public abstract classInputStreamextendsObjectimplementsCloseable
Applications that need to define a subclass ofInputStream must always provide a method that returns the next byte of input.
BufferedInputStream,ByteArrayInputStream,DataInputStream,FilterInputStream,read(),OutputStream,PushbackInputStream| Constructor | Description |
|---|---|
InputStream() |
| Modifier and Type | Method | Description |
|---|---|---|
int | available() | 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. |
void | close() | Closes this input stream and releases any system resources associated with the stream. |
void | mark(int readlimit) | Marks the current position in this input stream. |
boolean | markSupported() | Tests if this input stream supports the mark andreset methods. |
abstract int | read() | Reads the next byte of data from the input stream. |
int | read(byte[] b) | Reads some number of bytes from the input stream and stores them into the buffer array b. |
int | read(byte[] b, int off, int len) | Reads up to len bytes of data from the input stream into an array of bytes. |
void | reset() | Repositions this stream to the position at the time the mark method was last called on this input stream. |
long | skip(long n) | Skips over and discards n bytes of data from this input stream. |
public abstract int read() throwsIOException
int in the range0 to255. 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.
-1 if the end of the stream is reached.IOException - if an I/O error occurs.public int read(byte[] b) throwsIOException
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 ofb is zero, then no bytes are read and0 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 intob.
The first byte read is stored into elementb[0], the next one intob[1], and so on. The number of bytes read is, at most, equal to the length ofb. Letk be the number of bytes actually read; these bytes will be stored in elementsb[0] throughb[k-1], leaving elementsb[k] throughb[b.length-1] unaffected.
Theread(b) method for classInputStream has the same effect as:
read(b, 0, b.length)b - the buffer into which the data is read.-1 if there is no more data because the end of the stream has been reached.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 - ifb isnull.read(byte[], int, int)public int read(byte[] b, int off, int len) throwsIOException
len bytes of data from the input stream into an array of bytes. An attempt is made to read as many aslen 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.
Iflen is zero, then no bytes are read and0 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 intob.
The first byte read is stored into elementb[off], the next one intob[off+1], and so on. The number of bytes read is, at most, equal tolen. Letk be the number of bytes actually read; these bytes will be stored in elementsb[off] throughb[off+k-1], leaving elementsb[off+k] throughb[off+len-1] unaffected.
In every case, elementsb[0] throughb[off] and elementsb[off+len] throughb[b.length-1] are unaffected.
Theread(b,off,len) method for classInputStream simply calls the methodread() repeatedly. If the first such call results in anIOException, that exception is returned from the call to theread(b,off,len) method. If any subsequent call toread() results in aIOException, the exception is caught and treated as if it were end of file; the bytes read up to that point are stored intob 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 datalen 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.
b - the buffer into which the data is read.off - the start offset in arrayb at which the data is written.len - the maximum number of bytes to read.-1 if there is no more data because the end of the stream has been reached.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 - Ifb isnull.IndexOutOfBoundsException - Ifoff is negative,len is negative, orlen is greater thanb.length - offread()public long skip(long n) throwsIOException
n bytes of data from this input stream. Theskip method may, for a variety of reasons, end up skipping over some smaller number of bytes, possibly0. This may result from any of a number of conditions; reaching end of file beforen bytes have been skipped is only one possibility. The actual number of bytes skipped is returned. Ifn is negative, theskip method for classInputStream always returns 0, and no bytes are skipped. Subclasses may handle the negative value differently. Theskip method of this class creates a byte array and then repeatedly reads into it untiln 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.
n - the number of bytes to be skipped.IOException - if the stream does not support seek, or if some other I/O error occurs.public int available() throwsIOException
Note that while some implementations ofInputStream 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 anIOException if this input stream has been closed by invoking theclose() method.
Theavailable method for classInputStream always returns0.
This method should be overridden by subclasses.
0 when it reaches the end of the input stream.IOException - if an I/O error occurs.public void close() throwsIOException
Theclose method ofInputStream does nothing.
close in interface Closeableclose in interface AutoCloseableIOException - if an I/O error occurs.public void mark(int readlimit)
reset method repositions this stream at the last marked position so that subsequent reads re-read the same bytes. Thereadlimit arguments tells this input stream to allow that many bytes to be read before the mark position gets invalidated.
The general contract ofmark is that, if the methodmarkSupported returnstrue, the stream somehow remembers all the bytes read after the call tomark and stands ready to supply those same bytes again if and whenever the methodreset is called. However, the stream is not required to remember any data at all if more thanreadlimit bytes are read from the stream beforereset is called.
Marking a closed stream should not have any effect on the stream.
Themark method ofInputStream does nothing.
readlimit - the maximum limit of bytes that can be read before the mark position becomes invalid.reset()public void reset() throwsIOException
mark method was last called on this input stream. The general contract ofreset is:
markSupported returnstrue, then:mark has not been called since the stream was created, or the number of bytes read from the stream sincemark was last called is larger than the argument tomark at that last call, then anIOException might be thrown.IOException is not thrown, then the stream is reset to a state such that all the bytes read since the most recent call tomark (or since the start of the file, ifmark has not been called) will be resupplied to subsequent callers of theread method, followed by any bytes that otherwise would have been the next input data as of the time of the call toreset.markSupported returnsfalse, then:reset may throw anIOException.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 theread method depend on the particular type of the input stream.The methodreset for classInputStream does nothing except throw anIOException.
IOException - if this stream has not been marked or if the mark has been invalidated.mark(int),IOExceptionpublic boolean markSupported()
mark andreset methods. Whether or notmark andreset are supported is an invariant property of a particular input stream instance. ThemarkSupported method ofInputStream returnsfalse.