Add javadoc code comments (#206)

* Separate stream and batch event conversion part3

* Separate stream and batch event conversion part3

* Separate stream and batch event conversion part3

debezium-server-bigquery-sinks/src/main/java/io/debezium/server/bigquery/BaseBigqueryStorageConfig.java

@@ -9,7 +9,11 @@
 import java.util.Optional;
 import java.util.Properties;
 
-
+/**
+ * Abstract base class for BigQuery storage configuration.
+ * <p>
+ * Provides common methods for accessing Debezium configuration properties
+ */
 public abstract class BaseBigqueryStorageConfig {
   protected static final Logger LOG = LoggerFactory.getLogger(BaseBigqueryStorageConfig.class);
   protected Properties configCombined = new Properties();

debezium-server-bigquery-sinks/src/main/java/io/debezium/server/bigquery/BaseChangeConsumer.java

@@ -38,7 +38,12 @@
 import java.util.stream.Collectors;
 
 /**
- * Implementation of the consumer that delivers the messages into Amazon S3 destination.
+ * Abstract base class for Debezium change consumers that deliver messages to a BigQuery destination.
+ * <p>This class provides a foundation for building Debezium change consumers that handle
+ * incoming change events and deliver them to a BigQuery destination. It implements the
+ * `DebeziumEngine.ChangeConsumer` interface, defining the `handleBatch` method for processing
+ * batches of change events. Concrete implementations of this class need to provide specific logic
+ * for uploading or persisting the converted data to the BigQuery destination.
  *
  * @author Ismail Simsek
  */

debezium-server-bigquery-sinks/src/main/java/io/debezium/server/bigquery/BaseRecordConverter.java

@@ -19,6 +19,12 @@
 import java.util.stream.Collectors;
 
 /**
+ * Abstract base class for Debezium event record conversion to BigQuery format.
+ * <p>This class provides the foundation for converting Debezium event records into a format
+ * suitable for writing to BigQuery tables. It handles common tasks like schema conversion,
+ * table constraint generation, and clustering configuration. Concrete implementations of this
+ * class can extend this functionality for specific use cases.
+ *
  * @author Ismail Simsek
  */
 public abstract class BaseRecordConverter implements RecordConverter {

debezium-server-bigquery-sinks/src/main/java/io/debezium/server/bigquery/BatchBigqueryChangeConsumer.java

@@ -29,10 +29,14 @@
 import java.util.Optional;
 
 /**
- * Implementation of the consumer that delivers the messages into Amazon S3 destination.
+ * Implementation of a Debezium change consumer that delivers batches of events to BigQuery tables.
+ * <p>This class extends the `BaseChangeConsumer` and provides functionality for uploading batches of
+ * Debezium change events to BigQuery tables. It leverages the BigQuery Java client library
+ * to perform data loading and table management tasks.
  *
  * @author Ismail Simsek
  */
+
 @Named("bigquerybatch")
 @Dependent
 public class BatchBigqueryChangeConsumer<T> extends BaseChangeConsumer {

debezium-server-bigquery-sinks/src/main/java/io/debezium/server/bigquery/ConsumerUtil.java

@@ -38,6 +38,8 @@
 import java.util.Optional;
 
 /**
+ * Utility class for common BigQuery operations in Debezium Server.
+ *
  * @author Ismail Simsek
  */
 public class ConsumerUtil {

debezium-server-bigquery-sinks/src/main/java/io/debezium/server/bigquery/RecordConverter.java

@@ -5,6 +5,7 @@
 import com.google.cloud.bigquery.Schema;
 import com.google.cloud.bigquery.TableConstraints;
 import io.debezium.DebeziumException;
+import org.json.JSONObject;
 
 public interface RecordConverter {
   String destination();
@@ -15,6 +16,24 @@ default <T> T convert(Schema schema) throws DebeziumException {
     return convert(schema, false, false);
   }
 
