Added UCVolumeClient Interface and Class Implementation with Tests + prefixExists feature (#186)

* Saving my work so far

* One basic test case working in DriverTester

* Updated working of prefixExists testcase with LIST files instead of SHOW VOLUMES

* Added basic test functions for many methods in DriverTester

* Saving my work - tests + prefix exists unit and parameterised test

* Added Interface and Class implementation of UCVolumeClient along with tests

* did mvn spotless:apply

* Addressed Madhav and Samikshya's comments. Added a case sensitive toggle for the prefixExists function.

* forgot mvn spotless apply

* minor changes

* minor changes

* Implemented Madhav's overloading suggestion + added logger statements

* minor changes

* addressed comments

Author: agnipratimnag-db

src/main/java/com/databricks/jdbc/client/IDatabricksUCVolumeClient.java

@@ -0,0 +1,21 @@
+package com.databricks.jdbc.client;
+
+import java.sql.SQLException;
+
+public interface IDatabricksUCVolumeClient {
+
+  /**
+   * prefixExists(): Determines if a specific prefix (folder-like structure) exists in the UC Volume
+   * The prefix that we are looking for must be a part of the file name.
+   *
+   * @param catalog the catalog name of the cloud storage
+   * @param schema the schema name of the cloud storage
+   * @param volume the UC volume name of the cloud storage
+   * @param prefix the prefix to check for existence
+   * @param caseSensitive a boolean indicating whether the check should be case sensitive or not
+   * @return a boolean indicating whether the prefix exists or not
+   */
+  boolean prefixExists(
+      String catalog, String schema, String volume, String prefix, boolean caseSensitive)
+      throws SQLException;
+}

src/main/java/com/databricks/jdbc/client/impl/sdk/DatabricksUCVolumeClient.java

@@ -0,0 +1,61 @@
+package com.databricks.jdbc.client.impl.sdk;
+
+import com.databricks.jdbc.client.IDatabricksUCVolumeClient;
+import java.sql.*;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/** Implementation for DatabricksUCVolumeClient */
+public class DatabricksUCVolumeClient implements IDatabricksUCVolumeClient {
+
+  private final Connection connection;
+
+  private static final Logger LOGGER = LoggerFactory.getLogger(DatabricksSdkClient.class);
+
+  public DatabricksUCVolumeClient(Connection connection) {
+    this.connection = connection;
+  }
+
+  private String createListQuery(String catalog, String schema, String volume) {
+    return String.format("LIST '/Volumes/%s/%s/%s/'", catalog, schema, volume);
+  }
+
+  public boolean prefixExists(String catalog, String schema, String volume, String prefix)
+      throws SQLException {
+    return prefixExists(catalog, schema, volume, prefix, true);
+  }
+
+  @Override
+  public boolean prefixExists(
+      String catalog, String schema, String volume, String prefix, boolean caseSensitive)
+      throws SQLException {
+
+    LOGGER.info(
+        "Entering prefixExists method with parameters: catalog={}, schema={}, volume={}, prefix={}, caseSensitive={}",
+        catalog,
+        schema,
+        volume,
+        prefix,
+        caseSensitive);
+
+    String listFilesSQLQuery = createListQuery(catalog, schema, volume);
+
+    try (Statement statement = connection.createStatement()) {
+      ResultSet resultSet = statement.executeQuery(listFilesSQLQuery);
+      LOGGER.info("SQL query executed successfully");
+
+      boolean exists = false;
+      while (resultSet.next()) {
+        String fileName = resultSet.getString("name");
+        if (fileName.regionMatches(!caseSensitive, 0, prefix, 0, prefix.length())) {
+          exists = true;
+          break;
+        }
+      }
+      return exists;
+    } catch (SQLException e) {
+      LOGGER.error("SQL query execution failed", e);
+      throw e;
+    }
+  }
+}

src/test/java/com/databricks/jdbc/core/DatabricksUCVolumeClientTest.java

@@ -0,0 +1,53 @@
+package com.databricks.jdbc.core;
+
+import static com.databricks.jdbc.TestConstants.*;
+import static org.junit.jupiter.api.Assertions.*;
+import static org.mockito.Mockito.*;
+
+import com.databricks.jdbc.client.impl.sdk.DatabricksUCVolumeClient;
+import java.sql.*;
+import java.util.stream.Stream;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
+import org.mockito.Mock;
+import org.mockito.junit.jupiter.MockitoExtension;
+
+@ExtendWith(MockitoExtension.class)
+public class DatabricksUCVolumeClientTest {
+
+  @Mock Connection connection;
+
+  @Mock Statement statement;
+
+  @Mock ResultSet resultSet;
+
+  @ParameterizedTest
+  @MethodSource("provideParametersForPrefixExists")
+  public void testPrefixExists(String volume, String prefix, boolean expected) throws SQLException {
+    DatabricksUCVolumeClient client = new DatabricksUCVolumeClient(connection);
+
+    when(connection.createStatement()).thenReturn(statement);
+    String listFilesSQL =
+        "LIST '/Volumes/" + TEST_CATALOG + "/" + TEST_SCHEMA + "/" + volume + "/'";
+    when(statement.executeQuery(listFilesSQL)).thenReturn(resultSet);
+    when(resultSet.next()).thenReturn(true, true, true, true, true, false);
+    when(resultSet.getString("name"))
+        .thenReturn("aBc_file1", "abC_file2", "def_file1", "efg_file2", "#!#_file3");
+
+    boolean exists = client.prefixExists(TEST_CATALOG, TEST_SCHEMA, volume, prefix, true);
+
+    assertEquals(expected, exists);
+    verify(statement).executeQuery(listFilesSQL);
+  }
+
+  private static Stream<Arguments> provideParametersForPrefixExists() {
+    return Stream.of(
+        Arguments.of("abc_volume1", "abc", false),
+        Arguments.of("abc_volume2", "xyz", false),
+        Arguments.of("abc_volume2", "def", true),
+        Arguments.of("abc_volume2", "#!", true),
+        Arguments.of("abc_volume2", "aBc", true));
+  }
+}