Okio的传送门
了解Okio之前先了解一个装饰者模式（就是java io的思路）
- 接下来简单模拟一个io操作
- 定义一个读取数据的接口，返回byte[ ]，BytesReader
- 定义一个它的实现类，用来读取byte[]，BytesReaderImpl
- 定义一个读取String的接口，用来读取StringReader
- 对BytesReaderImpl进行装饰，，让装饰类支持读取String，StringReaderImpl
继承关系图
- 看看具体的代码实现吧 _（ 比较简单）
ByteReader && ByteReaderImpl
public interface BytesReader {
byte[] readBytes(); //定义一个读取byte[]的数组
}
public class BytesReaderImpl implements BytesReader {
@Override
public byte[] readBytes() {
String str = "仅仅就是用来测试的字符串^_^...";
return str.getBytes();
}
}
StringReader && StringReaderImpl
public interface StringReader extends BytesReader{
String readString();
}
public class StringReaderImpl implements StringReader{
private BytesReader bytesReader;
public StringReaderImpl(BytesReader bytesReader) {
this.bytesReader = bytesReader;
}
@Override
public String readString() {
byte[] bytes = bytesReader.readBytes();
return new String(bytes);
}
@Override
public byte[] readBytes() {
return bytesReader.readBytes();
}
}
现在来看看okio的基本用法
public class Test {
public static void main(String[] args){
/* BytesReader bytesReader = new BytesReaderImpl();
StringReader stringReader = new StringReaderImpl(bytesReader);
System.out.println("readBytes : "+bytesReader.readBytes().length);
System.out.println("readString : "+stringReader.readString());*/
File file = new File("D://demo.txt");
File fileOut = new File("D://demo1.txt");
BufferedSink sink = null;
BufferedSource source = null;
try {
sink = Okio.buffer(Okio.sink(fileOut));
source = Okio.buffer(Okio.source(file));
byte[] buffer = new byte[12];
int temp = 0;
while((temp = source.read(buffer)) != -1){
System.out.println("temp : "+temp);
sink.write(buffer,0,temp);
}
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}finally {
try {
if(sink != null){
sink.close();
}
if(source != null){
source.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
- okio里面有一个，Source接口定义了读取数据的接口，类似InputStream
- okio里面还有一个，Sink接口定义了写数据的接口，类似OutputStream
- Source和Sink有两个实现类，BufferedSource 和 BufferedSink，这两个实现类定义了很多方法，包括文件的读写，字符串的读写，流的读写 等
- BufferedSource 和 BufferedSink有两个之类，RealBufferedSource和RealBufferedSink**，实际用的时候其实是用的这两个实现类
- Okio这个类提供了很多静态方法，简化上面这些类的创建操作
下面开始分析源代码
-
首先有一点是明白的，就是Source和Sink这两个类定义了顶层接口，一个用来读数据，一个用来写数据。
Source && Sinkpublic interface Source extends Closeable { long read(Buffer sink, long byteCount) throws IOException; Timeout timeout(); @Override void close() throws IOException; } public interface Sink extends Closeable, Flushable { void write(Buffer source, long byteCount) throws IOException; @Override void flush() throws IOException; /** Returns the timeout for this sink. */ Timeout timeout(); @Override void close() throws IOException; } -
Source和Sink分别有一个实现接口BufferedSource（接口）和BufferedSink（接口）,这两个接口就定义了更加偏向应用的常用接口，可以看到不管是读还是写都支持常见的类型，基本类型，String，而且Source接口和Sink接口接受的参数都是Buffer
public interface BufferedSink extends Sink { Buffer buffer(); BufferedSink write(ByteString byteString) throws IOException; BufferedSink write(byte[] source, int offset, int byteCount) throws IOException; BufferedSink writeUtf8(String string) throws IOException; BufferedSink writeShort(int s) throws IOException; ..... } public interface BufferedSource extends Source { byte readByte() throws IOException; short readShort() throws IOException; short readShortLe() throws IOException; String readUtf8() throws IOException; ..... }
- 可以看到不管是Source还是Sink接受的参数都是Buffer [okio.Buffer]，所以说Buffer在okio的读写种起着媒介（比较重要）的作用，Buffer的代码有点多（1600+行）就提出一些比较重要的来说
public final class Buffer implements BufferedSource, BufferedSink, Cloneable {
Segment head;
long size;
@Override public OutputStream outputStream() {
return new OutputStream() {
@Override public void write(int b) {
writeByte((byte) b);
}
@Override public void write(byte[] data, int offset, int byteCount) {
Buffer.this.write(data, offset, byteCount);
}
@Override public void flush(){}
@Override public void close() {}
@Override public String toString() {
return Buffer.this + ".outputStream()";
}
};
}
...
@Override public InputStream inputStream() {
return new InputStream() {
@Override public int read() {
if (size > 0) return readByte() & 0xff;
return -1;
}
@Override public int read(byte[] sink, int offset, int byteCount) {
return Buffer.this.read(sink, offset, byteCount);
}
@Override public int available() {
return (int) Math.min(size, Integer.MAX_VALUE);
}
@Override public void close() {
}
@Override public String toString() {
return Buffer.this + ".inputStream()";
}
};
}
....
