docs: Add an example for ClientOptions usage

examples/src/main/java/com/google/genai/examples/GenerateContentWithClientOptions.java

@@ -0,0 +1,85 @@
+/*
+ * Copyright 2025 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * Usage:
+ *
+ * <p>1a. If you are using Vertex AI, setup ADC to get credentials:
+ * https://cloud.google.com/docs/authentication/provide-credentials-adc#google-idp
+ *
+ * <p>Then set Project, Location, and USE_VERTEXAI flag as environment variables:
+ *
+ * <p>export GOOGLE_CLOUD_PROJECT=YOUR_PROJECT
+ *
+ * <p>export GOOGLE_CLOUD_LOCATION=YOUR_LOCATION
+ *
+ * <p>export GOOGLE_GENAI_USE_VERTEXAI=true
+ *
+ * <p>1b. If you are using Gemini Developer API, set an API key environment variable. You can find a
+ * list of available API keys here: https://aistudio.google.com/app/apikey
+ *
+ * <p>export GOOGLE_API_KEY=YOUR_API_KEY
+ *
+ * <p>2. Compile the java package and run the sample code.
+ *
+ * <p>mvn clean compile
+ *
+ * <p>mvn exec:java -Dexec.mainClass="com.google.genai.examples.GenerateContentWithClientOptions"
+ * -Dexec.args="YOUR_MODEL_ID"
+ */
+package com.google.genai.examples;
+
+import com.google.genai.Client;
+import com.google.genai.types.ClientOptions;
+import com.google.genai.types.GenerateContentResponse;
+import com.google.genai.types.ProxyOptions;
+import com.google.genai.types.ProxyType;
+
+/** An example of setting client options in a GenerateContent request. */
+public final class GenerateContentWithClientOptions {
+  public static void main(String[] args) {
+    final String modelId;
+    if (args.length != 0) {
+      modelId = args[0];
+    } else {
+      modelId = Constants.GEMINI_MODEL_NAME;
+    }
+
+    // Set the client options when creating the client. This applies to all requests made through
+    // this client.
+    ClientOptions clientOptions =
+        ClientOptions.builder()
+            .proxyOptions(ProxyOptions.builder().type(ProxyType.Known.DIRECT))
+            .maxConnections(10)
+            .maxConnectionsPerHost(5)
+            .build();
+
+    Client client = Client.builder().clientOptions(clientOptions).build();
+
+    if (client.vertexAI()) {
+      System.out.println("Using Vertex AI");
+    } else {
+      System.out.println("Using Gemini Developer API");
+    }
+
+    GenerateContentResponse response =
+        client.models.generateContent(modelId, "Tell me the history of LLM in 100 words", null);
+
+    System.out.println("Response: " + response.text());
+  }
+
+  private GenerateContentWithClientOptions() {}
+}