Add azure kafka function sample

- Add sample project with Azure KafkaTrigger and Output Kakfa Bindings
 - Add README docs

 Resolves #836

spring-cloud-function-samples/function-sample-azure-kafka-trigger/src/main/java/example/KafkaTriggerDemoApplication.java

@@ -0,0 +1,61 @@
+/*
+ * Copyright 2022 the original author or authors.
+ *
+ * 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.
+ */
+package example;
+
+import java.util.Map;
+import java.util.function.Function;
+
+import com.microsoft.azure.functions.ExecutionContext;
+import example.entity.KafkaEntity;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.cloud.function.json.JsonMapper;
+import org.springframework.context.annotation.Bean;
+import org.springframework.messaging.Message;
+
+@SpringBootApplication
+public class KafkaTriggerDemoApplication {
+
+	public static void main(String[] args) {
+		SpringApplication.run(KafkaTriggerDemoApplication.class, args);
+	}
+
+	@Bean
+	public Function<Message<String>, String> uppercase(JsonMapper mapper) {
+		return message -> {
+
+			// // (Optionally) access and use the Azure function context.
+			ExecutionContext context = (ExecutionContext) message.getHeaders().get("executionContext");
+			context.getLogger().info("Kafka triggered with data: " + message.getPayload());
+
+			// Convert the message payload into Azure's KafkaEntity format.
+			KafkaEntity kafkaEntity = mapper.fromJson(message.getPayload(), KafkaEntity.class);
+
+			// Business logic: convert the JSON string values into uppercase.
+			if (kafkaEntity.getValue() != null) {
+				Map<String, Object> valueMap = mapper.fromJson(kafkaEntity.getValue(), Map.class);
+				if (valueMap != null) {
+					valueMap.forEach((k, v) -> valueMap.put(k,
+							v != null && v instanceof String ? ((String) v).toUpperCase() : null));
+					return mapper.toString(valueMap);
+				}
+			}
+
+			return mapper.toString(null);
+		};
+	}
+}

spring-cloud-function-samples/function-sample-azure-kafka-trigger/src/main/java/example/UppercaseHandler.java

@@ -0,0 +1,69 @@
+/*
+ * Copyright 2022 the original author or authors.
+ *
+ * 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.
+ */
+
+package example;
+
+import com.microsoft.azure.functions.BrokerAuthenticationMode;
+import com.microsoft.azure.functions.BrokerProtocol;
+import com.microsoft.azure.functions.ExecutionContext;
+import com.microsoft.azure.functions.OutputBinding;
+import com.microsoft.azure.functions.annotation.FunctionName;
+import com.microsoft.azure.functions.annotation.KafkaOutput;
+import com.microsoft.azure.functions.annotation.KafkaTrigger;
+
+import org.springframework.cloud.function.adapter.azure.FunctionInvoker;
+import org.springframework.messaging.Message;
+import org.springframework.messaging.support.MessageBuilder;
+
+public class UppercaseHandler extends FunctionInvoker<Message<String>, String> {
+
+    
+    @FunctionName("KafkaTrigger")
+    public void execute(
+        @KafkaTrigger(
+            name = "KafkaTrigger", 
+            topic = "%TriggerKafkaTopic%", 
+            brokerList = "%BrokerList%", 
+            consumerGroup = "$Default", 
+            username = "%ConfluentCloudUsername%", 
+            password = "ConfluentCloudPassword", 
+            authenticationMode = BrokerAuthenticationMode.PLAIN, 
+            protocol = BrokerProtocol.PLAINTEXT,
+            // protocol = BrokerProtocol.SASLSSL,
+            // sslCaLocation = "confluent_cloud_cacert.pem", // Enable this line for windows.
+            dataType = "string") String kafkaEventData,
+        @KafkaOutput(
+            name = "kafkaOutput",
+            topic = "output",  
+            brokerList="%BrokerList%",
+            username = "%ConfluentCloudUsername%", 
+            password = "ConfluentCloudPassword",
+            authenticationMode = BrokerAuthenticationMode.PLAIN,
+            // sslCaLocation = "confluent_cloud_cacert.pem", // Enable this line for windows.  
+            protocol = BrokerProtocol.PLAINTEXT
+            //protocol = BrokerProtocol.SASLSSL
+        )  OutputBinding<String> output,
+        final ExecutionContext context) {
+
+        context.getLogger().info(kafkaEventData);
+
+        Message<String> message = MessageBuilder.withPayload(kafkaEventData).build();
+
+        String response = handleRequest(message, context);
+
+        output.setValue(response);
+    }
+}

spring-cloud-function-samples/function-sample-azure-kafka-trigger/src/main/java/example/entity/KafkaEntity.java

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+/*
+ * Copyright 2022 the original author or authors.
+ *
+ * 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.
+ */
+package example.entity;
+
+import com.fasterxml.jackson.annotation.JsonProperty;
+
+public class KafkaEntity {
+    @JsonProperty("Offset")
+    private int offset;
+    @JsonProperty("Partition")
+    private int partition;
+    @JsonProperty("Timestamp")
+    private String timestamp;
+    @JsonProperty("Topic")
+    private String topic;
+    @JsonProperty("Key")
+    private String key;
+    @JsonProperty("Value")
+    private String value;
+    @JsonProperty("Headers")
+    private KafkaHeaders[] headers;
+
+    public int getOffset() {
+        return offset;
+    }
+
+    public void setOffset(int offset) {
+        this.offset = offset;
+    }
+
+    public int getPartition() {
+        return partition;
+    }
+
+    public void setPartition(int partition) {
+        this.partition = partition;
+    }
+
+    public String getTimestamp() {
+        return timestamp;
+    }
+
+    public void setTimestamp(String timestamp) {
+        this.timestamp = timestamp;
+    }
+
+    public String getTopic() {
+        return topic;
+    }
+
+    public void setTopic(String topic) {
+        this.topic = topic;
+    }
+
+    public String getValue() {
+        return value;
+    }
+
+    
+    public void setValue(String value) {
+        this.value = value;
+    }
+
+    public KafkaHeaders[] getHeaders() {
+        return headers;
+    }
+
+    public void setHeaders(KafkaHeaders[] headers) {
+        this.headers = headers;
+    }
+
+    public String getKey() {
+        return key;
+    }
+
+    public void setKey(String key) {
+        this.key = key;
+    }
+
+}

spring-cloud-function-samples/function-sample-azure-kafka-trigger/src/main/java/example/entity/KafkaHeaders.java

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+/*
+ * Copyright 2022 the original author or authors.
+ *
+ * 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.
+ */
+package example.entity;
+
+import com.fasterxml.jackson.annotation.JsonProperty;
+
+public class KafkaHeaders {
+    @JsonProperty("Key")
+    private String key;
+    @JsonProperty("Value")
+    private String value;
+
+    public String getKey() {
+        return key;
+    }
+
+    public void setKey(String key) {
+        this.key = key;
+    }
+
+    public String getValue() {
+        return value;
+    }
+
+    public void setValue(String value) {
+        this.value = value;
+    }
+
+}