The DataInputStream.java Java example source code
/*
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* 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
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*/
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 JDK1.0
*/
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. 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 b is null, a NullPointerException is
* thrown. If the length of <code>b is zero, then no bytes are
* read and <code>0 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 is returned;
* otherwise, at least one byte is read and stored into <code>b.
*
* <p>The first byte read is stored into element b[0], the
* next one into <code>b[1], and so on. The number of bytes read
* is, at most, equal to the length of <code>b. Let k
* be the number of bytes actually read; these bytes will be stored in
* elements <code>b[0] through b[k-1], leaving
* elements <code>b[k] through b[b.length-1]
* unaffected.
*
* <p>The read(b) method has the same effect as:
* <blockquote> * read(b, 0, b.length)
* </pre>
*
* @param b the buffer into which the data is read.
* @return the total number of bytes read into the buffer, or
* <code>-1 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 bytes of data from the contained
* input stream into an array of bytes. An attempt is made to read
* as many as <code>len 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 len is zero, then no bytes are read and
* <code>0 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 is returned; otherwise, at least one
* byte is read and stored into <code>b.
*
* <p> The first byte read is stored into element b[off], the
* next one into <code>b[off+1], and so on. The number of bytes read
* is, at most, equal to <code>len. Let k be the number of
* bytes actually read; these bytes will be stored in elements
* <code>b[off] through b[off+k-1],
* leaving elements <code>b[off+k] through
* <code>b[off+len-1] unaffected.
*
* <p> In every case, elements b[0] through
* <code>b[off] and elements b[off+len] through
* <code>b[b.length-1] are unaffected.
*
* @param b the buffer into which the data is read.
* @param off the start offset in the destination array <code>b
* @param len the maximum number of bytes read.
* @return the total number of bytes read into the buffer, or
* <code>-1 if there is no more data because the end
* of the stream has been reached.
* @exception NullPointerException If <code>b is null.
* @exception IndexOutOfBoundsException If <code>off is negative,
* <code>len is negative, or len is greater than
* <code>b.length - off
* @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.
* @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[]) 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 of the data.
* @param len the number of bytes to read.
* @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
* method of <code>DataInput.
* <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
* method of <code>DataInput.
* <p>
* Bytes for this operation are read from the contained
* input stream.
*
* @return the <code>boolean 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
* method of <code>DataInput.
* <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.
* @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
* method of <code>DataInput.
* <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
* method of <code>DataInput.
* <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
* method of <code>DataInput.
* <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
* method of <code>DataInput.
* <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.
* @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
* method of <code>DataInput.
* <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.
* @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
* method of <code>DataInput.
* <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.
* @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
* method of <code>DataInput.
* <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.
* @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
* method of <code>DataInput.
* <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.
* @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
* method of <code>DataInput.
* <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() method. Programs that use the
* <code>DataInputStream class to read lines can be converted to use
* the <code>BufferedReader class by replacing code of the form:
* <blockquote> * DataInputStream d = new DataInputStream(in);
* </pre>
* with:
* <blockquote> * BufferedReader d
* = new BufferedReader(new InputStreamReader(in));
* </pre>
*
* @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
* method of <code>DataInput.
* <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 a representation
* of a Unicode character string encoded in
* <a href="DataInput.html#modified-utf-8">modified UTF-8 format;
* this string of characters is then returned as a <code>String.
* The details of the modified UTF-8 representation
* are exactly the same as for the <code>readUTF
* method of <code>DataInput.
*
* @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 final static 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);
}
}
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