Android APIs
public abstract class

InputStream

extends Object
implements Closeable
java.lang.Object
   ↳ java.io.InputStream
Known Direct Subclasses
Known Indirect Subclasses

Class Overview

A readable source of bytes.

Most clients will use input streams that read data from the file system (FileInputStream), the network (getInputStream()/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.

Subclassing InputStream

Subclasses that decorate another input stream should consider subclassing 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.

See Also

Summary

Public Constructors
InputStream()
This constructor does nothing.
Public Methods
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.
int read(byte[] buffer)
Equivalent to read(buffer, 0, buffer.length).
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, int byteOffset, int byteCount)
Reads up to byteCount bytes from this stream and stores them in the byte array buffer starting at byteOffset.
void reset()
Resets this stream to the last marked location.
long skip(long byteCount)
Skips at most byteCount bytes in this stream.
[Expand]
Inherited Methods
From class java.lang.Object
From interface java.io.Closeable
From interface java.lang.AutoCloseable

Public Constructors

public InputStream ()

Added in API level 1

This constructor does nothing. It is provided for signature compatibility.

Public Methods

public int available ()

Added in API level 1

Returns an estimated number of bytes that can be read or skipped without blocking for more input.

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, 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.

Returns
  • the estimated number of bytes available
Throws
IOException if this stream is closed or an error occurs

public void close ()

Added in API level 1

Closes this stream. Concrete implementations of this class should free any resources during close. This implementation does nothing.

Throws
IOException if an error occurs while closing this stream.

public void mark (int readlimit)

Added in API level 1

Sets a mark position in this InputStream. The parameter 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.

Parameters
readlimit the number of bytes that can be read from this stream before the mark is invalidated.

public boolean markSupported ()

Added in API level 1

Indicates whether this stream supports the mark() and reset() methods. The default implementation returns false.

Returns
  • always false.
See Also

public int read (byte[] buffer)

Added in API level 1

Equivalent to read(buffer, 0, buffer.length).

Throws
IOException

public abstract int read ()

Added in API level 1

Reads a single byte from this stream and returns it as an integer in the range from 0 to 255. Returns -1 if the end of the stream has been reached. Blocks until one byte has been read, the end of the source stream is detected or an exception is thrown.

Throws
IOException if the stream is closed or another IOException occurs.

public int read (byte[] buffer, int byteOffset, int byteCount)

Added in API level 1

Reads up to byteCount bytes from this stream and stores them in the byte array buffer starting at byteOffset. Returns the number of bytes actually read or -1 if the end of the stream has been reached.

Throws
IndexOutOfBoundsException if byteOffset < 0 || byteCount < 0 || byteOffset + byteCount > buffer.length.
IOException if the stream is closed or another IOException occurs.

public void reset ()

Added in API level 1

Resets this stream to the last marked location. Throws an 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.

Throws
IOException if this stream is closed or another IOException occurs.

public long skip (long byteCount)

Added in API level 1

Skips at most byteCount bytes in this stream. The number of actual bytes skipped may be anywhere between 0 and byteCount. If byteCount is negative, this method does nothing and returns 0, 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.

Returns
  • the number of bytes actually skipped.
Throws
IOException if this stream is closed or another IOException occurs.