add a UT and docs

hudi-common/src/test/java/org/apache/hudi/common/util/TestStringUtils.java

@@ -23,6 +23,7 @@
 import java.nio.ByteBuffer;
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.Collections;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertNotEquals;
@@ -45,6 +46,14 @@ public void testStringJoin() {
     assertNotEquals(null, StringUtils.join(STRINGS));
   }
 
+  @Test
+  public void testStringJoinWithJavaImpl() {
+    assertNull(StringUtils.join(",", null));
+    assertEquals("", String.join(",", Collections.singletonList("")));
+    assertEquals(",", String.join(",", Arrays.asList("", "")));
+    assertEquals("a,", String.join(",", Arrays.asList("a", "")));
+  }
+
   @Test
   public void testStringNullToEmpty() {
     String str = "This is a test";

hudi-gcp/src/main/java/org/apache/hudi/gcp/bigquery/BigQuerySyncConfig.java

@@ -38,52 +38,53 @@ public class BigQuerySyncConfig extends HoodieSyncConfig implements Serializable
   public static final ConfigProperty<String> BIGQUERY_SYNC_PROJECT_ID = ConfigProperty
       .key("hoodie.gcp.bigquery.sync.project_id")
       .noDefaultValue()
-      .withDocumentation("");
+      .withDocumentation("Name of the target project in BigQuery");
 
   public static final ConfigProperty<String> BIGQUERY_SYNC_DATASET_NAME = ConfigProperty
       .key("hoodie.gcp.bigquery.sync.dataset_name")
       .noDefaultValue()
-      .withDocumentation("");
+      .withDocumentation("Name of the target dataset in BigQuery");
 
   public static final ConfigProperty<String> BIGQUERY_SYNC_DATASET_LOCATION = ConfigProperty
       .key("hoodie.gcp.bigquery.sync.dataset_location")
       .noDefaultValue()
-      .withDocumentation("");
+      .withDocumentation("Location of the target dataset in BigQuery");
 
   public static final ConfigProperty<String> BIGQUERY_SYNC_TABLE_NAME = ConfigProperty
       .key("hoodie.gcp.bigquery.sync.table_name")
       .noDefaultValue()
-      .withDocumentation("");
+      .withDocumentation("Name of the target table in BigQuery");
 
   public static final ConfigProperty<String> BIGQUERY_SYNC_SOURCE_URI = ConfigProperty
       .key("hoodie.gcp.bigquery.sync.source_uri")
       .noDefaultValue()
-      .withDocumentation("");
+      .withDocumentation("Name of the source uri gcs path of the table");
 
   public static final ConfigProperty<String> BIGQUERY_SYNC_SOURCE_URI_PREFIX = ConfigProperty
       .key("hoodie.gcp.bigquery.sync.source_uri_prefix")
       .noDefaultValue()
-      .withDocumentation("");
+      .withDocumentation("Name of the source uri gcs path prefix of the table");
 
   public static final ConfigProperty<String> BIGQUERY_SYNC_SYNC_BASE_PATH = ConfigProperty
       .key("hoodie.gcp.bigquery.sync.base_path")
       .noDefaultValue()
-      .withDocumentation("");
+      .withDocumentation("Base path of the hoodie table to sync");
 
   public static final ConfigProperty<String> BIGQUERY_SYNC_PARTITION_FIELDS = ConfigProperty
       .key("hoodie.gcp.bigquery.sync.partition_fields")
       .noDefaultValue()
-      .withDocumentation("");
+      .withDocumentation("Comma-delimited partition fields. Default to non-partitioned.");
 
   public static final ConfigProperty<Boolean> BIGQUERY_SYNC_USE_FILE_LISTING_FROM_METADATA = ConfigProperty
       .key("hoodie.gcp.bigquery.sync.use_file_listing_from_metadata")
       .defaultValue(false)
-      .withDocumentation("");
+      .withDocumentation("Fetch file listing from Hudi's metadata");
 
   public static final ConfigProperty<Boolean> BIGQUERY_SYNC_ASSUME_DATE_PARTITIONING = ConfigProperty
       .key("hoodie.gcp.bigquery.sync.assume_date_partitioning")
       .defaultValue(false)
-      .withDocumentation("");
+      .withDocumentation("Assume standard yyyy/mm/dd partitioning, this"
+          + " exists to support backward compatibility. If you use hoodie 0.3.x, do not set this parameter");
 
   public BigQuerySyncConfig(Properties props) {
     super(props);
@@ -94,17 +95,17 @@ public static class BigQuerySyncConfigParams {
     @ParametersDelegate()
     public final HoodieSyncConfigParams hoodieSyncConfigParams = new HoodieSyncConfigParams();
 
