OutputStream 类实现关系

本文主要从 JDK 源码角度分析 OutputStream。 @Eason Gao

OutputStream 类实现关系

OutputStream 抽象类

OutputStream 类

 public abstract void write(int b)
 // 写入一个字节，可以看到这里的参数是一个 int 类型，对应上面的读方法，int 类型的 32 位，只有低 8 位才写入，高 24 位将舍弃。
 
 public void write(byte b[])
 // 将数组中的所有字节写入，和上面对应的 read() 方法类似，实际调用的也是下面的方法。
 
 public void write(byte b[], int off, int len)
 // 将 byte 数组从 off 位置开始，len 长度的字节写入
 
 public void flush()
 // 强制刷新，将缓冲中的数据写入
 
 public void close()
 // 关闭输出流，流被关闭后就不能再输出数据了
​

源码实现

FilterOutputStream

 /**
  * This class is the superclass of all classes that filter output
  * streams. These streams sit on top of an already existing output
  * stream (the <i>underlying</i> output stream) which it uses as its
  * basic sink of data, but possibly transforming the data along the
  * way or providing additional functionality.
  * <p>
  * The class <code>FilterOutputStream</code> itself simply overrides
  * all methods of <code>OutputStream</code> with versions that pass
  * all requests to the underlying output stream. Subclasses of
  * <code>FilterOutputStream</code> may further override some of these
  * methods as well as provide additional methods and fields.
  *
  * @author  Jonathan Payne
  * @since   JDK1.0
  */
 public
 class FilterOutputStream extends OutputStream {
     /**
      * The underlying output stream to be filtered.
      */
     protected OutputStream out;
 
     /**
      * Creates an output stream filter built on top of the specified
      * underlying output stream.
      *
      * @param   out   the underlying output stream to be assigned to
      *                the field <tt>this.out</tt> for later use, or
      *                <code>null</code> if this instance is to be
      *                created without an underlying stream.
      */
     public FilterOutputStream(OutputStream out) {
         this.out = out;
     }
 
     /**
      * Writes the specified <code>byte</code> to this output stream.
      * <p>
      * The <code>write</code> method of <code>FilterOutputStream</code>
      * calls the <code>write</code> method of its underlying output stream,
      * that is, it performs <tt>out.write(b)</tt>.
      * <p>
      * Implements the abstract <tt>write</tt> method of <tt>OutputStream</tt>.
      *
      * @param      b   the <code>byte</code>.
      * @exception  IOException  if an I/O error occurs.
      */
     public void write(int b) throws IOException {
         out.write(b);
     }
 
     /**
      * Writes <code>b.length</code> bytes to this output stream.
      * <p>
      * The <code>write</code> method of <code>FilterOutputStream</code>
      * calls its <code>write</code> method of three arguments with the
      * arguments <code>b</code>, <code>0</code>, and
      * <code>b.length</code>.
      * <p>
      * Note that this method does not call the one-argument
      * <code>write</code> method of its underlying stream with the single
      * argument <code>b</code>.
      *
      * @param      b   the data to be written.
      * @exception  IOException  if an I/O error occurs.
      * @see        java.io.FilterOutputStream#write(byte[], int, int)
      */
     public void write(byte b[]) throws IOException {
         write(b, 0, b.length);
     }
 
     /**
      * Writes <code>len</code> bytes from the specified
      * <code>byte</code> array starting at offset <code>off</code> to
      * this output stream.
      * <p>
      * The <code>write</code> method of <code>FilterOutputStream</code>
      * calls the <code>write</code> method of one argument on each
      * <code>byte</code> to output.
      * <p>
      * Note that this method does not call the <code>write</code> method
      * of its underlying input stream with the same arguments. Subclasses
      * of <code>FilterOutputStream</code> should provide a more efficient
      * implementation of this method.
      *
      * @param      b     the data.
      * @param      off   the start offset in the data.
      * @param      len   the number of bytes to write.
      * @exception  IOException  if an I/O error occurs.
      * @see        java.io.FilterOutputStream#write(int)
      */
     public void write(byte b[], int off, int len) throws IOException {
         if ((off | len | (b.length - (len + off)) | (off + len)) < 0)
             throw new IndexOutOfBoundsException();
 
         for (int i = 0 ; i < len ; i++) {
             write(b[off + i]);
         }
     }
 
