Improve performance of ObjectId#parseHexString (#1034)

JAVA-4816

Co-authored-by: Jeff Yemin <[email protected]>

Author: eonwhite

bson/src/main/org/bson/types/ObjectId.java

@@ -415,17 +415,30 @@ private Object readResolve() {
     }
 
     private static byte[] parseHexString(final String s) {
-        if (!isValid(s)) {
-            throw new IllegalArgumentException("invalid hexadecimal representation of an ObjectId: [" + s + "]");
-        }
+        notNull("hexString", s);
+        isTrueArgument("hexString has 24 characters", s.length() == 24);
 
         byte[] b = new byte[OBJECT_ID_LENGTH];
         for (int i = 0; i < b.length; i++) {
-            b[i] = (byte) Integer.parseInt(s.substring(i * 2, i * 2 + 2), 16);
+            int pos = i << 1;
+            char c1 = s.charAt(pos);
+            char c2 = s.charAt(pos + 1);
+            b[i] = (byte) ((hexCharToInt(c1) << 4) + hexCharToInt(c2));
         }
         return b;
     }
 
+    private static int hexCharToInt(final char c) {
+        if (c >= '0' && c <= '9') {
+            return c - 48;
+        } else if (c >= 'a' && c <= 'f') {
+            return c - 87;
+        } else if (c >= 'A' && c <= 'F') {
+            return c - 55;
+        }
+        throw new IllegalArgumentException("invalid hexadecimal character: [" + c + "]");
+    }
+
     private static int dateToTimestampSeconds(final Date time) {
         return (int) (time.getTime() / 1000);
     }

bson/src/test/unit/org/bson/types/ObjectIdTest.java

@@ -27,10 +27,12 @@
 import java.text.ParseException;
 import java.text.SimpleDateFormat;
 import java.util.Date;
+import java.util.Locale;
 import java.util.Random;
 
 import static org.junit.Assert.assertArrayEquals;
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertThrows;
 import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.fail;
 
@@ -142,6 +144,10 @@ public void testDateCons() {
     public void testHexStringConstructor() {
         ObjectId id = new ObjectId();
         assertEquals(id, new ObjectId(id.toHexString()));
+        assertEquals(id, new ObjectId(id.toHexString().toUpperCase(Locale.US)));
+        assertThrows(IllegalArgumentException.class, () -> new ObjectId((String) null));
+        assertThrows(IllegalArgumentException.class, () -> new ObjectId(id.toHexString().substring(0, 23)));
+        assertThrows(IllegalArgumentException.class, () -> new ObjectId(id.toHexString().substring(0, 23) + '%'));
     }
 
     @Test