-    @Parameter(names = {"--project-id"}, description = "name of the target project in BigQuery", required = true)
+    @Parameter(names = {"--project-id"}, description = "Name of the target project in BigQuery", required = true)
     public String projectId;
-    @Parameter(names = {"--dataset-name"}, description = "name of the target dataset in BigQuery", required = true)
+    @Parameter(names = {"--dataset-name"}, description = "Name of the target dataset in BigQuery", required = true)
     public String datasetName;
-    @Parameter(names = {"--dataset-location"}, description = "location of the target dataset in BigQuery", required = true)
+    @Parameter(names = {"--dataset-location"}, description = "Location of the target dataset in BigQuery", required = true)
     public String datasetLocation;
-    @Parameter(names = {"--table-name"}, description = "name of the target table in BigQuery", required = true)
+    @Parameter(names = {"--table-name"}, description = "Name of the target table in BigQuery", required = true)
     public String tableName;
-    @Parameter(names = {"--source-uri"}, description = "name of the source uri gcs path of the table", required = true)
+    @Parameter(names = {"--source-uri"}, description = "Name of the source uri gcs path of the table", required = true)
     public String sourceUri;
-    @Parameter(names = {"--source-uri-prefix"}, description = "name of the source uri gcs path prefix of the table", required = true)
+    @Parameter(names = {"--source-uri-prefix"}, description = "Name of the source uri gcs path prefix of the table", required = true)
     public String sourceUriPrefix;
     @Parameter(names = {"--base-path"}, description = "Base path of the hoodie table to sync", required = true)
     public String basePath;

hudi-sync/hudi-sync-common/src/main/java/org/apache/hudi/sync/common/HoodieMetaSyncOperations.java

@@ -54,22 +54,37 @@ default void createTable(String tableName,
 
   }
 
+  /**
+   * Check if table exists in metastore.
+   */
   default boolean tableExists(String tableName) {
     return false;
   }
 
+  /**
+   * Drop table from metastore.
+   */
   default void dropTable(String tableName) {
 
   }
 
+  /**
+   * Add partitions to the table in metastore.
+   */
   default void addPartitionsToTable(String tableName, List<String> partitionsToAdd) {
 
   }
 
+  /**
+   * Update partitions to the table in metastore.
+   */
   default void updatePartitionsToTable(String tableName, List<String> changedPartitions) {
 
   }
 
+  /**
+   * Drop partitions from the table in metastore.
+   */
   default void dropPartitions(String tableName, List<String> partitionsToDrop) {
 
   }
@@ -95,10 +110,16 @@ default void createDatabase(String databaseName) {
 
   }
 
+  /**
+   * Get the schema from metastore.
+   */
   default Map<String, String> getMetastoreSchema(String tableName) {
     return Collections.emptyMap();
   }
 
+  /**
+   * Get the schema from the Hudi table on storage.
+   */
   default MessageType getStorageSchema() {
     return null;
   }
@@ -110,38 +131,65 @@ default void updateTableSchema(String tableName, MessageType newSchema) {
 
   }
 
+  /**
+   * Get the list of field schemas from metastore.
+   */
   default List<FieldSchema> getMetastoreFieldSchemas(String tableName) {
     return Collections.emptyList();
   }
 
+  /**
+   * Get the list of field schema from the Hudi table on storage.
+   */
   default List<FieldSchema> getStorageFieldSchemas() {
     return Collections.emptyList();
   }
 
+  /**
+   * Update the field comments for table in metastore, by using the ones from storage.
+   */
   default void updateTableComments(String tableName, List<FieldSchema> fromMetastore, List<FieldSchema> fromStorage) {
 
   }
 
+  /**
+   * Get the timestamp of last sync.
+   */
   default Option<String> getLastCommitTimeSynced(String tableName) {
     return Option.empty();
   }
 
+  /**
+   * Update the timestamp of last sync.
+   */
   default void updateLastCommitTimeSynced(String tableName) {
 
   }
 
+  /**
+   * Update the table properties in metastore.
+   */
   default void updateTableProperties(String tableName, Map<String, String> tableProperties) {
 
   }
 
+  /**
+   * Get the timestamp of last replication.
+   */
   default Option<String> getLastReplicatedTime(String tableName) {
     return Option.empty();
   }
 
+  /**
+   * Update the timestamp of last replication.
+   */
   default void updateLastReplicatedTimeStamp(String tableName, String timeStamp) {
 
   }
 
+  /**
+   * Delete the timestamp of last replication.
+   */
   default void deleteLastReplicatedTimeStamp(String tableName) {
 
   }