Java IO学习之缓冲输入流（BufferedInputStream）

BufferedInputStream(InputStream in) BufferedInputStream(InputStream in, int size) synchronized int available() void close() synchronized void mark(int readlimit) boolean markSupported() synchronized int read() synchronized int read(byte[] buffer, int offset, int byteCount) synchronized void reset() synchronized long skip(long byteCount) 

public class BufferedInputStreamTest {    private static final int LEN = 5;    public static void main(String[] args) {     testBufferedInputStream() ;   }   private static void testBufferedInputStream() {      // 创建BufferedInputStream字节流，内容是ArrayLetters数组     try {       File file = new File("file.txt");       InputStream in =new BufferedInputStream(new FileInputStream(file), 512);        // 从字节流中读取5个字节。“abcde”，a对应0x61，b对应0x62，依次类推...       for (int i=0; i<LEN; i++) {       // 若能继续读取下一个字节，则读取下一个字节         if (in.available() >= 0) {         // 读取“字节流的下一个字节”         int tmp = in.read();         System.out.printf("%d : 0x%s/n", i, Integer.toHexString(tmp));         }       }        // 若“该字节流”不支持标记功能，则直接退出       if (!in.markSupported()) {         System.out.println("make not supported!");         return ;       }        // 标记“当前索引位置”，即标记第6个位置的元素--“f”       // 1024对应marklimit       in.mark(1024);        // 跳过22个字节。       in.skip(22);        // 读取5个字节       byte[] buf = new byte[LEN];       in.read(buf, 0, LEN);       // 将buf转换为String字符串。       String str1 = new String(buf);       System.out.printf("str1=%s/n", str1);        // 重置“输入流的索引”为mark()所标记的位置，即重置到“f”处。       in.reset();       // 从“重置后的字节流”中读取5个字节到buf中。即读取“fghij”       in.read(buf, 0, LEN);       // 将buf转换为String字符串。       String str2 = new String(buf);       System.out.printf("str2=%s/n", str2);        in.close();     } catch (FileNotFoundException e) {       e.printStackTrace();     } catch (SecurityException e) {       e.printStackTrace();     } catch (IOException e) {       e.printStackTrace();     }   } } 

