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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* accompanied this code).
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package java.io;
This abstract class is the superclass of all classes representing
an input stream of bytes.
Applications that need to define a subclass of InputStream
must always provide a method that returns the next byte of input.
Author: Arthur van Hoff See Also: Since: JDK1.0
/**
* This abstract class is the superclass of all classes representing
* an input stream of bytes.
*
* <p> Applications that need to define a subclass of <code>InputStream</code>
* must always provide a method that returns the next byte of input.
*
* @author Arthur van Hoff
* @see java.io.BufferedInputStream
* @see java.io.ByteArrayInputStream
* @see java.io.DataInputStream
* @see java.io.FilterInputStream
* @see java.io.InputStream#read()
* @see java.io.OutputStream
* @see java.io.PushbackInputStream
* @since JDK1.0
*/
public abstract class InputStream implements Closeable {
// MAX_SKIP_BUFFER_SIZE is used to determine the maximum buffer size to
// use when skipping.
private static final int MAX_SKIP_BUFFER_SIZE = 2048;
Reads the next byte of data from the input stream. The value byte is
returned as an int in the range 0 to
255. If no byte is available because the end of the stream
has been reached, the value -1 is returned. This method
blocks until input data is available, the end of the stream is detected,
or an exception is thrown.
A subclass must provide an implementation of this method.
Throws: - IOException – if an I/O error occurs.
Returns: the next byte of data, or -1 if the end of the
stream is reached.
/**
* Reads the next byte of data from the input stream. The value byte is
* returned as an <code>int</code> in the range <code>0</code> to
* <code>255</code>. If no byte is available because the end of the stream
* has been reached, the value <code>-1</code> is returned. This method
* blocks until input data is available, the end of the stream is detected,
* or an exception is thrown.
*
* <p> A subclass must provide an implementation of this method.
*
* @return the next byte of data, or <code>-1</code> if the end of the
* stream is reached.
* @exception IOException if an I/O error occurs.
*/
public abstract int read() throws IOException;
Reads some number of bytes from the input stream and stores them into
the buffer array 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.
If the length of b is zero, then no bytes are read and
0 is returned; otherwise, there is an attempt to read at
least one byte. If no byte is available because the stream is at the
end of the file, the value -1 is returned; otherwise, at
least one byte is read and stored into b.
The first byte read is stored into element b[0], the
next one into b[1], and so on. The number of bytes read is,
at most, equal to the length of b. Let k be the
number of bytes actually read; these bytes will be stored in elements
b[0] through b[k-1],
leaving elements b[k] through
b[b.length-1] unaffected.
The read(b) method for class InputStream
has the same effect as:
read(b, 0, b.length)
Params: - b – the buffer into which the data is read.
Throws: - IOException – If the first byte cannot be read for any reason
other than the end of the file, if the input stream has been closed, or
if some other I/O error occurs.
- NullPointerException – if
b is null.
See Also: Returns: the total number of bytes read into the buffer, or
-1 if there is no more data because the end of
the stream has been reached.
/**
* Reads some number of bytes from the 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 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 the
* end of the 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 <i>k</i> be the
* number of bytes actually read; these bytes will be stored in elements
* <code>b[0]</code> through <code>b[</code><i>k</i><code>-1]</code>,
* leaving elements <code>b[</code><i>k</i><code>]</code> through
* <code>b[b.length-1]</code> unaffected.
*
* <p> The <code>read(b)</code> method for class <code>InputStream</code>
* has the same effect as: <pre><code> read(b, 0, b.length) </code></pre>
*
* @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 the end of the file, if the input stream has been closed, or
* if some other I/O error occurs.
* @exception NullPointerException if <code>b</code> is <code>null</code>.
* @see java.io.InputStream#read(byte[], int, int)
*/
public int read(byte b[]) throws IOException {
return read(b, 0, b.length);
}
Reads up to len bytes of data from the input stream into
an array of bytes. An attempt is made to read as many as
len bytes, but a smaller number may be read.
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.
If len is zero, then no bytes are read and
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 -1 is returned; otherwise, at least one
byte is read and stored into b.
The first byte read is stored into element b[off], the
next one into b[off+1], and so on. The number of bytes read
is, at most, equal to len. Let k be the number of
bytes actually read; these bytes will be stored in elements
b[off] through b[off+k-1],
leaving elements b[off+k] through
b[off+len-1] unaffected.