     /**
      * Flushes this output stream and forces any buffered output bytes
      * to be written out to the stream.
      * <p>
      * The <code>flush</code> method of <code>FilterOutputStream</code>
      * calls the <code>flush</code> method of its underlying output stream.
      *
      * @exception  IOException  if an I/O error occurs.
      * @see        java.io.FilterOutputStream#out
      */
     public void flush() throws IOException {
         out.flush();
     }
 
     /**
      * Closes this output stream and releases any system resources
      * associated with the stream.
      * <p>
      * The <code>close</code> method of <code>FilterOutputStream</code>
      * calls its <code>flush</code> method, and then calls the
      * <code>close</code> method of its underlying output stream.
      *
      * @exception  IOException  if an I/O error occurs.
      * @see        java.io.FilterOutputStream#flush()
      * @see        java.io.FilterOutputStream#out
      */
     @SuppressWarnings("try")
     public void close() throws IOException {
         try (OutputStream ostream = out) {
             flush();
         }
     }
 }
​

ByteArrayOutputStream

 /**
  * This class implements an output stream in which the data is
  * written into a byte array. The buffer automatically grows as data
  * is written to it.
  * The data can be retrieved using <code>toByteArray()</code> and
  * <code>toString()</code>.
  * <p>
  * Closing a <tt>ByteArrayOutputStream</tt> has no effect. The methods in
  * this class can be called after the stream has been closed without
  * generating an <tt>IOException</tt>.
  *
  * @author  Arthur van Hoff
  * @since   JDK1.0
  */
 
 public class ByteArrayOutputStream extends OutputStream {
 
     /**
      * The buffer where data is stored.
      */
     protected byte buf[];
 
     /**
      * The number of valid bytes in the buffer.
      */
     protected int count;
 
     /**
      * Creates a new byte array output stream. The buffer capacity is
      * initially 32 bytes, though its size increases if necessary.
      */
     public ByteArrayOutputStream() {
         this(32);
     }
 
     /**
      * Creates a new byte array output stream, with a buffer capacity of
      * the specified size, in bytes.
      *
      * @param   size   the initial size.
      * @exception  IllegalArgumentException if size is negative.
      */
     public ByteArrayOutputStream(int size) {
         if (size < 0) {
             throw new IllegalArgumentException("Negative initial size: "
                                                + size);
         }
         buf = new byte[size];
     }
 
     /**
      * Increases the capacity if necessary to ensure that it can hold
      * at least the number of elements specified by the minimum
      * capacity argument.
      *
      * @param minCapacity the desired minimum capacity
      * @throws OutOfMemoryError if {@code minCapacity < 0}.  This is
      * interpreted as a request for the unsatisfiably large capacity
      * {@code (long) Integer.MAX_VALUE + (minCapacity - Integer.MAX_VALUE)}.
      */
     private void ensureCapacity(int minCapacity) {
         // overflow-conscious code
         if (minCapacity - buf.length > 0)
             grow(minCapacity);
     }
 
     /**
      * The maximum size of array to allocate.
      * Some VMs reserve some header words in an array.
      * Attempts to allocate larger arrays may result in
      * OutOfMemoryError: Requested array size exceeds VM limit
      */
     private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
 
     /**
      * Increases the capacity to ensure that it can hold at least the
      * number of elements specified by the minimum capacity argument.
      *
      * @param minCapacity the desired minimum capacity
      */
     private void grow(int minCapacity) {
         // overflow-conscious code
         int oldCapacity = buf.length;
         int newCapacity = oldCapacity << 1;
         if (newCapacity - minCapacity < 0)
             newCapacity = minCapacity;
         if (newCapacity - MAX_ARRAY_SIZE > 0)
             newCapacity = hugeCapacity(minCapacity);
         buf = Arrays.copyOf(buf, newCapacity);
     }
 
     private static int hugeCapacity(int minCapacity) {
         if (minCapacity < 0) // overflow
             throw new OutOfMemoryError();
         return (minCapacity > MAX_ARRAY_SIZE) ?
             Integer.MAX_VALUE :
             MAX_ARRAY_SIZE;
     }
 
     /**
      * Writes the specified byte to this byte array output stream.
      *
      * @param   b   the byte to be written.
      */
     public synchronized void write(int b) {
         ensureCapacity(count + 1);
         buf[count] = (byte) b;
         count += 1;
     }
 
