#131: implements EncodingAware

Author: bbottema

src/main/java/org/simplejavamail/converter/internal/mimemessage/NamedDataSource.java

@@ -1,6 +1,7 @@
 package org.simplejavamail.converter.internal.mimemessage;
 
 import javax.activation.DataSource;
+import javax.mail.EncodingAware;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
@@ -10,7 +11,7 @@
 /**
  * Allows given datasource to be renamed (from {@link javax.activation.DataHandler} perspective).
  */
-class NamedDataSource implements DataSource {
+class NamedDataSource implements DataSource, EncodingAware {
 
 	/**
 	 * Original data source used for attachment.
@@ -69,4 +70,15 @@ public String getContentType() {
 	public String getName() {
 		return !valueNullOrEmpty(name) ? name : dataSource.getName();
 	}
+	
+	/**
+	 * Optimization to help Java Mail determine encoding for attachments.
+	 *
+	 * @return The encoding from the nested data source if it implements {@link EncodingAware} as well.
+	 * @see <a href="https://github.com/bbottema/simple-java-mail/issues/131">Bug report #131</a>
+	 */
+	@Override
+	public String getEncoding() {
+		return (this.dataSource instanceof EncodingAware) ? ((EncodingAware) this.dataSource).getEncoding() : null;
+	}
 }