java.io.InputStream Maven / Gradle / Ivy

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This work corresponds to the API signatures of JSR 219: Foundation Profile 1.1. In the event of a discrepency between this work and the JSR 219 specification, which is available at http://www.jcp.org/en/jsr/detail?id=219, the latter takes precedence. */ 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 * @version 1.36, 02/02/00 * @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 { public InputStream() { } /** * 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. * * @return the next byte of data, or -1 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 b is null, a * NullPointerException 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 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[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. * *

If the first byte cannot be read for any reason other than end of * file, then an IOException is thrown. In particular, an * IOException is thrown if the input stream has been closed. * *

The read(b) method for class InputStream * has the same effect as:

 read(b, 0, b.length) 

This method blocks until input data is available, end of file is * detected, or an exception is thrown. * *

If b is null, a * NullPointerException is thrown. * *

If off is negative, or len is negative, or * off+len is greater than the length of the array * b, then an IndexOutOfBoundsException 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. * *

If the first byte cannot be read for any reason other than end of * file, then an IOException is thrown. In particular, an * IOException is thrown if the input stream has been closed. * *

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. 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 b * 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 * -1 if there is no more data because the end of * the stream has been reached. * @exception IOException if an I/O error occurs. * @exception NullPointerException if b is null. * @see java.io.InputStream#read() */ public int read(byte[] b, int off, int len) throws IOException { return 0; } /** * 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, no bytes are skipped. * *

The skip method of InputStream 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. * * @param n the number of bytes to be skipped. * @return the actual number of bytes skipped. * @exception IOException if an I/O error occurs. */ public long skip(long n) throws IOException { return -1; } /** * Returns the number of bytes that can be read (or skipped over) from * this input stream without blocking by the next caller of a method for * this input stream. The next caller might be the same thread or or * another thread. * *

The available method for class InputStream * always returns 0. * *

This method should be overridden by subclasses. * * @return the number of bytes that can be read from this input stream * without blocking. * @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. * * @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. * *

The mark method of InputStream 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.