public String getMessageGroupId() {
        return this.messageGroupId;
    }
<p>
This parameter applies only to FIFO (first-in-first-out) topics.
</p>
<p>
The tag that specifies that a message belongs to a specific message group. Messages that belong to the same
message group are processed in a FIFO manner (however, messages in different message groups might be processed
out of order). To interleave multiple ordered streams within a single topic, use <code>MessageGroupId</code>
values (for example, session data for multiple users). In this scenario, multiple consumers can process the
topic, but the session data of each user is processed in a FIFO fashion.
</p>
<p>
You must associate a non-empty <code>MessageGroupId</code> with a message. If you don't provide a
<code>MessageGroupId</code>, the action fails.
</p>
<p>
The length of <code>MessageGroupId</code> is 128 characters.
</p>
<p>
<code>MessageGroupId</code> can contain alphanumeric characters <code>(a-z, A-Z, 0-9)</code> and punctuation
<code>(!"#$%&amp;'()*+,-./:;&lt;=&gt;?@[\]^_`{|}~)</code>.
</p>
<important>
<p>
<code>MessageGroupId</code> is required for FIFO topics. You can't use it for standard topics.
</p>
</important>

@return This parameter applies only to FIFO (first-in-first-out) topics.</p>
        <p>
        The tag that specifies that a message belongs to a specific message group. Messages that belong to the
        same message group are processed in a FIFO manner (however, messages in different message groups might be
        processed out of order). To interleave multiple ordered streams within a single topic, use
        <code>MessageGroupId</code> values (for example, session data for multiple users). In this scenario,
        multiple consumers can process the topic, but the session data of each user is processed in a FIFO
        fashion.
        </p>
        <p>
        You must associate a non-empty <code>MessageGroupId</code> with a message. If you don't provide a
        <code>MessageGroupId</code>, the action fails.
        </p>
        <p>
        The length of <code>MessageGroupId</code> is 128 characters.
        </p>
        <p>
        <code>MessageGroupId</code> can contain alphanumeric characters <code>(a-z, A-Z, 0-9)</code> and
        punctuation <code>(!"#$%&amp;'()*+,-./:;&lt;=&gt;?@[\]^_`{|}~)</code>.
        </p>
        <important>
        <p>
        <code>MessageGroupId</code> is required for FIFO topics. You can't use it for standard topics.
        </p>
aws-java-sdk-sns/src/main/java/com/amazonaws/services/sns/model/PublishBatchRequestEntry.java