     /**
      * Writes <code>len</code> bytes from the specified byte array
      * starting at offset <code>off</code> to this byte array output stream.
      *
      * @param   b     the data.
      * @param   off   the start offset in the data.
      * @param   len   the number of bytes to write.
      */
     public synchronized void write(byte b[], int off, int len) {
         if ((off < 0) || (off > b.length) || (len < 0) ||
             ((off + len) - b.length > 0)) {
             throw new IndexOutOfBoundsException();
         }
         ensureCapacity(count + len);
         System.arraycopy(b, off, buf, count, len);
         count += len;
     }
 
     /**
      * Writes the complete contents of this byte array output stream to
      * the specified output stream argument, as if by calling the output
      * stream's write method using <code>out.write(buf, 0, count)</code>.
      *
      * @param      out   the output stream to which to write the data.
      * @exception  IOException  if an I/O error occurs.
      */
     public synchronized void writeTo(OutputStream out) throws IOException {
         out.write(buf, 0, count);
     }
 
     /**
      * Resets the <code>count</code> field of this byte array output
      * stream to zero, so that all currently accumulated output in the
      * output stream is discarded. The output stream can be used again,
      * reusing the already allocated buffer space.
      *
      * @see     java.io.ByteArrayInputStream#count
      */
     public synchronized void reset() {
         count = 0;
     }
 
     /**
      * Creates a newly allocated byte array. Its size is the current
      * size of this output stream and the valid contents of the buffer
      * have been copied into it.
      *
      * @return  the current contents of this output stream, as a byte array.
      * @see     java.io.ByteArrayOutputStream#size()
      */
     public synchronized byte toByteArray()[] {
         return Arrays.copyOf(buf, count);
     }
 
     /**
      * Returns the current size of the buffer.
      *
      * @return  the value of the <code>count</code> field, which is the number
      *          of valid bytes in this output stream.
      * @see     java.io.ByteArrayOutputStream#count
      */
     public synchronized int size() {
         return count;
     }
 
     /**
      * Converts the buffer's contents into a string decoding bytes using the
      * platform's default character set. The length of the new <tt>String</tt>
      * is a function of the character set, and hence may not be equal to the
      * size of the buffer.
      *
      * <p> This method always replaces malformed-input and unmappable-character
      * sequences with the default replacement string for the platform's
      * default character set. The {@linkplain java.nio.charset.CharsetDecoder}
      * class should be used when more control over the decoding process is
      * required.
      *
      * @return String decoded from the buffer's contents.
      * @since  JDK1.1
      */
     public synchronized String toString() {
         return new String(buf, 0, count);
     }
 
     /**
      * Converts the buffer's contents into a string by decoding the bytes using
      * the named {@link java.nio.charset.Charset charset}. The length of the new
      * <tt>String</tt> is a function of the charset, and hence may not be equal
      * to the length of the byte array.
      *
      * <p> This method always replaces malformed-input and unmappable-character
      * sequences with this charset's default replacement string. The {@link
      * java.nio.charset.CharsetDecoder} class should be used when more control
      * over the decoding process is required.
      *
      * @param      charsetName  the name of a supported
      *             {@link java.nio.charset.Charset charset}
      * @return     String decoded from the buffer's contents.
      * @exception  UnsupportedEncodingException
      *             If the named charset is not supported
      * @since      JDK1.1
      */
     public synchronized String toString(String charsetName)
         throws UnsupportedEncodingException
     {
         return new String(buf, 0, count, charsetName);
     }
 
     /**
      * Creates a newly allocated string. Its size is the current size of
      * the output stream and the valid contents of the buffer have been
      * copied into it. Each character <i>c</i> in the resulting string is
      * constructed from the corresponding element <i>b</i> in the byte
      * array such that:
      * <blockquote><pre>
      *     c == (char)(((hibyte & 0xff) << 8) | (b & 0xff))
      * </pre></blockquote>
      *
      * @deprecated This method does not properly convert bytes into characters.
      * As of JDK 1.1, the preferred way to do this is via the
      * <code>toString(String enc)</code> method, which takes an encoding-name
      * argument, or the <code>toString()</code> method, which uses the
      * platform's default character encoding.
      *
      * @param      hibyte    the high byte of each resulting Unicode character.
      * @return     the current contents of the output stream, as a string.
      * @see        java.io.ByteArrayOutputStream#size()
      * @see        java.io.ByteArrayOutputStream#toString(String)
      * @see        java.io.ByteArrayOutputStream#toString()
      */
     @Deprecated
     public synchronized String toString(int hibyte) {
         return new String(buf, hibyte, 0, count);
     }
 
