public String getMessageStructure() {
        return this.messageStructure;
    }
<p>
Set <code>MessageStructure</code> to <code>json</code> if you want to send a different message for each protocol.
For example, using one publish action, you can send a short message to your SMS subscribers and a longer message
to your email subscribers. If you set <code>MessageStructure</code> to <code>json</code>, the value of the
<code>Message</code> parameter must:
</p>
<ul>
<li>
<p>
be a syntactically valid JSON object; and
</p>
</li>
<li>
<p>
contain at least a top-level JSON key of "default" with a value that is a string.
</p>
</li>
</ul>
<p>
You can define other top-level keys that define the message you want to send to a specific transport protocol
(e.g. http).
</p>

@return Set <code>MessageStructure</code> to <code>json</code> if you want to send a different message for each
        protocol. For example, using one publish action, you can send a short message to your SMS subscribers and
        a longer message to your email subscribers. If you set <code>MessageStructure</code> to <code>json</code>
        , the value of the <code>Message</code> parameter must: </p>
        <ul>
        <li>
        <p>
        be a syntactically valid JSON object; and
        </p>
        </li>
        <li>
        <p>
        contain at least a top-level JSON key of "default" with a value that is a string.
        </p>
        </li>
        </ul>
        <p>
        You can define other top-level keys that define the message you want to send to a specific transport
        protocol (e.g. http).
aws-java-sdk-sns/src/main/java/com/amazonaws/services/sns/model/PublishBatchRequestEntry.java