = in.read(); if (ch < 0) throw new EOFException(); return (ch != 0); } /** * See the general contract of the <code>readByte</code> * method of <code>DataInput</code>. * <p> * Bytes * for this operation are read from the contained * input stream. * * @return the next byte of this input stream as a signed 8-bit * <code>byte</code>. * @exception EOFException if this input stream has reached the end. * @exception IOException the stream has been closed and the contained * input stream does not support reading after close, or * another I/O error occurs. * @see java.io.FilterInputStream#in */ public final byte readByte() throws IOException { int ch = in.read(); if (ch < 0) throw new EOFException(); return (byte) (ch); } /** * See the general contract of the <code>readUnsignedByte</code> * method of <code>DataInput</code>. * <p> * Bytes * for this operation are read from the contained * input stream. * * @return the next byte of this input stream, interpreted as an * unsigned 8-bit number. * @exception EOFException if this input stream has reached the end. * @exception IOException the stream has been closed and the contained * input stream does not support reading after close, or * another I/O error occurs. * @see java.io.FilterInputStream#in */ public final int readUnsignedByte() throws IOException { int ch = in.read(); if (ch < 0) throw new EOFException(); return ch; } /** * See the general contract of the <code>readShort</code> * method of <code>DataInput</code>. * <p> * Bytes * for this operation are read from the contained * input stream. * * @return the next two bytes of this input stream, interpreted as a * signed 16-bit number. * @exception EOFException if this input stream reaches the end before * reading two bytes. * @exception IOException the stream has been closed and the contained * input stream does not support reading after close, or * another I/O error occurs. * @see java.io.FilterInputStream#in */ public final short readShort() throws IOException { int ch1 = in.read(); int ch2 = in.read(); if ((ch1 | ch2) < 0) throw new EOFException(); return (short) ((ch1 << 8) + (ch2 << 0)); } /** * See the general contract of the <code>readUnsignedShort</code> * method of <code>DataInput</code>. * <p> * Bytes * for this operation are read from the contained * input stream. * * @return the next two bytes of this input stream, interpreted as an * unsigned 16-bit integer. * @exception EOFException if this input stream reaches the end before * reading two bytes. * @exception IOException the stream has been closed and the contained * input stream does not support reading after close, or * another I/O error occurs. * @see java.io.FilterInputStream#in */ public final int readUnsignedShort() throws IOException { int ch1 = in.read(); int ch2 = in.read(); if ((ch1 | ch2) < 0) throw new EOFException(); return (ch1 << 8) + (ch2 << 0); } /** * See the general contract of the <code>readChar</code> * method of <code>DataInput</code>. * <p> * Bytes * for this operation are read from the contained * input stream. * * @return the next two bytes of this input stream, interpreted as a * <code>char</code>. * @exception EOFException if this input stream reaches the end before * reading two bytes. * @exception IOException the stream has been closed and the contained * input stream does not support reading after close, or * another I/O error occurs. * @see java.io.FilterInputStream#in */ public final char readChar() throws IOException { int ch1 = in.read(); int ch2 = in.read(); if ((ch1 | ch2) < 0) throw new EOFException(); return (char) ((ch1 << 8) + (ch2 << 0)); } /** * See the general contract of the <code>readInt</code> * method of <code>DataInput</code>. * <p> * Bytes * for this operation are read from the contained * input stream. * * @return the next four bytes of this input stream, interpreted as an * <code>int</code>. * @exception EOFException if this input stream reaches the end before * reading four bytes. * @exception IOException the stream has been closed and the contained * input stream does not support reading after close, or * another I/O error occurs. * @see java.io.FilterInputStream#in */ public final int readInt() throws IOException { int ch1 = in.read(); int ch2 = in.read(); int ch3 = in.read(); int ch4 = in.read(); if ((ch1 | ch2 | ch3 | ch4) < 0) throw new EOFException(); return ((ch1 << 24) + (ch2 << 16) + (ch3 << 8) + (ch4 << 0)); } private byte readBuffer[] = new byte[8]; /** * See the general contract of the <code>readLong</code> * method of <code>DataInput</code>. * <p> * Bytes * for this operation are read from the contained * input stream. * * @return the next eight bytes of this input stream, interpreted as a * <code>long</code>. * @exception EOFException if this input stream reaches the end before * reading eight bytes. * @exception IOException the stream has been closed and the contained * input stream does not support reading after close, or * another I/O error occurs. * @see java.io.FilterInputStream#in */ public final long readLong() throws IOException { readFully(readBuffer, 0, 8); return (((long) readBuffer[0] << 56) + ((long) (readBuffer[1] & 255) << 48) + ((long) (readBuffer[2] & 255) << 40) + ((long) (readBuffer[3] & 255) << 32) + ((long) (readBuffer[4] & 255) << 24) + ((readBuffer[5] & 255) << 16) + ((readBuffer[6] & 255) << 8) + ((readBuffer[7] & 255) << 0)); } /** * See the general contract of the <code>readFloat</code> * method of <code>DataInput</code>. * <p> * Bytes * for this operation are read from the contained * input stream. * * @return the next four bytes of this input stream, interpreted as a * <code>float</code>. * @exception EOFException if this input stream reaches the end before * reading four bytes. * @exception IOException the stream has been closed and the contained * input stream does not support reading after close, or * another I/O error occurs. * @see java.io.DataInputStream#readInt() * @see java.lang.Float#intBitsToFloat(int) */ public final float