Multipart performs blocking call in every instantiation #699

api/src/main/java/jakarta/mail/Message.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1997, 2023 Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 2024 Oracle and/or its affiliates. All rights reserved.
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Public License v. 2.0, which is available at
@@ -17,11 +17,13 @@
 package jakarta.mail;
 
 import jakarta.mail.search.SearchTerm;
+import jakarta.mail.util.StreamProvider;
 
 import java.io.InvalidObjectException;
 import java.io.ObjectStreamException;
 import java.io.Serializable;
 import java.util.Date;
+import java.util.ServiceConfigurationError;
 
 /**
  * This class models an email message. This is an abstract class.
@@ -705,4 +707,33 @@ protected void setExpunged(boolean expunged) {
     public boolean match(SearchTerm term) throws MessagingException {
         return term.match(this);
     }
+
+    /**
+     * Obtains the {@link StreamProvider} from the session, if exists.
+     * Otherwise it obtains it from
+     * {@link Session#getDefaultInstance(java.util.Properties, Authenticator)}.
+     *
+     * @return the StreamProvider implementation from the session.
+     * @throws MessagingException if errors.
+     *
+     * @since JavaMail 2.2
+     */
+    protected StreamProvider provider() throws MessagingException {
+        try {
+            try {
+                final Session s = this.session;
+                if (s != null) {
+                    return s.getStreamProvider();
+                } else {
+                    return Session.getDefaultInstance(System.getProperties(),
+                        null).getStreamProvider();
+                }
+            } catch (ServiceConfigurationError sce) {
+                throw new IllegalStateException(sce);
+            }
+        } catch (RuntimeException re) {
+            throw new MessagingException("Unable to get "
+                    + StreamProvider.class.getName(), re);
+        }
+    }
 }

api/src/main/java/jakarta/mail/Multipart.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1997, 2023 Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 2024 Oracle and/or its affiliates. All rights reserved.
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Public License v. 2.0, which is available at
@@ -21,6 +21,8 @@
 import java.io.IOException;
 import java.io.OutputStream;
 import java.util.Vector;
+import java.util.logging.Level;
+import java.util.logging.Logger;
 
 /**
  * Multipart is a container that holds multiple body parts. Multipart
@@ -42,6 +44,7 @@
 
 public abstract class Multipart {
 
+    private static final Logger LOGGER = Logger.getLogger(Multipart.class.getName());
     /**
      * Vector of BodyPart objects.
      */
@@ -64,9 +67,9 @@ public abstract class Multipart {
     /**
      * Instance of stream provider.
      *
-     * @since JavaMail 2.1
+     * @since JavaMail 2.2
      */
-    protected final StreamProvider streamProvider = StreamProvider.provider();
+    private volatile StreamProvider streamProvider;
 
     /**
      * Default constructor. An empty Multipart object is created.
@@ -266,4 +269,27 @@ public synchronized Part getParent() {
     public synchronized void setParent(Part parent) {
         this.parent = parent;
     }
+
+    protected StreamProvider provider() {
+        if (streamProvider == null) {
+            synchronized (this) {
+                if (streamProvider == null) {
+                    if (parent != null && parent instanceof Message) {
+                        try {
+                            streamProvider = ((Message)parent).provider();
+                        } catch (MessagingException e) {
+                            if (LOGGER.isLoggable(Level.FINE)) {
+                                LOGGER.log(Level.FINE, "Cannot reuse streamProvider", e);
+                            }
+                        }
+                    }
+                }
+                if (streamProvider == null) {
+                    streamProvider = StreamProvider.provider();
+                }
+            }
+        }
+        return streamProvider;
+    }
+
 }

api/src/main/java/jakarta/mail/internet/MimeMessage.java

@@ -2322,23 +2322,4 @@ protected MimeMessage createMimeMessage(Session session)
             throws MessagingException {
         return new MimeMessage(session);
     }
-
-    private StreamProvider provider() throws MessagingException {
-        try {
-            try {
-                final Session s = this.session;
-                if (s != null) {
-                    return s.getStreamProvider();
-                } else {
-                    return Session.getDefaultInstance(System.getProperties(),
-                        null).getStreamProvider();
-                }
-            } catch (ServiceConfigurationError sce) {
-                throw new IllegalStateException(sce);
-            }
-        } catch (RuntimeException re) {
-            throw new MessagingException("Unable to get "
-                    + StreamProvider.class.getName(), re);
-        }
-    }
 }

api/src/main/java/jakarta/mail/internet/MimeMultipart.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1997, 2023 Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 2024 Oracle and/or its affiliates. All rights reserved.
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Public License v. 2.0, which is available at
@@ -520,7 +520,7 @@ public synchronized void writeTo(OutputStream os)
 
         String boundary = "--" +
                 (new ContentType(contentType)).getParameter("boundary");
-        LineOutputStream los = streamProvider.outputLineStream(os, false);
+        LineOutputStream los = provider().outputLineStream(os, false);
         // if there's a preamble, write it out
         if (preamble != null) {
             byte[] pb = MimeUtility.getBytes(preamble);
@@ -601,7 +601,7 @@ protected synchronized void parse() throws MessagingException {
 
         try {
             // Skip and save the preamble
-            LineInputStream lin = streamProvider.inputLineStream(in, false);
+            LineInputStream lin = provider().inputLineStream(in, false);
             StringBuilder preamblesb = null;
             String line;
             while ((line = lin.readLine()) != null) {