Okio is a new library that complements java.io
and java.nio
to make it much
easier to access, store, and process your data.
Okio is built around two types that pack a lot of capability into a straightforward API:
-
ByteString is an immutable sequence of bytes. For character data,
String
is fundamental.ByteString
is String's long-lost brother, making it easy to treat binary data as a value. This class is ergonomic: it knows how to encode and decode itself as hex, base64, and UTF-8. -
Buffer is a mutable sequence of bytes. Like
ArrayList
, you don't need to size your buffer in advance. You read and write buffers as a queue: write data to the end and read it from the front. There's no obligation to manage positions, limits, or capacities.
Internally, ByteString
and Buffer
do some clever things to save CPU and
memory. If you encode a UTF-8 string as a ByteString
, it caches a reference to
that string so that if you decode it later, there's no work to do.
Buffer
is implemented as a linked list of segments. When you move data from
one buffer to another, it reassigns ownership of the segments rather than
copying the data across. This approach is particularly helpful for multithreaded
programs: a thread that talks to the network can exchange data with a worker
thread without any copying or ceremony.
An elegant part of the java.io
design is how streams can be layered for
transformations like encryption and compression. Okio includes its own stream
types called Source
and Sink
that work like InputStream
and
OutputStream
, but with some key differences:
-
Timeouts. The streams provide access to the timeouts of the underlying I/O mechanism. Unlike the
java.io
socket streams, bothread()
andwrite()
calls honor timeouts. -
Easy to implement.
Source
declares three methods:read()
,close()
, andtimeout()
. There are no hazards likeavailable()
or single-byte reads that cause correctness and performance surprises. -
Easy to use. Although implementations of
Source
andSink
have only three methods to write, callers are given a rich API with theBufferedSource
andBufferedSink
interfaces. These interfaces give you everything you need in one place. -
No artificial distinction between byte streams and char streams. It's all data. Read and write it as bytes, UTF-8 strings, big-endian 32-bit integers, little-endian shorts; whatever you want. No more
InputStreamReader
! -
Easy to test. The
Buffer
class implements bothBufferedSource
andBufferedSink
so your test code is simple and clear.
Sources and sinks interoperate with InputStream
and OutputStream
. You can
view any Source
as an InputStream
, and you can view any InputStream
as a
Source
. Similarly for Sink
and OutputStream
.
Okio started as a component of OkHttp, the capable HTTP+SPDY client included in Android. It's well-exercised and ready to solve new problems.
Decoding the chunks of a PNG file demonstrates Okio in practice.
private static final ByteString PNG_HEADER = ByteString.decodeHex("89504e470d0a1a0a");
public void decodePng(InputStream in) throws IOException {
BufferedSource pngSource = Okio.buffer(Okio.source(in));
ByteString header = pngSource.readByteString(PNG_HEADER.size());
if (!header.equals(PNG_HEADER)) {
throw new IOException("Not a PNG.");
}
while (true) {
Buffer chunk = new Buffer();
// Each chunk is a length, type, data, and CRC offset.
int length = pngSource.readInt();
String type = pngSource.readUtf8(4);
pngSource.readFully(chunk, length);
int crc = pngSource.readInt();
decodeChunk(type, chunk);
if (type.equals("IEND")) break;
}
pngSource.close();
}
private void decodeChunk(String type, Buffer chunk) {
if (type.equals("IHDR")) {
int width = chunk.readInt();
int height = chunk.readInt();
System.out.printf("%08x: %s %d x %d%n", chunk.size(), type, width, height);
} else {
System.out.printf("%08x: %s%n", chunk.size(), type);
}
}
Download the latest JAR or grab via Maven:
<dependency>
<groupId>com.squareup.okio</groupId>
<artifactId>okio</artifactId>
<version>1.5.0</version>
</dependency>
or Gradle:
compile 'com.squareup.okio:okio:1.5.0'
Snapshots of the development version are available in Sonatype's snapshots
repository.
okio's People
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