Java IO流源码学习之二（Buffered字节流）

本文记录BufferedInputStream，BufferedOutputStream两个带缓冲的输入输出流。

BufferedInputStream继承于FilterInputStream，BufferedOutputStream继承于FilterOutputStream，这两个类为具体的装饰类，而FilterInputStream与FilterOutputStream为抽象装饰者类，但是该两个类不是抽象类。

BufferedInputStream

下面是BufferedInputStream的源码：

public class BufferedInputStream extends FilterInputStream {//默认缓冲区大小private static int DEFAULT_BUFFER_SIZE = 8192;//最大缓冲区大小private static int MAX_BUFFER_SIZE = Integer.MAX_VALUE - 8;//内部缓冲数组protected volatile byte buf[];//为buf缓冲区提供原子的更新器private static finalAtomicReferenceFieldUpdater<BufferedInputStream, byte[]> bufUpdater =AtomicReferenceFieldUpdater.newUpdater(BufferedInputStream.class,  byte[].class, "buf");//该值表示缓冲区下一个接收Input Stream字节的位置protected int count;//缓冲区的当前位置，也就是下一个从缓冲区读数据的位置，该值小于等于countprotected int pos;//Mark标记的位置protected int markpos = -1;//pos - markpos > marklimit 时，Mark标记清除protected int marklimit;//获取该对象相应的InputStream对象private InputStream getInIfOpen() throws IOException {InputStream input = in;if (input == null)throw new IOException("Stream closed");return input;}//获取buf缓冲区private byte[] getBufIfOpen() throws IOException {byte[] buffer = buf;if (buffer == null)throw new IOException("Stream closed");return buffer;}//构造方法，调用父类方法，用于对InputStream 对象进行增强public BufferedInputStream(InputStream in) {this(in, DEFAULT_BUFFER_SIZE);}public BufferedInputStream(InputStream in, int size) {super(in);if (size <= 0) {throw new IllegalArgumentException("Buffer size <= 0");}buf = new byte[size];}//读入字节填充缓冲区private void fill() throws IOException {byte[] buffer = getBufIfOpen();//如果标记位无效，则直接填充缓冲区，并且覆盖原来的字节if (markpos < 0)pos = 0;            /* no mark: throw away the buffer */else if (pos >= buffer.length)  /* no room left in buffer */if (markpos > 0) {  /* can throw away early part of the buffer */int sz = pos - markpos;System.arraycopy(buffer, markpos, buffer, 0, sz);pos = sz;markpos = 0;} else if (buffer.length >= marklimit) {markpos = -1;   /* buffer got too big, invalidate mark */pos = 0;        /* drop buffer contents */} else if (buffer.length >= MAX_BUFFER_SIZE) {throw new OutOfMemoryError("Required array size too large");} else {            /* grow buffer */int nsz = (pos <= MAX_BUFFER_SIZE - pos) ?pos * 2 : MAX_BUFFER_SIZE;if (nsz > marklimit)nsz = marklimit;byte nbuf[] = new byte[nsz];System.arraycopy(buffer, 0, nbuf, 0, pos);if (!bufUpdater.compareAndSet(this, buffer, nbuf)) {// Can't replace buf if there was an async close.// Note: This would need to be changed if fill()// is ever made accessible to multiple threads.// But for now, the only way CAS can fail is via close.// assert buf == null;throw new IOException("Stream closed");}buffer = nbuf;}count = pos;int n = getInIfOpen().read(buffer, pos, buffer.length - pos);if (n > 0)count = n + pos;}//向缓冲区读取一个数据，若缓冲区没有数据，则使用fill方法填充缓冲区public synchronized int read() throws IOException {if (pos >= count) {fill();if (pos >= count)return -1;}return getBufIfOpen()[pos++] & 0xff;}//读取字节至相应数组（private方法）private int read1(byte[] b, int off, int len) throws IOException {int avail = count - pos;if (avail <= 0) {/* If the requested length is at least as large as the buffer, andif there is no mark/reset activity, do not bother to copy thebytes into the local buffer.  In this way buffered streams willcascade harmlessly. */if (len >= getBufIfOpen().length && markpos < 0) {return getInIfOpen().read(b, off, len);}fill();avail = count - pos;if (avail <= 0) return -1;}int cnt = (avail < len) ? avail : len;System.arraycopy(getBufIfOpen(), pos, b, off, cnt);pos += cnt;return cnt;}//读取相应字节至数组，为一个同步方法，线程安全public synchronized int read(byte b[], int off, int len)throws IOException{getBufIfOpen(); // Check for closed streamif ((off | len | (off + len) | (b.length - (off + len))) < 0) {throw new IndexOutOfBoundsException();} else if (len == 0) {return 0;}int n = 0;for (;;) {int nread = read1(b, off + n, len - n);if (nread <= 0)return (n == 0) ? nread : n;n += nread;if (n >= len)return n;// if not closed but no bytes available, returnInputStream input = in;if (input != null && input.available() <= 0)return n;}}//跳过n个字节public synchronized long skip(long n) throws IOException {getBufIfOpen(); // Check for closed streamif (n <= 0) {return 0;}long avail = count - pos;if (avail <= 0) {// If no mark position set then don't keep in bufferif (markpos <0)return getInIfOpen().skip(n);// Fill in buffer to save bytes for resetfill();avail = count - pos;if (avail <= 0)return 0;}long skipped = (avail < n) ? avail : n;pos += skipped;return skipped;}public synchronized int available() throws IOException {int n = count - pos;int avail = getInIfOpen().available();return n > (Integer.MAX_VALUE - avail)? Integer.MAX_VALUE: n + avail;}public synchronized void mark(int readlimit) {marklimit = readlimit;markpos = pos;}public synchronized void reset() throws IOException {getBufIfOpen(); // Cause exception if closedif (markpos < 0)throw new IOException("Resetting to invalid mark");pos = markpos;}public boolean markSupported() {return true;}public void close() throws IOException {byte[] buffer;while ( (buffer = buf) != null) {if (bufUpdater.compareAndSet(this, buffer, null)) {InputStream input = in;in = null;if (input != null)input.close();return;}// Else retry in case a new buf was CASed in fill()}}
}

