org.spearce.jgit/src/org/spearce/jgit/lib/ObjectLoader.java

   1 /*
   2  *  Copyright (C) 2006  Shawn Pearce <spearce@spearce.org>
   3  *
   4  *  This library is free software; you can redistribute it and/or
   5  *  modify it under the terms of the GNU General Public
   6  *  License, version 2, as published by the Free Software Foundation.
   7  *
   8  *  This library is distributed in the hope that it will be useful,
   9  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  10  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  11  *  General Public License for more details.
  12  *
  13  *  You should have received a copy of the GNU General Public
  14  *  License along with this library; if not, write to the Free Software
  15  *  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301
  16  */
  17 package org.spearce.jgit.lib;
  18
  19 import java.io.IOException;
  20 import java.security.MessageDigest;
  21
  22 /**
  23  * Base class for a set of loaders for different representations of Git objects.
  24  * New loaders are constructed for every object.
  25  */
  26 public abstract class ObjectLoader {
  27         private ObjectId objectId;
  28
  29         /**
  30          * @return the id of this object, possibly computed on demand
  31          * @throws IOException
  32          */
  33         public ObjectId getId() throws IOException {
  34                 if (objectId == null) {
  35                         final MessageDigest md = Constants.newMessageDigest();
  36                         md.update(Constants.encodedTypeString(getType()));
  37                         md.update((byte) ' ');
  38                         md.update(Constants.encodeASCII(getSize()));
  39                         md.update((byte) 0);
  40                         md.update(getCachedBytes());
  41                         objectId = ObjectId.fromRaw(md.digest());
  42                 }
  43                 return objectId;
  44         }
  45
  46         /**
  47          * Set the SHA-1 id of the object handled by this loader
  48          *
  49          * @param id
  50          */
  51         protected void setId(final ObjectId id) {
  52                 if (objectId != null)
  53                         throw new IllegalStateException("Id already set.");
  54                 objectId = id;
  55         }
  56
  57         /**
  58          * @return Git in pack object type, see {@link Constants}.
  59          * @throws IOException
  60          */
  61         public abstract int getType() throws IOException;
  62
  63         /**
  64          * @return size of object in bytes
  65          * @throws IOException
  66          */
  67         public abstract long getSize() throws IOException;
  68
  69         /**
  70          * Obtain a copy of the bytes of this object.
  71          * <p>
  72          * Unlike {@link #getCachedBytes()} this method returns an array that might
  73          * be modified by the caller.
  74          *
  75          * @return the bytes of this object.
  76          * @throws IOException
  77          *             the object cannot be read.
  78          */
  79         public abstract byte[] getBytes() throws IOException;
  80
  81         /**
  82          * Obtain a reference to the (possibly cached) bytes of this object.
  83          * <p>
  84          * This method offers direct access to the internal caches, potentially
  85          * saving on data copies between the internal cache and higher level code.
  86          * Callers who receive this reference <b>must not</b> modify its contents.
  87          * Changes (if made) will affect the cache but not the repository itself.
  88          *
  89          * @return the cached bytes of this object. Do not modify it.
  90          * @throws IOException
  91          *             the object cannot be read.
  92          */
  93         public abstract byte[] getCachedBytes() throws IOException;
  94 }