public abstract class InputStream extends Object implements Closeable
Most clients will use input streams that read data from the file system
(FileInputStream), the network (Socket.getInputStream()/URLConnection.getInputStream()), or from an in-memory byte
array (ByteArrayInputStream).
Use InputStreamReader to adapt a byte stream like this one into a
character stream.
Most clients should wrap their input stream with BufferedInputStream. Callers that do only bulk reads may omit buffering.
Some implementations support marking a position in the input stream and
resetting back to this position later. Implementations that don't return
false from markSupported() and throw an IOException when
reset() is called.
FilterInputStream, which delegates all calls to the source input
stream.
All input stream subclasses should override both read() and read(byte[],int,int). The
three argument overload is necessary for bulk access to the data. This is
much more efficient than byte-by-byte access.
OutputStream| Constructor and Description |
|---|
InputStream()
This constructor does nothing.
|
| Modifier and Type | Method and Description |
|---|---|
int |
available()
Returns an estimated number of bytes that can be read or skipped without blocking for more
input.
|
void |
close()
Closes this stream.
|
void |
mark(int readlimit)
Sets a mark position in this InputStream.
|
boolean |
markSupported()
Indicates whether this stream supports the
mark() and
reset() methods. |
abstract int |
read()
Reads a single byte from this stream and returns it as an integer in the
range from 0 to 255.
|
int |
read(byte[] buffer)
Equivalent to
read(buffer, 0, buffer.length). |
int |
read(byte[] buffer,
int offset,
int length)
Reads at most
length bytes from this stream and stores them in
the byte array b starting at offset. |
void |
reset()
Resets this stream to the last marked location.
|
long |
skip(long byteCount)
Skips at most
n bytes in this stream. |
public InputStream()
public int available()
throws IOException
Note that this method provides such a weak guarantee that it is not very useful in practice.
Firstly, the guarantee is "without blocking for more input" rather than "without blocking": a read may still block waiting for I/O to complete — the guarantee is merely that it won't have to wait indefinitely for data to be written. The result of this method should not be used as a license to do I/O on a thread that shouldn't be blocked.
Secondly, the result is a conservative estimate and may be significantly smaller than the actual number of bytes available. In particular, an implementation that always returns 0 would be correct. In general, callers should only use this method if they'd be satisfied with treating the result as a boolean yes or no answer to the question "is there definitely data ready?".
Thirdly, the fact that a given number of bytes is "available" does not guarantee that a read or skip will actually read or skip that many bytes: they may read or skip fewer.
It is particularly important to realize that you must not use this method to
size a container and assume that you can read the entirety of the stream without needing
to resize the container. Such callers should probably write everything they read to a
ByteArrayOutputStream and convert that to a byte array. Alternatively, if you're
reading from a file, File.length() returns the current length of the file (though
assuming the file's length can't change may be incorrect, reading a file is inherently
racy).
The default implementation of this method in InputStream always returns 0.
Subclasses should override this method if they are able to indicate the number of bytes
available.
IOException - if this stream is closed or an error occurspublic void close()
throws IOException
close in interface Closeableclose in interface AutoCloseableIOException - if an error occurs while closing this stream.public void mark(int readlimit)
readlimit
indicates how many bytes can be read before the mark is invalidated.
Sending reset() will reposition the stream back to the marked
position provided readLimit has not been surpassed.
This default implementation does nothing and concrete subclasses must provide their own implementation.
readlimit - the number of bytes that can be read from this stream before
the mark is invalidated.markSupported(),
reset()public boolean markSupported()
mark() and
reset() methods. The default implementation returns false.public abstract int read()
throws IOException
IOException - if the stream is closed or another IOException occurs.public int read(byte[] buffer)
throws IOException
read(buffer, 0, buffer.length).IOExceptionpublic int read(byte[] buffer,
int offset,
int length)
throws IOException
length bytes from this stream and stores them in
the byte array b starting at offset.buffer - the byte array in which to store the bytes read.offset - the initial position in buffer to store the bytes read
from this stream.length - the maximum number of bytes to store in b.IndexOutOfBoundsException - if offset < 0 or length < 0, or if
offset + length is greater than the length of
b.IOException - if the stream is closed or another IOException occurs.public void reset()
throws IOException
IOException if the number of bytes read since the mark has been
set is greater than the limit provided to mark, or if no mark
has been set.
This implementation always throws an IOException and concrete
subclasses should provide the proper implementation.
IOException - if this stream is closed or another IOException occurs.public long skip(long byteCount)
throws IOException
n bytes in this stream. This method does nothing and returns
0 if n is negative, but some subclasses may throw.
Note the "at most" in the description of this method: this method may choose to skip fewer bytes than requested. Callers should always check the return value.
This default implementation reads bytes into a temporary buffer. Concrete subclasses should provide their own implementation.
byteCount - the number of bytes to skip.IOException - if this stream is closed or another IOException occurs.