java.io.InputStream Maven / Gradle / Ivy
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package java.io;
import java.util.Arrays;
import libcore.io.Streams;
/**
* A readable source of bytes.
*
* Most clients will use input streams that read data from the file system
* ({@link FileInputStream}), the network ({@link java.net.Socket#getInputStream()}/{@link
* java.net.HttpURLConnection#getInputStream()}), or from an in-memory byte
* array ({@link ByteArrayInputStream}).
*
*
Use {@link InputStreamReader} to adapt a byte stream like this one into a
* character stream.
*
*
Most clients should wrap their input stream with {@link
* 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 {@link #markSupported()} and throw an {@link IOException} when
* {@link #reset()} is called.
*
*
Subclassing InputStream
* Subclasses that decorate another input stream should consider subclassing
* {@link FilterInputStream}, which delegates all calls to the source input
* stream.
*
* All input stream subclasses should override both {@link
* #read() read()} and {@link #read(byte[],int,int) 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 OutputStream
*/
public abstract class InputStream extends Object implements Closeable {
/**
* This constructor does nothing. It is provided for signature
* compatibility.
*/
public InputStream() {
/* empty */
}
/**
* 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
* {@link ByteArrayOutputStream} and convert that to a byte array. Alternatively, if you're
* reading from a file, {@link 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 {@code InputStream} always returns 0.
* Subclasses should override this method if they are able to indicate the number of bytes
* available.
*
* @return the estimated number of bytes available
* @throws IOException if this stream is closed or an error occurs
*/
public int available() throws IOException {
return 0;
}
/**
* 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 close() throws IOException {
/* empty */
}
/**
* Sets a mark position in this InputStream. The parameter {@code readlimit}
* indicates how many bytes can be read before the mark is invalidated.
* Sending {@code reset()} will reposition the stream back to the marked
* position provided {@code readLimit} has not been surpassed.
*
* This default implementation does nothing and concrete subclasses must
* provide their own implementation.
*
* @param readlimit
* the number of bytes that can be read from this stream before
* the mark is invalidated.
* @see #markSupported()
* @see #reset()
*/
public void mark(int readlimit) {
/* empty */
}
/**
* Indicates whether this stream supports the {@code mark()} and
* {@code reset()} methods. The default implementation returns {@code false}.
*
* @return always {@code false}.
* @see #mark(int)
* @see #reset()
*/
public boolean markSupported() {
return false;
}
/**
* 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 abstract int read() throws IOException;
/**
* Equivalent to {@code read(buffer, 0, buffer.length)}.
*/
public int read(byte[] buffer) throws IOException {
return read(buffer, 0, buffer.length);
}
/**
* Reads up to {@code byteCount} bytes from this stream and stores them in
* the byte array {@code buffer} starting at {@code byteOffset}.
* Returns the number of bytes actually read or -1 if the end of the stream
* has been reached.
*
* @throws IndexOutOfBoundsException
* if {@code byteOffset < 0 || byteCount < 0 || byteOffset + byteCount > buffer.length}.
* @throws IOException
* if the stream is closed or another IOException occurs.
*/
public int read(byte[] buffer, int byteOffset, int byteCount) throws IOException {
Arrays.checkOffsetAndCount(buffer.length, byteOffset, byteCount);
for (int i = 0; i < byteCount; ++i) {
int c;
try {
if ((c = read()) == -1) {
return i == 0 ? -1 : i;
}
} catch (IOException e) {
if (i != 0) {
return i;
}
throw e;
}
buffer[byteOffset + i] = (byte) c;
}
return byteCount;
}
/**
* Resets this stream to the last marked location. Throws an
* {@code IOException} if the number of bytes read since the mark has been
* set is greater than the limit provided to {@code mark}, or if no mark
* has been set.
*
* This implementation always throws an {@code IOException} and concrete
* subclasses should provide the proper implementation.
*
* @throws IOException
* if this stream is closed or another IOException occurs.
*/
public synchronized void reset() throws IOException {
throw new IOException();
}
/**
* Skips at most {@code n} bytes in this stream. This method does nothing and returns
* 0 if {@code 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.
*
* @param byteCount the number of bytes to skip.
* @return the number of bytes actually skipped.
* @throws IOException
* if this stream is closed or another IOException occurs.
*/
public long skip(long byteCount) throws IOException {
return Streams.skipByReading(this, byteCount);
}
}