BufferedOutputStream

public
class BufferedOutputStream extends FilterOutputStream {//buffer数组protected byte buf[];//buffer中有效值protected int count;public BufferedOutputStream(OutputStream out) {this(out, 8192);}public BufferedOutputStream(OutputStream out, int size) {super(out);if (size <= 0) {throw new IllegalArgumentException("Buffer size <= 0");}buf = new byte[size];}//清空缓冲区private void flushBuffer() throws IOException {if (count > 0) {out.write(buf, 0, count);count = 0;}}//写入一个字节至缓冲区public synchronized void write(int b) throws IOException {if (count >= buf.length) {flushBuffer();}buf[count++] = (byte)b;}//写入一个字节数组public synchronized void write(byte b[], int off, int len) throws IOException {//如果需要写入的长度大于缓冲区大小，则先清空缓冲区（将缓冲区所有字节写出），再写出该字节。if (len >= buf.length) {/* If the request length exceeds the size of the output buffer,flush the output buffer and then write the data directly.In this way buffered streams will cascade harmlessly. */flushBuffer();out.write(b, off, len);return;}//如果剩下的缓冲区容量放不下需要写入的字节长度，则把缓冲区字节写出if (len > buf.length - count) {flushBuffer();}//将相应字节数组复制至缓冲区System.arraycopy(b, off, buf, count, len);count += len;}//强制刷新缓冲，将缓冲内的数据写出至Output Streampublic synchronized void flush() throws IOException {flushBuffer();out.flush();}
}

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Java IO流源码学习之二（Buffered字节流）

BufferedInputStream

BufferedOutputStream

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