     /**
      * Closing a <tt>ByteArrayOutputStream</tt> has no effect. The methods in
      * this class can be called after the stream has been closed without
      * generating an <tt>IOException</tt>.
      */
     public void close() throws IOException {
     }
 
 }
​

BufferedOutputStream

 /**
  * The class implements a buffered output stream. By setting up such
  * an output stream, an application can write bytes to the underlying
  * output stream without necessarily causing a call to the underlying
  * system for each byte written.
  *
  * @author  Arthur van Hoff
  * @since   JDK1.0
  */
 public
 class BufferedOutputStream extends FilterOutputStream {
     /**
      * The internal buffer where data is stored.
      */
     protected byte buf[];
 
     /**
      * The number of valid bytes in the buffer. This value is always
      * in the range <tt>0</tt> through <tt>buf.length</tt>; elements
      * <tt>buf[0]</tt> through <tt>buf[count-1]</tt> contain valid
      * byte data.
      */
     protected int count;
 
     /**
      * Creates a new buffered output stream to write data to the
      * specified underlying output stream.
      *
      * @param   out   the underlying output stream.
      */
     public BufferedOutputStream(OutputStream out) {
         this(out, 8192);
     }
 
     /**
      * Creates a new buffered output stream to write data to the
      * specified underlying output stream with the specified buffer
      * size.
      *
      * @param   out    the underlying output stream.
      * @param   size   the buffer size.
      * @exception IllegalArgumentException if size <= 0.
      */
     public BufferedOutputStream(OutputStream out, int size) {
         super(out);
         if (size <= 0) {
             throw new IllegalArgumentException("Buffer size <= 0");
         }
         buf = new byte[size];
     }
 
     /** Flush the internal buffer */
     private void flushBuffer() throws IOException {
         if (count > 0) {
             out.write(buf, 0, count);
             count = 0;
         }
     }
 
     /**
      * Writes the specified byte to this buffered output stream.
      *
      * @param      b   the byte to be written.
      * @exception  IOException  if an I/O error occurs.
      */
     public synchronized void write(int b) throws IOException {
         if (count >= buf.length) {
             flushBuffer();
         }
         buf[count++] = (byte)b;
     }
 
     /**
      * Writes <code>len</code> bytes from the specified byte array
      * starting at offset <code>off</code> to this buffered output stream.
      *
      * <p> Ordinarily this method stores bytes from the given array into this
      * stream's buffer, flushing the buffer to the underlying output stream as
      * needed.  If the requested length is at least as large as this stream's
      * buffer, however, then this method will flush the buffer and write the
      * bytes directly to the underlying output stream.  Thus redundant
      * <code>BufferedOutputStream</code>s will not copy data unnecessarily.
      *
      * @param      b     the data.
      * @param      off   the start offset in the data.
      * @param      len   the number of bytes to write.
      * @exception  IOException  if an I/O error occurs.
      */
     public synchronized void write(byte b[], int off, int len) throws IOException {
         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;
         }
         if (len > buf.length - count) {
             flushBuffer();
         }
         System.arraycopy(b, off, buf, count, len);
         count += len;
     }
 
     /**
      * Flushes this buffered output stream. This forces any buffered
      * output bytes to be written out to the underlying output stream.
      *
      * @exception  IOException  if an I/O error occurs.
      * @see        java.io.FilterOutputStream#out
      */
     public synchronized void flush() throws IOException {
         flushBuffer();
         out.flush();
     }
 }
​

PipedOutputStream

 /**
  * A piped output stream can be connected to a piped input stream
  * to create a communications pipe. The piped output stream is the
  * sending end of the pipe. Typically, data is written to a
  * <code>PipedOutputStream</code> object by one thread and data is
  * read from the connected <code>PipedInputStream</code> by some
  * other thread. Attempting to use both objects from a single thread
  * is not recommended as it may deadlock the thread.
  * The pipe is said to be <a name=BROKEN> <i>broken</i> </a> if a
  * thread that was reading data bytes from the connected piped input
  * stream is no longer alive.
  *
  * @author  James Gosling
  * @see     java.io.PipedInputStream
  * @since   JDK1.0
  */
 public
 class PipedOutputStream extends OutputStream {
 
