MemoryCacheImageInputStream and
+ * MemoryCacheImageOutputStream.
+ * This class keeps an ArrayList of 8K blocks,
+ * loaded sequentially. Blocks may only be disposed of
+ * from the index 0 forward. As blocks are freed, the
+ * corresponding entries in the array list are set to
+ * null, but no compacting is performed.
+ * This allows the index for each block to never change,
+ * and the length of the cache is always the same as the
+ * total amount of data ever cached. Cached data is
+ * therefore always contiguous from the point of last
+ * disposal to the current length.
+ *
+ * The total number of blocks resident in the cache must not
+ * exceed Integer.MAX_VALUE. In practice, the limit of
+ * available memory will be exceeded long before this becomes an
+ * issue, since a full cache would contain 8192*2^31 = 16 terabytes of
+ * data.
+ *
+ * A MemoryCache may be reused after a call
+ * to reset().
+ */
+class MemoryCache {
+
+ private static final int BUFFER_LENGTH = 8192;
+
+ private ArrayListpos bytes are cached,
+ * or the end of the source is reached. The return value
+ * is equal to the smaller of pos and the
+ * length of the source.
+ */
+ public long loadFromStream(InputStream stream, long pos)
+ throws IOException {
+ // We've already got enough data cached
+ if (pos < length) {
+ return pos;
+ }
+
+ int offset = (int)(length % BUFFER_LENGTH);
+ byte [] buf = null;
+
+ long len = pos - length;
+ if (offset != 0) {
+ buf = getCacheBlock(length/BUFFER_LENGTH);
+ }
+
+ while (len > 0) {
+ if (buf == null) {
+ try {
+ buf = new byte[BUFFER_LENGTH];
+ } catch (OutOfMemoryError e) {
+ throw new IOException("No memory left for cache!");
+ }
+ offset = 0;
+ }
+
+ int left = BUFFER_LENGTH - offset;
+ int nbytes = (int)Math.min(len, (long)left);
+ nbytes = stream.read(buf, offset, nbytes);
+ if (nbytes == -1) {
+ return length; // EOF
+ }
+
+ if (offset == 0) {
+ cache.add(buf);
+ }
+
+ len -= nbytes;
+ length += nbytes;
+ offset += nbytes;
+
+ if (offset >= BUFFER_LENGTH) {
+ // we've filled the current buffer, so a new one will be
+ // allocated next time around (and offset will be reset to 0)
+ buf = null;
+ }
+ }
+
+ return pos;
+ }
+
+ /**
+ * Writes out a portion of the cache to an OutputStream.
+ * This method preserves no state about the output stream, and does
+ * not dispose of any blocks containing bytes written. To dispose
+ * blocks, use {@link #disposeBefore disposeBefore()}.
+ *
+ * @exception IndexOutOfBoundsException if any portion of
+ * the requested data is not in the cache (including if pos
+ * is in a block already disposed), or if either pos or
+ * len is < 0.
+ */
+ public void writeToStream(OutputStream stream, long pos, long len)
+ throws IOException {
+ if (pos + len > length) {
+ throw new IndexOutOfBoundsException("Argument out of cache");
+ }
+ if ((pos < 0) || (len < 0)) {
+ throw new IndexOutOfBoundsException("Negative pos or len");
+ }
+ if (len == 0) {
+ return;
+ }
+
+ long bufIndex = pos/BUFFER_LENGTH;
+ if (bufIndex < cacheStart) {
+ throw new IndexOutOfBoundsException("pos already disposed");
+ }
+ int offset = (int)(pos % BUFFER_LENGTH);
+
+ byte[] buf = getCacheBlock(bufIndex++);
+ while (len > 0) {
+ if (buf == null) {
+ buf = getCacheBlock(bufIndex++);
+ offset = 0;
+ }
+ int nbytes = (int)Math.min(len, (long)(BUFFER_LENGTH - offset));
+ stream.write(buf, offset, nbytes);
+ buf = null;
+ len -= nbytes;
+ }
+ }
+
+ /**
+ * Ensure that there is space to write a byte at the given position.
+ */
+ private void pad(long pos) throws IOException {
+ long currIndex = cacheStart + cache.size() - 1;
+ long lastIndex = pos/BUFFER_LENGTH;
+ long numNewBuffers = lastIndex - currIndex;
+ for (long i = 0; i < numNewBuffers; i++) {
+ try {
+ cache.add(new byte[BUFFER_LENGTH]);
+ } catch (OutOfMemoryError e) {
+ throw new IOException("No memory left for cache!");
+ }
+ }
+ }
+
+ /**
+ * Overwrites and/or appends the cache from a byte array.
+ * The length of the cache will be extended as needed to hold
+ * the incoming data.
+ *
+ * @param b an array of bytes containing data to be written.
+ * @param off the starting offset withing the data array.
+ * @param len the number of bytes to be written.
+ * @param pos the cache position at which to begin writing.
+ *
+ * @exception NullPointerException if b is null.
+ * @exception IndexOutOfBoundsException if off,
+ * len, or pos are negative,
+ * or if off+len > b.length.
