@java.lang.Override
  public com.google.cloud.vertexai.api.Retrieval getRetrieval() {
    return retrieval_ == null
        ? com.google.cloud.vertexai.api.Retrieval.getDefaultInstance()
        : retrieval_;
  }
<pre>
Optional. Retrieval tool type.
System will always execute the provided retrieval tool(s) to get external
knowledge to answer the prompt. Retrieval results are presented to the
model for generation.
</pre>

<code>
.google.cloud.vertexai.v1.Retrieval retrieval = 2 [(.google.api.field_behavior) = OPTIONAL];
</code>

@return The retrieval.
java-vertexai/proto-google-cloud-vertexai-v1/src/main/java/com/google/cloud/vertexai/api/Tool.java