content: /*
   * Copyright (c) 1994, 2011, Oracle and/or its affiliates. All rights reserved.
   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   *
   * This code is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License version 2 only, as
   * published by the Free Software Foundation.  Oracle designates this
   * particular file as subject to the "Classpath" exception as provided
   * by Oracle in the LICENSE file that accompanied this code.
   *
   * This code is distributed in the hope that it will be useful, but WITHOUT
   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   * version 2 for more details (a copy is included in the LICENSE file that
   * accompanied this code).
   *
   * You should have received a copy of the GNU General Public License version
   * 2 along with this work; if not, write to the Free Software Foundation,
   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   *
   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
   * or visit www.oracle.com if you need additional information or have any
   * questions.
   */
  
  package java.io;
  
  import java.io.InputStream;
  import java.util.Enumeration;
  import java.util.Vector;
  
  /**
   * A <code>SequenceInputStream</code> represents
   * the logical concatenation of other input
   * streams. It starts out with an ordered
   * collection of input streams and reads from
   * the first one until end of file is reached,
   * whereupon it reads from the second one,
   * and so on, until end of file is reached
   * on the last of the contained input streams.
   *
   * @author  Author van Hoff
   * @since   JDK1.0
   */
  public
  class SequenceInputStream extends InputStream {
      Enumeration<? extends InputStream> e;
      InputStream in;
  
      /**
       * Initializes a newly created <code>SequenceInputStream</code>
       * by remembering the argument, which must
       * be an <code>Enumeration</code>  that produces
       * objects whose run-time type is <code>InputStream</code>.
       * The input streams that are  produced by
       * the enumeration will be read, in order,
       * to provide the bytes to be read  from this
       * <code>SequenceInputStream</code>. After
       * each input stream from the enumeration
       * is exhausted, it is closed by calling its
       * <code>close</code> method.
       *
       * @param   e   an enumeration of input streams.
       * @see     Enumeration
       */
      public SequenceInputStream(Enumeration<? extends InputStream> e) {
          this.e = e;
          try {
              nextStream();
          } catch (IOException ex) {
              // This should never happen
              throw new Error("panic");
          }
      }
  
      /**
       * Initializes a newly
       * created <code>SequenceInputStream</code>
       * by remembering the two arguments, which
       * will be read in order, first <code>s1</code>
       * and then <code>s2</code>, to provide the
       * bytes to be read from this <code>SequenceInputStream</code>.
       *
       * @param   s1   the first input stream to read.
       * @param   s2   the second input stream to read.
       */
      public SequenceInputStream(InputStream s1, InputStream s2) {
          Vector<InputStream> v = new Vector<>(2);
  
          v.addElement(s1);
          v.addElement(s2);
          e = v.elements();
          try {
              nextStream();
          } catch (IOException ex) {
              // This should never happen
              throw new Error("panic");
          }
      }
  
      /**
       *  Continues reading in the next stream if an EOF is reached.
       */
      final void nextStream() throws IOException {
          if (in != null) {
              in.close();
          }
  
          if (e.hasMoreElements()) {
              in = (InputStream) e.nextElement();
              if (in == null)
                  throw new NullPointerException();
          }
          else in = null;
  
      }
  
      /**
       * Returns an estimate of the number of bytes that can be read (or
       * skipped over) from the current underlying input stream without
       * blocking by the next invocation of a method for the current
       * underlying 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 simply calls {@code available} of the current underlying
       * input stream and returns the result.
       *
       * @return an estimate of the number of bytes that can be read (or
       *         skipped over) from the current underlying input stream
       *         without blocking or {@code 0} if this input stream
       *         has been closed by invoking its {@link #close()} method
       * @exception  IOException  if an I/O error occurs.
       *
       * @since   JDK1.1
       */
      public int available() throws IOException {
          if (in == null) {
              return 0; // no way to signal EOF from available()
          }
          return in.available();
      }
  
      /**
       * Reads the next byte of data from this input stream. The byte is
       * returned as an <code>int</code> in the range <code>0</code> to
       * <code>255</code>. If no byte is available because the end of the
       * stream has been reached, the value <code>-1</code> is returned.
       * This method blocks until input data is available, the end of the
       * stream is detected, or an exception is thrown.
       * <p>
       * This method
       * tries to read one character from the current substream. If it
       * reaches the end of the stream, it calls the <code>close</code>
       * method of the current substream and begins reading from the next
       * substream.
       *
       * @return     the next byte of data, or <code>-1</code> if the end of the
       *             stream is reached.
       * @exception  IOException  if an I/O error occurs.
       */
      public int read() throws IOException {
          while (in != null) {
              int c = in.read();
              if (c != -1) {
                  return c;
              }
              nextStream();
          }
          return -1;
      }
  
      /**
       * Reads up to <code>len</code> bytes of data from this input stream
       * into an array of bytes.  If <code>len</code> is not zero, the method
       * blocks until at least 1 byte of input is available; otherwise, no
       * bytes are read and <code>0</code> is returned.
       * <p>
       * The <code>read</code> method of <code>SequenceInputStream</code>
       * tries to read the data from the current substream. If it fails to
       * read any characters because the substream has reached the end of
       * the stream, it calls the <code>close</code> method of the current
       * substream and begins reading from the next substream.
       *
       * @param      b     the buffer into which the data is read.
       * @param      off   the start offset in array <code>b</code>
       *                   at which the data is written.
       * @param      len   the maximum number of bytes read.
       * @return     int   the number of bytes read.
       * @exception  NullPointerException If <code>b</code> is <code>null</code>.
       * @exception  IndexOutOfBoundsException If <code>off</code> is negative,
       * <code>len</code> is negative, or <code>len</code> is greater than
       * <code>b.length - off</code>
       * @exception  IOException  if an I/O error occurs.
       */
      public int read(byte b[], int off, int len) throws IOException {
          if (in == null) {
              return -1;
          } else if (b == null) {
              throw new NullPointerException();
          } else if (off < 0 || len < 0 || len > b.length - off) {
              throw new IndexOutOfBoundsException();
          } else if (len == 0) {
              return 0;
          }
          do {
              int n = in.read(b, off, len);
              if (n > 0) {
                  return n;
              }
              nextStream();
          } while (in != null);
          return -1;
      }
  
      /**
       * Closes this input stream and releases any system resources
       * associated with the stream.
       * A closed <code>SequenceInputStream</code>
       * cannot  perform input operations and cannot
       * be reopened.
       * <p>
       * If this stream was created
       * from an enumeration, all remaining elements
       * are requested from the enumeration and closed
       * before the <code>close</code> method returns.
       *
       * @exception  IOException  if an I/O error occurs.
       */
      public void close() throws IOException {
          do {
              nextStream();
          } while (in != null);
      }
  }
  