In every case, elements b[0] through
b[off] and elements b[off+len] through
b[b.length-1] are unaffected.
The read(b, off, len) method
for class InputStream simply calls the method
read() repeatedly. If the first such call results in an
IOException, that exception is returned from the call to
the read(b, off, len) method. If
any subsequent call to read() results in a
IOException, the exception is caught and treated as if it
were end of file; the bytes read up to that point are stored into
b and the number of bytes read before the exception
occurred is returned. The default implementation of this method blocks
until the requested amount of input data len has been read,
end of file is detected, or an exception is thrown. Subclasses are encouraged
to provide a more efficient implementation of this method.
Params: - b – the buffer into which the data is read.
- off – the start offset in array
b
at which the data is written. - len – the maximum number of bytes to read.
Throws: - IOException – If the first byte cannot be read for any reason
other than end of file, or if the input stream has been closed, or if
some other I/O error occurs.
- NullPointerException – If
b is null. - IndexOutOfBoundsException – If
off is negative,
len is negative, or len is greater than
b.length - off
See Also: Returns: the total number of bytes read into the buffer, or
-1 if there is no more data because the end of
the stream has been reached.
/**
* Reads up to <code>len</code> bytes of data from the 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.
* 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.
*
* <p> The <code>read(b,</code> <code>off,</code> <code>len)</code> method
* for class <code>InputStream</code> simply calls the method
* <code>read()</code> repeatedly. If the first such call results in an
* <code>IOException</code>, that exception is returned from the call to
* the <code>read(b,</code> <code>off,</code> <code>len)</code> method. If
* any subsequent call to <code>read()</code> results in a
* <code>IOException</code>, the exception is caught and treated as if it
* were end of file; the bytes read up to that point are stored into
* <code>b</code> and the number of bytes read before the exception
* occurred is returned. The default implementation of this method blocks
* until the requested amount of input data <code>len</code> has been read,
* end of file is detected, or an exception is thrown. Subclasses are encouraged
* to provide a more efficient implementation of this method.
*
* @param b the buffer into which the data is read.
* @param off the start offset in array <code>b</code>
* at which the data is written.
* @param len the maximum number of bytes to 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, or if the input stream has been closed, or if
* some other I/O error occurs.
* @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>
* @see java.io.InputStream#read()
*/
public int read(byte b[], int off, int len) throws IOException {
if (b == null) {
throw new NullPointerException();
} else if (off < 0 || len < 0 || len > b.length - off) {
throw new IndexOutOfBoundsException();
} else if (len == 0) {
return 0;
}
int c = read();
if (c == -1) {
return -1;
}
b[off] = (byte)c;
int i = 1;
try {
for (; i < len ; i++) {
c = read();
if (c == -1) {
break;
}
b[off + i] = (byte)c;
}
} catch (IOException ee) {
}
return i;
}
Skips over and discards n bytes of data from this input
stream. The skip method may, for a variety of reasons, end
up skipping over some smaller number of bytes, possibly 0.
This may result from any of a number of conditions; reaching end of file
before n bytes have been skipped is only one possibility. The actual number of bytes skipped is returned. If n is negative, the skip method for class InputStream always returns 0, and no bytes are skipped. Subclasses may handle the negative value differently. The skip method of this class creates a
byte array and then repeatedly reads into it until n bytes
have been read or the end of the stream has been reached. Subclasses are
encouraged to provide a more efficient implementation of this method.
For instance, the implementation may depend on the ability to seek.
Params: - n – the number of bytes to be skipped.
Throws: - IOException – if the stream does not support seek,
or if some other I/O error occurs.
Returns: the actual number of bytes skipped.
/**
* Skips over and discards <code>n</code> bytes of data from this input
* stream. The <code>skip</code> method may, for a variety of reasons, end
* up skipping over some smaller number of bytes, possibly <code>0</code>.
* This may result from any of a number of conditions; reaching end of file
* before <code>n</code> bytes have been skipped is only one possibility.
* The actual number of bytes skipped is returned. If {@code n} is
* negative, the {@code skip} method for class {@code InputStream} always
* returns 0, and no bytes are skipped. Subclasses may handle the negative
* value differently.