}
- 先简单的说哈后面在回过来说，这里Buffer其实既有读的功能也有写的功能，但是我们的程序里面其实是可以像调用java io的api一样，因为里面包装了一个OutputStream和InputStream ，这里还引入了一个新的对象，**Segment**
-
有了大概的了解，就来看看继承图
okio部分类的继承图
继续啊
- 我们构造BufferedSource是使用的是Okio.buffer(Okio.sink(fileOut));
- 首先来看Okio.sink(fileOut),其实内部就一句，return sink(new FileOutputStream(file));，构造了一个FileOutputStream并调用了，sink（OutputStream out）方法,最终调用了sink(OutputStream out, Timeout timeout) 这个方法,其实就是构造了一个Sink接口对象并返回。
private static Sink sink(final OutputStream out, final Timeout timeout) { if (out == null) throw new IllegalArgumentException("out == null"); if (timeout == null) throw new IllegalArgumentException("timeout == null"); return new Sink() { @Override public void write(Buffer source, long byteCount) throws IOException { checkOffsetAndCount(source.size, 0, byteCount); while (byteCount > 0) { timeout.throwIfReached(); Segment head = source.head; int toCopy = (int) Math.min(byteCount, head.limit - head.pos); out.write(head.data, head.pos, toCopy); head.pos += toCopy; byteCount -= toCopy; source.size -= toCopy; if (head.pos == head.limit) { source.head = head.pop(); SegmentPool.recycle(head); } } } @Override public void flush() throws IOException { out.flush(); } @Override public void close() throws IOException { out.close(); } @Override public Timeout timeout() { return timeout; } @Override public String toString() { return "sink(" + out + ")"; } }; }
上面的Sink返回了以后传递给了Okio.buffer方法，这个方法里面实际就是实例化了一个RealBufferedSink对象并返回。代码就不贴了，说哈RealBufferedSink大概做了些什么，首先是RealBufferedSink里面包含了一个Buffer（可读可写）对象，在调用RealBufferedSink的时候，实际上就是调用的Buffer对象的write方法。
BufferedSource和BufferedSink的处理是类似的这里就不啰嗦了。
小结前面提到的流程
- 在构造BufferedSource的时候会传递一个Source到Okio.buffer方法里面，而这个Source是一个匿名内部类来实例化的，并且里面使用FileInputStream去读取数据，然后吧数据保存到传入的Buffer参数里面，而这个Buffer是支持读写的。所以BufferedSource读取Buffer里面的数据，Buffer获取从FileInputStream里面的数据。从这里就可以看出来，Okio效率高就是这个Buffer在起作用，前面大概说了哈Buffer，它里面还有一个重要的对象还没有说Segment
继续哈
- Segment对象，Segment的源码不是很多，实现的实现其实就是一个双向链表。里面定义了一个byte[]和前一个节点的引用以及后一个节点的引用
final class Segment {
/** The size of all segments in bytes. */
static final int SIZE = 8192;
/** Segments will be shared when doing so avoids {@code arraycopy()} of this many bytes. */
static final int SHARE_MINIMUM = 1024;
final byte[] data;
int pos;
int limit;
boolean shared;
boolean owner;
Segment next;
Segment prev;
Segment() {
this.data = new byte[SIZE];
this.owner = true;
this.shared = false;
}
...
public Segment pop() {
Segment result = next != this ? next : null;
prev.next = next;
next.prev = prev;
next = null;
prev = null;
return result;
}
public Segment push(Segment segment) {
segment.prev = this;
segment.next = next;
next.prev = segment;
next = segment;
return segment;
}
...
public void writeTo(Segment sink, int byteCount) {
if (!sink.owner) throw new IllegalArgumentException();
if (sink.limit + byteCount > SIZE) {
// We can't fit byteCount bytes at the sink's current position. Shift sink first.
if (sink.shared) throw new IllegalArgumentException();
if (sink.limit + byteCount - sink.pos > SIZE) throw new IllegalArgumentException();
System.arraycopy(sink.data, sink.pos, sink.data, 0, sink.limit - sink.pos);
sink.limit -= sink.pos;
sink.pos = 0;
}
System.arraycopy(data, pos, sink.data, sink.limit, byteCount);
sink.limit += byteCount;
pos += byteCount;
}
}
- 现在可以来看看Buffer里面是怎么处理数据的了，就挑一个read方法,其实就是直接将传入的byte数据copy到了segment里面，这里又出来了一个新的类SegmentPool
@Override public int read(byte[] sink, int offset, int byteCount) {
checkOffsetAndCount(sink.length, offset, byteCount);
Segment s = head;
if (s == null) return -1;
int toCopy = Math.min(byteCount, s.limit - s.pos);
System.arraycopy(s.data, s.pos, sink, offset, toCopy);
s.pos += toCopy;
size -= toCopy;
if (s.pos == s.limit) {
head = s.pop();
SegmentPool.recycle(s);
}
return toCopy;
}
- SegmentPool就是一个回收池~~，读取和写入不断的回收利用，同一个byte[]多次利用。
最后贴一个okio的整个继承图吧
点击查看大图
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