HADOOP-7009. MD5Hash provides a public factory method that creates an instance of MessageDigest. Contributed by Hairong Kuang.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1028427 13f79535-47bb-0310-9956-ffa450edef68

CHANGES.txt

@@ -152,6 +152,9 @@ Trunk (unreleased changes)
 
     HADOOP-7010. Typo in FileSystem.java. (Jingguo Yao via eli)
 
+    HADOOP-7009. MD5Hash provides a public factory method that creates an
+    instance of thread local MessageDigest. (hairong)
+
   OPTIMIZATIONS
 
     HADOOP-6884. Add LOG.isDebugEnabled() guard for each LOG.debug(..).

src/java/org/apache/hadoop/io/MD5Hash.java

@@ -94,11 +94,18 @@ public class MD5Hash implements WritableComparable<MD5Hash> {
     return digest(data, 0, data.length);
   }
 
+  /**
+   * Create a thread local MD5 digester
+   */
+  public static MessageDigest getDigester() {
+    return DIGESTER_FACTORY.get();
+  }
+
   /** Construct a hash value for the content from the InputStream. */
   public static MD5Hash digest(InputStream in) throws IOException {
     final byte[] buffer = new byte[4*1024]; 
 
-    final MessageDigest digester = DIGESTER_FACTORY.get();
+    final MessageDigest digester = getDigester();
     for(int n; (n = in.read(buffer)) != -1; ) {
       digester.update(buffer, 0, n);
     }
@@ -109,7 +116,7 @@ public class MD5Hash implements WritableComparable<MD5Hash> {
   /** Construct a hash value for a byte array. */
   public static MD5Hash digest(byte[] data, int start, int len) {
     byte[] digest;
-    MessageDigest digester = DIGESTER_FACTORY.get();
+    MessageDigest digester = getDigester();
     digester.update(data, start, len);
     digest = digester.digest();
     return new MD5Hash(digest);