readFloat() throws IOException { return Float.intBitsToFloat(readInt()); } /** * See the general contract of the <code>readDouble</code> * method of <code>DataInput</code>. * <p> * Bytes * for this operation are read from the contained * input stream. * * @return the next eight bytes of this input stream, interpreted as a * <code>double</code>. * @exception EOFException if this input stream reaches the end before * reading eight bytes. * @exception IOException the stream has been closed and the contained * input stream does not support reading after close, or * another I/O error occurs. * @see java.io.DataInputStream#readLong() * @see java.lang.Double#longBitsToDouble(long) */ public final double readDouble() throws IOException { return Double.longBitsToDouble(readLong()); } private char lineBuffer[]; /** * See the general contract of the <code>readLine</code> * method of <code>DataInput</code>. * <p> * Bytes * for this operation are read from the contained * input stream. * * @deprecated This method does not properly convert bytes to characters. * As of JDK 1.1, the preferred way to read lines of text is via the * <code>BufferedReader.readLine()</code> method. Programs that use the * <code>DataInputStream</code> class to read lines can be converted to use * the <code>BufferedReader</code> class by replacing code of the form: * <blockquote><pre> * DataInputStream d = new DataInputStream(in); * </pre></blockquote> * with: * <blockquote><pre> * BufferedReader d * = new BufferedReader(new InputStreamReader(in)); * </pre></blockquote> * * @return the next line of text from this input stream. * @exception IOException if an I/O error occurs. * @see java.io.BufferedReader#readLine() * @see java.io.FilterInputStream#in */ @Deprecated public final String readLine() throws IOException { char buf[] = lineBuffer; if (buf == null) { buf = lineBuffer = new char[128]; } int room = buf.length; int offset = 0; int c; loop: while (true) { switch (c = in.read()) { case -1: case '\n': break loop; case '\r': int c2 = in.read(); if ((c2 != '\n') && (c2 != -1)) { if (!(in instanceof PushbackInputStream)) { this.in = new PushbackInputStream(in); } ((PushbackInputStream) in).unread(c2); } break loop; default: if (--room < 0) { buf = new char[offset + 128]; room = buf.length - offset - 1; System.arraycopy(lineBuffer, 0, buf, 0, offset); lineBuffer = buf; } buf[offset++] = (char) c; break; } } if ((c == -1) && (offset == 0)) { return null; } return String.copyValueOf(buf, 0, offset); } /** * See the general contract of the <code>readUTF</code> * method of <code>DataInput</code>. * <p> * Bytes * for this operation are read from the contained * input stream. * * @return a Unicode string. * @exception EOFException if this input stream reaches the end before * reading all the bytes. * @exception IOException the stream has been closed and the contained * input stream does not support reading after close, or * another I/O error occurs. * @exception UTFDataFormatException if the bytes do not represent a valid * modified UTF-8 encoding of a string. * @see java.io.DataInputStream#readUTF(java.io.DataInput) */ public final String readUTF() throws IOException { return readUTF(this); } /** * Reads from the * stream <code>in</code> a representation * of a Unicode character string encoded in * <a href="DataInput.html#modified-utf-8">modified UTF-8</a> format; * this string of characters is then returned as a <code>String</code>. * The details of the modified UTF-8 representation * are exactly the same as for the <code>readUTF</code> * method of <code>DataInput</code>. * * @param in a data input stream. * @return a Unicode string. * @exception EOFException if the input stream reaches the end * before all the bytes. * @exception IOException the stream has been closed and the contained * input stream does not support reading after close, or * another I/O error occurs. * @exception UTFDataFormatException if the bytes do not represent a * valid modified UTF-8 encoding of a Unicode string. * @see java.io.DataInputStream#readUnsignedShort() */ public static final String readUTF(DataInput in) throws IOException { int utflen = in.readUnsignedShort(); byte[] bytearr = null; char[] chararr = null; if (in instanceof DataInputStream) { DataInputStream dis = (DataInputStream) in; if (dis.bytearr.length < utflen) { dis.bytearr = new byte[utflen * 2]; dis.chararr = new char[utflen * 2]; } chararr = dis.chararr; bytearr = dis.bytearr; } else { bytearr = new byte[utflen]; chararr = new char[utflen]; } int c, char2, char3; int count = 0; int chararr_count = 0; in.readFully(bytearr, 0, utflen); while (count < utflen) { c = (int) bytearr[count] & 0xff; if (c > 127) break; count++; chararr[chararr_count++] = (char) c; } while (count < utflen) { c = (int) bytearr[count] & 0xff; switch (c >> 4) { case 0: case 1: case 2: case 3: case 4: case 5: case 6: case 7: /* 0xxxxxxx*/ count++; chararr[chararr_count++] = (char) c; break; case 12: case 13: /* 110x xxxx 10xx xxxx*/ count += 2; if (count > utflen) throw new UTFDataFormatException("malformed input: partial character at end"); char2 = (int) bytearr[count - 1]; if ((char2 & 0xC0) != 0x80) throw new UTFDataFormatException("malformed input around byte " + count); chararr[chararr_count++] = (char) (((c & 0x1F) << 6) | (char2 & 0x3F)); break; case 14: /* 1110 xxxx 10xx xxxx 10xx xxxx */ count += 3; if (count > utflen) throw new UTFDataFormatException("malformed input: partial character at end"); char2 = (int) bytearr[count - 2]; char3 = (int) bytearr[count - 1]; if (((char2 & 0xC0) != 0x80) || ((char3 & 0xC0) != 0x80)) throw new UTFDataFormatException("malformed input around byte " + (count - 1)); chararr[chararr_count++] = (char) (((c & 0x0F) << 12) | ((char2 & 0x3F) << 6) | ((char3 & 0x3F) << 0)); break; default: /* 10xx xxxx, 1111 xxxx */ throw new UTFDataFormatException("malformed input around byte " + count); } } // The number of chars produced may be less than utflen return new String(chararr, 0, chararr_count); } }