*
* <p> The <code>skip</code> method of this class creates a
* byte array and then repeatedly reads into it until <code>n</code> bytes
* have been read or the end of the stream has been reached. Subclasses are
* encouraged to provide a more efficient implementation of this method.
* For instance, the implementation may depend on the ability to seek.
*
* @param n the number of bytes to be skipped.
* @return the actual number of bytes skipped.
* @exception IOException if the stream does not support seek,
* or if some other I/O error occurs.
*/
public long skip(long n) throws IOException {
long remaining = n;
int nr;
if (n <= 0) {
return 0;
}
int size = (int)Math.min(MAX_SKIP_BUFFER_SIZE, remaining);
byte[] skipBuffer = new byte[size];
while (remaining > 0) {
nr = read(skipBuffer, 0, (int)Math.min(size, remaining));
if (nr < 0) {
break;
}
remaining -= nr;
}
return n - remaining;
}
Returns an estimate of the number of bytes that can be read (or
skipped over) from this input stream without blocking by the next
invocation of a method for this input stream. The next invocation
might be the same thread or another thread. A single read or skip of this
many bytes will not block, but may read or skip fewer bytes.
Note that while some implementations of InputStream will return the total number of bytes in the stream, many will not. It is never correct to use the return value of this method to allocate a buffer intended to hold all data in this stream.
A subclass' implementation of this method may choose to throw an IOException if this input stream has been closed by invoking the close() method.
The available method for class InputStream always returns 0.
This method should be overridden by subclasses.
Throws: - IOException – if an I/O error occurs.
Returns: an estimate of the number of bytes that can be read (or skipped over) from this input stream without blocking or 0 when it reaches the end of the input stream.
/**
* Returns an estimate of the number of bytes that can be read (or
* skipped over) from this input stream without blocking by the next
* invocation of a method for this input stream. The next invocation
* might be the same thread or another thread. A single read or skip of this
* many bytes will not block, but may read or skip fewer bytes.
*
* <p> Note that while some implementations of {@code InputStream} will return
* the total number of bytes in the stream, many will not. It is
* never correct to use the return value of this method to allocate
* a buffer intended to hold all data in this stream.
*
* <p> A subclass' implementation of this method may choose to throw an
* {@link IOException} if this input stream has been closed by
* invoking the {@link #close()} method.
*
* <p> The {@code available} method for class {@code InputStream} always
* returns {@code 0}.
*
* <p> This method should be overridden by subclasses.
*
* @return an estimate of the number of bytes that can be read (or skipped
* over) from this input stream without blocking or {@code 0} when
* it reaches the end of the input stream.
* @exception IOException if an I/O error occurs.
*/
public int available() throws IOException {
return 0;
}
Closes this input stream and releases any system resources associated
with the stream.
The close method of InputStream does
nothing.
Throws: - IOException – if an I/O error occurs.
/**
* Closes this input stream and releases any system resources associated
* with the stream.
*
* <p> The <code>close</code> method of <code>InputStream</code> does
* nothing.
*
* @exception IOException if an I/O error occurs.
*/
public void close() throws IOException {}
Marks the current position in this input stream. A subsequent call to
the reset method repositions this stream at the last marked
position so that subsequent reads re-read the same bytes.
The readlimit arguments tells this input stream to
allow that many bytes to be read before the mark position gets
invalidated.
The general contract of mark is that, if the method
markSupported returns true, the stream somehow
remembers all the bytes read after the call to mark and
stands ready to supply those same bytes again if and whenever the method
reset is called. However, the stream is not required to
remember any data at all if more than readlimit bytes are
read from the stream before reset is called.
Marking a closed stream should not have any effect on the stream.
The mark method of InputStream does
nothing.
Params: - readlimit – the maximum limit of bytes that can be read before
the mark position becomes invalid.
See Also:
/**
* Marks the current position in this input stream. A subsequent call to
* the <code>reset</code> method repositions this stream at the last marked
* position so that subsequent reads re-read the same bytes.
*
* <p> The <code>readlimit</code> arguments tells this input stream to
* allow that many bytes to be read before the mark position gets
* invalidated.