+ */
+ public void write(byte[] b, int off, int len, long pos)
+ throws IOException {
+ if (b == null) {
+ throw new NullPointerException("b == null!");
+ }
+ // Fix 4430357 - if off + len < 0, overflow occurred
+ if ((off < 0) || (len < 0) || (pos < 0) ||
+ (off + len > b.length) || (off + len < 0)) {
+ throw new IndexOutOfBoundsException();
+ }
+
+ // Ensure there is space for the incoming data
+ long lastPos = pos + len - 1;
+ if (lastPos >= length) {
+ pad(lastPos);
+ length = lastPos + 1;
+ }
+
+ // Copy the data into the cache, block by block
+ int offset = (int)(pos % BUFFER_LENGTH);
+ while (len > 0) {
+ byte[] buf = getCacheBlock(pos/BUFFER_LENGTH);
+ int nbytes = Math.min(len, BUFFER_LENGTH - offset);
+ System.arraycopy(b, off, buf, offset, nbytes);
+
+ pos += nbytes;
+ off += nbytes;
+ len -= nbytes;
+ offset = 0; // Always after the first time
+ }
+ }
+
+ /**
+ * Overwrites or appends a single byte to the cache.
+ * The length of the cache will be extended as needed to hold
+ * the incoming data.
+ *
+ * @param b an int whose 8 least significant bits
+ * will be written.
+ * @param pos the cache position at which to begin writing.
+ *
+ * @exception IndexOutOfBoundsException if pos is negative.
+ */
+ public void write(int b, long pos) throws IOException {
+ if (pos < 0) {
+ throw new ArrayIndexOutOfBoundsException("pos < 0");
+ }
+
+ // Ensure there is space for the incoming data
+ if (pos >= length) {
+ pad(pos);
+ length = pos + 1;
+ }
+
+ // Insert the data.
+ byte[] buf = getCacheBlock(pos/BUFFER_LENGTH);
+ int offset = (int)(pos % BUFFER_LENGTH);
+ buf[offset] = (byte)b;
+ }
+
+ /**
+ * Returns the total length of data that has been cached,
+ * regardless of whether any early blocks have been disposed.
+ * This value will only ever increase.
+ */
+ public long getLength() {
+ return length;
+ }
+
+ /**
+ * Returns the single byte at the given position, as an
+ * int. Returns -1 if this position has
+ * not been cached or has been disposed.
+ */
+ public int read(long pos) throws IOException {
+ if (pos >= length) {
+ return -1;
+ }
+
+ byte[] buf = getCacheBlock(pos/BUFFER_LENGTH);
+ if (buf == null) {
+ return -1;
+ }
+
+ return buf[(int)(pos % BUFFER_LENGTH)] & 0xff;
+ }
+
+ /**
+ * Copy len bytes from the cache, starting
+ * at cache position pos, into the array
+ * b at offset off.
+ *
+ * @exception NullPointerException if b is null
+ * @exception IndexOutOfBoundsException if off,
+ * len or pos are negative or if
+ * off + len > b.length or if any portion of the
+ * requested data is not in the cache (including if
+ * pos is in a block that has already been disposed).
+ */
+ public void read(byte[] b, int off, int len, long pos)
+ throws IOException {
+ if (b == null) {
+ throw new NullPointerException("b == null!");
+ }
+ // Fix 4430357 - if off + len < 0, overflow occurred
+ if ((off < 0) || (len < 0) || (pos < 0) ||
+ (off + len > b.length) || (off + len < 0)) {
+ throw new IndexOutOfBoundsException();
+ }
+ if (pos + len > length) {
+ throw new IndexOutOfBoundsException();
+ }
+
+ long index = pos/BUFFER_LENGTH;
+ int offset = (int)pos % BUFFER_LENGTH;
+ while (len > 0) {
+ int nbytes = Math.min(len, BUFFER_LENGTH - offset);
+ byte[] buf = getCacheBlock(index++);
+ System.arraycopy(buf, offset, b, off, nbytes);
+
+ len -= nbytes;
+ off += nbytes;
+ offset = 0; // Always after the first time
+ }
+ }
+
+ /**
+ * Free the blocks up to the position pos.
+ * The byte at pos remains available.
+ *
+ * @exception IndexOutOfBoundsException if pos
+ * is in a block that has already been disposed.
+ */
+ public void disposeBefore(long pos) {
+ long index = pos/BUFFER_LENGTH;
+ if (index < cacheStart) {
+ throw new IndexOutOfBoundsException("pos already disposed");
+ }
+ long numBlocks = Math.min(index - cacheStart, cache.size());
+ for (long i = 0; i < numBlocks; i++) {
+ cache.remove(0);
+ }
+ this.cacheStart = index;
+ }
+
+ /**
+ * Erase the entire cache contents and reset the length to 0.
+ * The cache object may subsequently be reused as though it had just
+ * been allocated.
+ */
+ public void reset() {
+ cache.clear();
+ cacheStart = 0;
+ length = 0L;
+ }
+ }