0 : 0x611 : 0x622 : 0x633 : 0x644 : 0x65str1=12345str2=fghij

public class BufferedInputStream extends FilterInputStream {    private static int DEFAULT_BUFFER_SIZE = 8192;//默认缓冲区大小为8X1024   private static int MAX_BUFFER_SIZE = Integer.MAX_VALUE - 8;   protected volatile byte buf[]; //缓冲数组    /**    * Atomic updater to provide compareAndSet for buf. This is    * necessary because closes can be asynchronous. We use nullness    * of buf[] as primary indicator that this stream is closed. (The    * "in" field is also nulled out on close.)    */   private static final AtomicReferenceFieldUpdater<BufferedInputStream, byte[]> bufUpdater =       AtomicReferenceFieldUpdater.newUpdater(BufferedInputStream.class, byte[].class, "buf");   //值在0到buf.len之间   protected int count;   //在buffer的当前位置，下一个字符被读取   protected int pos;   //值为mark函数最近被调用的时候，值为-1到pos   protected int markpos = -1;    /**    * The maximum read ahead allowed after a call to the    * <code>mark</code> method before subsequent calls to the    * <code>reset</code> method fail.    * Whenever the difference between <code>pos</code>    * and <code>markpos</code> exceeds <code>marklimit</code>,    * then the mark may be dropped by setting    * <code>markpos</code> to <code>-1</code>.    *    * @see   java.io.BufferedInputStream#mark(int)    * @see   java.io.BufferedInputStream#reset()    */    protected int marklimit;    /**    * Check to make sure that underlying input stream has not been    * nulled out due to close; if not return it;    */   //   private InputStream getInIfOpen() throws IOException {     InputStream input = in;     if (input == null)       throw new IOException("Stream closed");     return input;   }    /**    * Check to make sure that buffer has not been nulled out due to    * close; if not return it;    */   private byte[] getBufIfOpen() throws IOException {     byte[] buffer = buf;     if (buffer == null)       throw new IOException("Stream closed");     return buffer;   }    /**    * Creates a <code>BufferedInputStream</code>    * and saves its argument, the input stream    * <code>in</code>, for later use. An internal    * buffer array is created and stored in <code>buf</code>.    *    * @param  in  the underlying input stream.    */   //带InputStream的构造函数   public BufferedInputStream(InputStream in) {       this(in, DEFAULT_BUFFER_SIZE);   }    /**    * Creates a <code>BufferedInputStream</code>    * with the specified buffer size,    * and saves its argument, the input stream    * <code>in</code>, for later use. An internal    * buffer array of length <code>size</code>    * is created and stored in <code>buf</code>.    *    * @param  in   the underlying input stream.    * @param  size  the buffer size.    * @exception IllegalArgumentException if {@code size <= 0}.    */   //带InputStream和大小的构造函数   public BufferedInputStream(InputStream in, int size) {     super(in);     if (size <= 0) {         throw new IllegalArgumentException("Buffer size <= 0");     }     buf = new byte[size];   }    /**    * Fills the buffer with more data, taking into account    * shuffling and other tricks for dealing with marks.    * Assumes that it is being called by a synchronized method.    * This method also assumes that all data has already been read in,    * hence pos > count.    */   //   private void fill() throws IOException {     byte[] buffer = getBufIfOpen();     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;     }    /**    * See    * the general contract of the <code>read</code>    * method of <code>InputStream</code>.    *    * @return   the next byte of data, or <code>-1</code> if the end of the    *       stream is reached.    * @exception IOException if this input stream has been closed by    *             invoking its {@link #close()} method,    *             or an I/O error occurs.    * @see    java.io.FilterInputStream#in    */   //读下一个字节，没有数据返回-1   public synchronized int read() throws IOException {     if (pos >= count) {       fill();       if (pos >= count)         return -1;     }     return getBufIfOpen()[pos++] & 0xff;   }    /**    * Read characters into a portion of an array, reading from the underlying    * stream at most once if necessary.    */   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, and         if there is no mark/reset activity, do not bother to copy the         bytes into the local buffer. In this way buffered streams will         cascade 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;   }    /**    * Reads bytes from this byte-input stream into the specified byte array,    * starting at the given offset.    *    * <p> This method implements the general contract of the corresponding    * <code>{@link InputStream#read(byte[], int, int) read}</code> method of    * the <code>{@link InputStream}</code> class. As an additional    * convenience, it attempts to read as many bytes as possible by repeatedly    * invoking the <code>read</code> method of the underlying stream. This    * iterated <code>read</code> continues until one of the following    * conditions becomes true: <ul>    *    *  <li> The specified number of bytes have been read,    *    *  <li> The <code>read</code> method of the underlying stream returns    *  <code>-1</code>, indicating end-of-file, or    *    *  <li> The <code>available</code> method of the underlying stream    *  returns zero, indicating that further input requests would block.    *    * </ul> If the first <code>read</code> on the underlying stream returns    * <code>-1</code> to indicate end-of-file then this method returns    * <code>-1</code>. Otherwise this method returns the number of bytes    * actually read.    *    * <p> Subclasses of this class are encouraged, but not required, to    * attempt to read as many bytes as possible in the same fashion.    *    * @param   b   destination buffer.    * @param   off  offset at which to start storing bytes.    * @param   len  maximum number of bytes to read.    * @return   the number of bytes read, or <code>-1</code> if the end of    *       the stream has been reached.    * @exception IOException if this input stream has been closed by    *             invoking its {@link #close()} method,    *             or an I/O error occurs.    */   //   public synchronized int read(byte b[], int off, int len)throws IOException   {     getBufIfOpen(); // Check for closed stream     if ((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, return       InputStream input = in;       if (input != null && input.available() <= 0)         return n;     }   }    /**    * See the general contract of the <code>skip</code>    * method of <code>InputStream</code>.    *    * @exception IOException if the stream does not support seek,    *             or if this input stream has been closed by    *             invoking its {@link #close()} method, or an    *             I/O error occurs.    */   //跳过n长的数据   public synchronized long skip(long n) throws IOException {     getBufIfOpen(); // Check for closed stream     if (n <= 0) {       return 0;     }     long avail = count - pos;      if (avail <= 0) {       // If no mark position set then don't keep in buffer       if (markpos <0)         return getInIfOpen().skip(n);        // Fill in buffer to save bytes for reset       fill();       avail = count - pos;       if (avail <= 0)         return 0;     }      long skipped = (avail < n) ? avail : n;     pos += skipped;     return skipped;   }    /**    * Returns an estimate of the number of bytes that can be read (or    * skipped over) from this input stream without blocking by the next    * invocation of a method for this input stream. The next invocation might be    * the same thread or another thread. A single read or skip of this    * many bytes will not block, but may read or skip fewer bytes.    * <p>    * This method returns the sum of the number of bytes remaining to be read in    * the buffer (<code>count - pos</code>) and the result of calling the    * {@link java.io.FilterInputStream#in in}.available().    *    * @return   an estimate of the number of bytes that can be read (or skipped    *       over) from this input stream without blocking.    * @exception IOException if this input stream has been closed by    *             invoking its {@link #close()} method,    *             or an I/O error occurs.    */   //返回还有多少数据可以读   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;   }    /**    * See the general contract of the <code>mark</code>    * method of <code>InputStream</code>.    *    * @param  readlimit  the maximum limit of bytes that can be read before    *           the mark position becomes invalid.    * @see   java.io.BufferedInputStream#reset()    */   public synchronized void mark(int readlimit) {     marklimit = readlimit;     markpos = pos;   }    /**    * See the general contract of the <code>reset</code>    * method of <code>InputStream</code>.    * <p>    * If <code>markpos</code> is <code>-1</code>    * (no mark has been set or the mark has been    * invalidated), an <code>IOException</code>    * is thrown. Otherwise, <code>pos</code> is    * set equal to <code>markpos</code>.    *    * @exception IOException if this stream has not been marked or,    *         if the mark has been invalidated, or the stream    *         has been closed by invoking its {@link #close()}    *         method, or an I/O error occurs.    * @see    java.io.BufferedInputStream#mark(int)    */   public synchronized void reset() throws IOException {     getBufIfOpen(); // Cause exception if closed     if (markpos < 0)       throw new IOException("Resetting to invalid mark");     pos = markpos;   }    /**    * Tests if this input stream supports the <code>mark</code>    * and <code>reset</code> methods. The <code>markSupported</code>    * method of <code>BufferedInputStream</code> returns    * <code>true</code>.    *    * @return a <code>boolean</code> indicating if this stream type supports    *     the <code>mark</code> and <code>reset</code> methods.    * @see   java.io.InputStream#mark(int)    * @see   java.io.InputStream#reset()    */   //是否支持标记   public boolean markSupported() {     return true;   }    /**    * Closes this input stream and releases any system resources    * associated with the stream.    * Once the stream has been closed, further read(), available(), reset(),    * or skip() invocations will throw an IOException.    * Closing a previously closed stream has no effect.    *    * @exception IOException if an I/O error occurs.    */   //关闭资源    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()     }   } }