+  /**
+   * Converts a Debezium event for BigQuery ingestion.
+   *
+   * <p>This method transforms a Debezium event into a format suitable for writing to BigQuery.
+   * It performs value conversions based on the specified BigQuery schema to ensure compatibility
+   * with the target data types.
+   *
+   * @param schema            The BigQuery schema to use for data type conversions.
+   * @param upsert            Indicates whether to enable upsert operations. When set to `true`, a
+   *                          `_CHANGE_TYPE` column is added to track record changes (insert, update, delete).
+   * @param upsertKeepDeletes When set to `true` in conjunction with `upsert`, the last deleted
+   *                          row is retained.
+   * @param <T>               The return type of the converted event. This can be a serialized JSON string
+   *                          for batch operations or a {@link JSONObject} for stream operations, depending on the
+   *                          specific implementation.
+   * @return The converted Debezium event, ready for BigQuery ingestion.
+   * @throws DebeziumException If an error occurs during the conversion process.
+   */
   <T> T convert(Schema schema, boolean upsert, boolean upsertKeepDeletes) throws DebeziumException;
 
   JsonNode key();
@@ -23,9 +42,45 @@ default <T> T convert(Schema schema) throws DebeziumException {
 
   JsonNode keySchema();
 
+
+  /**
+   * Extracts table constraints from the Debezium event's key schema.
+   *
+   * <p>This method analyzes the provided Debezium event's key schema and generates a
+   * corresponding BigQuery table constraints configuration. The primary key constraint
+   * is derived from the fields present in the key schema. This configuration can be
+   * used to optimize table storage and query performance in BigQuery.
+   *
+   * @return The generated BigQuery table {@link TableConstraints}.
+   */
   TableConstraints tableConstraints();
 
+
+  /**
+   * Determines the clustering fields for the BigQuery table.
+   *
+   * <p>This method extracts field names from the Debezium event's key schema and combines them
+   * with a user-provided clustering field (defaulting to `__source_ts_ms`) to create a suitable
+   * clustering configuration for the BigQuery table. Clustering the table on these fields
+   * can significantly improve query performance, especially for time-series and analytical workloads.
+   *
+   * @param clusteringField The additional field to use for clustering, beyond the fields
+   *                        extracted from the key schema.
+   * @return The generated BigQuery {@link Clustering} configuration.
+   */
   Clustering tableClustering(String clusteringField);
 
+
+  /**
+   * Transforms a Debezium event's value schema into a corresponding BigQuery schema.
+   *
+   * <p>This method analyzes the provided Debezium event's value schema and generates a
+   * compatible BigQuery schema. It considers factors like field types and
+   * the `binaryAsString` flag to accurately map the schema.
+   *
+   * @param binaryAsString Indicates whether binary fields should be represented as strings
+   *                       or binary types in the resulting BigQuery schema.
+   * @return The generated BigQuery {@link Schema}.
+   */
   Schema tableSchema(Boolean binaryAsString);
 }

debezium-server-bigquery-sinks/src/main/java/io/debezium/server/bigquery/StreamBigqueryChangeConsumer.java

@@ -36,10 +36,14 @@
 import java.util.stream.Collectors;
 
 /**
- * Implementation of the consumer that delivers the messages to Bigquery
+ * Implementation of a Debezium change consumer that delivers events to BigQuery tables in a streaming manner.
+ * <p>This class extends the `BaseChangeConsumer` and provides functionality for streaming batches of
+ * Debezium change events to BigQuery tables using the BigQuery Write API. It offers features like
+ * upsert, deduplication, and table schema management.
  *
  * @author Ismail Simsek
  */
+
 @Named("bigquerystream")
 @Dependent
 @Beta

debezium-server-bigquery-sinks/src/main/java/io/debezium/server/bigquery/StreamDataWriter.java

@@ -14,7 +14,11 @@
 import java.util.concurrent.Executors;
 import java.util.concurrent.atomic.AtomicInteger;
 
-
+/**
+ * Class responsible for writing data to BigQuery in a streaming manner using the BigQuery Write API.
+ * This class creates and manages a {@link JsonStreamWriter} writer for a specific BigQuery table. It offers functionality
+ * for adding data in JSON format and handling potential errors during the write process.
+ */
 public class StreamDataWriter {
   private static final int MAX_RECREATE_COUNT = 3;
   private final BigQueryWriteClient client;