*
* <p> The general contract of <code>mark</code> is that, if the method
* <code>markSupported</code> returns <code>true</code>, the stream somehow
* remembers all the bytes read after the call to <code>mark</code> and
* stands ready to supply those same bytes again if and whenever the method
* <code>reset</code> is called. However, the stream is not required to
* remember any data at all if more than <code>readlimit</code> bytes are
* read from the stream before <code>reset</code> is called.
*
* <p> Marking a closed stream should not have any effect on the stream.
*
* <p> The <code>mark</code> method of <code>InputStream</code> does
* nothing.
*
* @param readlimit the maximum limit of bytes that can be read before
* the mark position becomes invalid.
* @see java.io.InputStream#reset()
*/
public synchronized void mark(int readlimit) {}
Repositions this stream to the position at the time the
mark method was last called on this input stream.
The general contract of reset is:
- If the method
markSupported returns
true, then:
- If the method
mark has not been called since
the stream was created, or the number of bytes read from the stream
since mark was last called is larger than the argument
to mark at that last call, then an
IOException might be thrown.
- If such an
IOException is not thrown, then the
stream is reset to a state such that all the bytes read since the
most recent call to mark (or since the start of the
file, if mark has not been called) will be resupplied
to subsequent callers of the read method, followed by
any bytes that otherwise would have been the next input data as of
the time of the call to reset.
- If the method
markSupported returns
false, then:
- The call to
reset may throw an
IOException.
- If an
IOException is not thrown, then the stream
is reset to a fixed state that depends on the particular type of the
input stream and how it was created. The bytes that will be supplied
to subsequent callers of the read method depend on the
particular type of the input stream.
The method reset for class InputStream
does nothing except throw an IOException.
Throws: - IOException – if this stream has not been marked or if the
mark has been invalidated.
See Also:
/**
* Repositions this stream to the position at the time the
* <code>mark</code> method was last called on this input stream.
*
* <p> The general contract of <code>reset</code> is:
*
* <ul>
* <li> If the method <code>markSupported</code> returns
* <code>true</code>, then:
*
* <ul><li> If the method <code>mark</code> has not been called since
* the stream was created, or the number of bytes read from the stream
* since <code>mark</code> was last called is larger than the argument
* to <code>mark</code> at that last call, then an
* <code>IOException</code> might be thrown.
*
* <li> If such an <code>IOException</code> is not thrown, then the
* stream is reset to a state such that all the bytes read since the
* most recent call to <code>mark</code> (or since the start of the
* file, if <code>mark</code> has not been called) will be resupplied
* to subsequent callers of the <code>read</code> method, followed by
* any bytes that otherwise would have been the next input data as of
* the time of the call to <code>reset</code>. </ul>
*
* <li> If the method <code>markSupported</code> returns
* <code>false</code>, then:
*
* <ul><li> The call to <code>reset</code> may throw an
* <code>IOException</code>.
*
* <li> If an <code>IOException</code> is not thrown, then the stream
* is reset to a fixed state that depends on the particular type of the
* input stream and how it was created. The bytes that will be supplied
* to subsequent callers of the <code>read</code> method depend on the
* particular type of the input stream. </ul></ul>
*
* <p>The method <code>reset</code> for class <code>InputStream</code>
* does nothing except throw an <code>IOException</code>.
*
* @exception IOException if this stream has not been marked or if the
* mark has been invalidated.
* @see java.io.InputStream#mark(int)
* @see java.io.IOException
*/
public synchronized void reset() throws IOException {
throw new IOException("mark/reset not supported");
}
Tests if this input stream supports the mark and
reset methods. Whether or not mark and
reset are supported is an invariant property of a
particular input stream instance. The markSupported method
of InputStream returns false.
See Also: Returns: true if this stream instance supports the mark
and reset methods; false otherwise.
/**
* Tests if this input stream supports the <code>mark</code> and
* <code>reset</code> methods. Whether or not <code>mark</code> and
* <code>reset</code> are supported is an invariant property of a
* particular input stream instance. The <code>markSupported</code> method
* of <code>InputStream</code> returns <code>false</code>.
*
* @return <code>true</code> if this stream instance supports the mark
* and reset methods; <code>false</code> otherwise.
* @see java.io.InputStream#mark(int)
* @see java.io.InputStream#reset()
*/
public boolean markSupported() {
return false;
}
}