         /* REMIND: identification of the read and write sides needs to be
            more sophisticated.  Either using thread groups (but what about
            pipes within a thread?) or using finalization (but it may be a
            long time until the next GC). */
     private PipedInputStream sink;
 
     /**
      * Creates a piped output stream connected to the specified piped
      * input stream. Data bytes written to this stream will then be
      * available as input from <code>snk</code>.
      *
      * @param      snk   The piped input stream to connect to.
      * @exception  IOException  if an I/O error occurs.
      */
     public PipedOutputStream(PipedInputStream snk)  throws IOException {
         connect(snk);
     }
 
     /**
      * Creates a piped output stream that is not yet connected to a
      * piped input stream. It must be connected to a piped input stream,
      * either by the receiver or the sender, before being used.
      *
      * @see     java.io.PipedInputStream#connect(java.io.PipedOutputStream)
      * @see     java.io.PipedOutputStream#connect(java.io.PipedInputStream)
      */
     public PipedOutputStream() {
     }
 
     /**
      * Connects this piped output stream to a receiver. If this object
      * is already connected to some other piped input stream, an
      * <code>IOException</code> is thrown.
      * <p>
      * If <code>snk</code> is an unconnected piped input stream and
      * <code>src</code> is an unconnected piped output stream, they may
      * be connected by either the call:
      * <blockquote><pre>
      * src.connect(snk)</pre></blockquote>
      * or the call:
      * <blockquote><pre>
      * snk.connect(src)</pre></blockquote>
      * The two calls have the same effect.
      *
      * @param      snk   the piped input stream to connect to.
      * @exception  IOException  if an I/O error occurs.
      */
     public synchronized void connect(PipedInputStream snk) throws IOException {
         if (snk == null) {
             throw new NullPointerException();
         } else if (sink != null || snk.connected) {
             throw new IOException("Already connected");
         }
         sink = snk;
         snk.in = -1;
         snk.out = 0;
         snk.connected = true;
     }
 
     /**
      * Writes the specified <code>byte</code> to the piped output stream.
      * <p>
      * Implements the <code>write</code> method of <code>OutputStream</code>.
      *
      * @param      b   the <code>byte</code> to be written.
      * @exception IOException if the pipe is <a href=#BROKEN> broken</a>,
      *          {@link #connect(java.io.PipedInputStream) unconnected},
      *          closed, or if an I/O error occurs.
      */
     public void write(int b)  throws IOException {
         if (sink == null) {
             throw new IOException("Pipe not connected");
         }
         sink.receive(b);
     }
 
     /**
      * Writes <code>len</code> bytes from the specified byte array
      * starting at offset <code>off</code> to this piped output stream.
      * This method blocks until all the bytes are written to the output
      * stream.
      *
      * @param      b     the data.
      * @param      off   the start offset in the data.
      * @param      len   the number of bytes to write.
      * @exception IOException if the pipe is <a href=#BROKEN> broken</a>,
      *          {@link #connect(java.io.PipedInputStream) unconnected},
      *          closed, or if an I/O error occurs.
      */
     public void write(byte b[], int off, int len) throws IOException {
         if (sink == null) {
             throw new IOException("Pipe not connected");
         } else if (b == null) {
             throw new NullPointerException();
         } else if ((off < 0) || (off > b.length) || (len < 0) ||
                    ((off + len) > b.length) || ((off + len) < 0)) {
             throw new IndexOutOfBoundsException();
         } else if (len == 0) {
             return;
         }
         sink.receive(b, off, len);
     }
 
     /**
      * Flushes this output stream and forces any buffered output bytes
      * to be written out.
      * This will notify any readers that bytes are waiting in the pipe.
      *
      * @exception IOException if an I/O error occurs.
      */
     public synchronized void flush() throws IOException {
         if (sink != null) {
             synchronized (sink) {
                 sink.notifyAll();
             }
         }
     }
 
     /**
      * Closes this piped output stream and releases any system resources
      * associated with this stream. This stream may no longer be used for
      * writing bytes.
      *
      * @exception  IOException  if an I/O error occurs.
      */
     public void close()  throws IOException {
         if (sink != null) {
             sink.receivedLast();
         }
     }
 }
​