private com.google.protobuf.SingleFieldBuilderV3<
            com.google.cloud.texttospeech.v1.SynthesisInput,
            com.google.cloud.texttospeech.v1.SynthesisInput.Builder,
            com.google.cloud.texttospeech.v1.SynthesisInputOrBuilder>
        getInputFieldBuilder() {
      if (inputBuilder_ == null) {
        inputBuilder_ =
            new com.google.protobuf.SingleFieldBuilderV3<
                com.google.cloud.texttospeech.v1.SynthesisInput,
                com.google.cloud.texttospeech.v1.SynthesisInput.Builder,
                com.google.cloud.texttospeech.v1.SynthesisInputOrBuilder>(
                getInput(), getParentForChildren(), isClean());
        input_ = null;
      }
      return inputBuilder_;
    }
<pre>
Required. The Synthesizer requires either plain text or SSML as input.
</pre>

<code>
.google.cloud.texttospeech.v1.SynthesisInput input = 1 [(.google.api.field_behavior) = REQUIRED];
</code>
java-texttospeech/proto-google-cloud-texttospeech-v1/src/main/java/com/google/cloud/texttospeech/v1/SynthesizeSpeechRequest.java