public String getIdentifier() {
        return this.identifier;
    }
<p>
An immutable identifier for a data source that is unique for an Amazon Web Services Region. Performance Insights
gathers metrics from this data source. To use a DB instance as a data source, specify its
<code>DbiResourceId</code> value. For example, specify <code>db-ABCDEFGHIJKLMNOPQRSTU1VW2X</code>.
</p>

@return An immutable identifier for a data source that is unique for an Amazon Web Services Region. Performance
        Insights gathers metrics from this data source. To use a DB instance as a data source, specify its
        <code>DbiResourceId</code> value. For example, specify <code>db-ABCDEFGHIJKLMNOPQRSTU1VW2X</code>.
aws-java-sdk-pi/src/main/java/com/amazonaws/services/pi/model/GetResourceMetadataRequest.java