Added specific token extractor for OAuth 2.0

src/main/java/org/scribe/extractors/TokenExtractor20Impl.java

@@ -0,0 +1,35 @@
+package org.scribe.extractors;
+
+import java.util.regex.*;
+
+import org.scribe.exceptions.*;
+import org.scribe.model.*;
+import org.scribe.utils.*;
+
+/**
+ * Default implementation of {@AccessTokenExtractor}. Conforms to OAuth 2.0
+ *
+ */
+public class TokenExtractor20Impl implements AccessTokenExtractor
+{
+  private static final String TOKEN_REGEX = "access_token=(\\S*?)(&(\\S*))?";
+  private static final String EMPTY_SECRET = "";
+
+  /**
+   * {@inheritDoc} 
+   */
+  public Token extract(String response)
+  {
+    Preconditions.checkEmptyString(response, "Response body is incorrect. Can't extract a token from an empty string");
+
+    Matcher matcher = Pattern.compile(TOKEN_REGEX).matcher(response);
+    if (matcher.matches())
+    {
+      String token = URLUtils.percentDecode(matcher.group(1));
+      return new Token(token, EMPTY_SECRET);
+    } else
+    {
+      throw new OAuthException("Response body is incorrect. Can't extract a token from this: '" + response + "'", null);
+    }
+  }
+}