#333 Make VirtualSchemaAdapter & AdapterFactory AutoCloseable for resource cleanup

doc/changes/changes_18.0.2.md

@@ -1,10 +1,14 @@
-# Common Module of Exasol Virtual Schemas Adapters 18.0.2, released 2026-??-??
+# Common Module of Exasol Virtual Schemas Adapters 18.0.2, released 2026-06-02
 
 Code name: Improve code quality
 
 ## Summary
 
-## Breaking Changes
+This release includes many small bugfixes and code improvements. Some methods are now deprecated and will be removed in a future release.
+
+The release also makes interfaces `VirtualSchemaAdapter` and `AdapterFactory` `AutoCloseable`. This allows adapters to cleanup resources after processing a request. The interfaces provide a `default` implementation of `close()`, so that users of the interface don't need to change.
+
+## Deprecations
 
 * `Capabilities.subtractCapabilities()` is now deprecated for removal and delegates to the new pure `Capabilities.subtract()` implementation. Code that relied on the previous side effect of mutating the receiver must be adapted (#305).
 * Constructor `ColumnMetadata.Builder()` is now deprecated for removal. Use `ColumnMetadata.builder()` to create a new instance (#306).
@@ -14,6 +18,10 @@ Code name: Improve code quality
 * Constructor `VersionCollector()` is now deprecated for removal. Use `VersionCollector(final String path)` to create a new instance (#312)
 * Methods `SqlFunctionAggregateListagg.Behavior.setTruncationType(TruncationType)` and `SqlFunctionAggregateListagg.Behavior.setTruncationFiller(SqlLiteralString)` are deprecated for removal.
 
+## Features
+
+* #333: Make `VirtualSchemaAdapter` and `AdapterFactory` `AutoCloseable`
+
 ## Bugfixes
 
 * #305: Fixed `Capabilities.subtractCapabilities()` so it no longer mutates the receiver. Added the pure `Capabilities.subtract()` method.

src/main/java/com/exasol/adapter/AdapterFactory.java

@@ -3,7 +3,7 @@
 /**
  * Factory that creates a {@link VirtualSchemaAdapter}
  */
-public interface AdapterFactory {
+public interface AdapterFactory extends AutoCloseable {
     /**
      * Create a new {@link VirtualSchemaAdapter}
      *
@@ -48,4 +48,9 @@ public interface AdapterFactory {
      * @return short tag for the adapter project
      */
     public String getAdapterProjectShortTag();
+
+    @Override
+    public default void close() {
+        // By default, there are no resources to be closed. Adapters can override this method if needed.
+    }
 }

src/main/java/com/exasol/adapter/RequestDispatcher.java

@@ -58,14 +58,15 @@ private static String processAdapterCall(final ExaMetadata metadata, final Strin
         }
         logVersionInformation();
         logRawRequest(rawRequest);
-        final AdapterFactory adapterFactory = getAdapterFactory();
-        try (TelemetryClient telemetryClient = createTelemetryClient(adapterFactory, adapterRequest)) {
+        try (final AdapterFactory adapterFactory = getAdapterFactory();
+                TelemetryClient telemetryClient = createTelemetryClient(adapterFactory, adapterRequest)) {
             final AdapterContext context = new AdapterContext(telemetryClient);
-            final VirtualSchemaAdapter virtualSchemaAdapter = adapterFactory.createAdapter(context);
-            final AdapterCallExecutor adapterCallExecutor = new AdapterCallExecutor(virtualSchemaAdapter, telemetryClient);
-            final String response = adapterCallExecutor.executeAdapterCall(adapterRequest, metadata);
-            logRawResponse(response);
-            return response;
+            try (final VirtualSchemaAdapter virtualSchemaAdapter = adapterFactory.createAdapter(context)) {
+                final AdapterCallExecutor adapterCallExecutor = new AdapterCallExecutor(virtualSchemaAdapter, telemetryClient);
+                final String response = adapterCallExecutor.executeAdapterCall(adapterRequest, metadata);
+                logRawResponse(response);
+                return response;
+            }
         }
     }
 

src/main/java/com/exasol/adapter/VirtualSchemaAdapter.java

@@ -6,12 +6,11 @@
 
 /**
  * Interface for Virtual Schema Adapters.
- *
  * <p>
  * This interface provides a number of handler functions for different types of requests a virtual schema adapter can
  * receive from the Exasol core database.
  */
-public interface VirtualSchemaAdapter {
+public interface VirtualSchemaAdapter extends AutoCloseable {
     /**
      * Create a Virtual Schema
      *
@@ -75,4 +74,9 @@ public GetCapabilitiesResponse getCapabilities(final ExaMetadata metadata, final
      * @throws AdapterException if the adapter can't handle the request
      */
     public PushDownResponse pushdown(final ExaMetadata metadata, final PushDownRequest request) throws AdapterException;
-}
+
+    @Override
+    public default void close() {
+        // By default, there are no resources to be closed. Adapters can override this method if needed.
+    }
+}

src/test/java/com/exasol/adapter/AdapterFactoryTest.java

@@ -0,0 +1,36 @@
+package com.exasol.adapter;
+
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+
+import org.junit.jupiter.api.Test;
+
+class AdapterFactoryTest {
+
+    @Test
+    void testDefaultCloseDoesNotThrow() {
+        final AdapterFactory factory = new AdapterFactoryImplementation();
+        assertDoesNotThrow(factory::close);
+    }
+
+    private final class AdapterFactoryImplementation implements AdapterFactory {
+        @Override
+        public VirtualSchemaAdapter createAdapter(final AdapterContext context) {
+            return null;
+        }
+
+        @Override
+        public String getAdapterVersion() {
+            return "test";
+        }
+
+        @Override
+        public String getAdapterName() {
+            return "test";
+        }
+
+        @Override
+        public String getAdapterProjectShortTag() {
+            return "TEST";
+        }
+    }
+}

src/test/java/com/exasol/adapter/RequestDispatcherTest.java

@@ -37,6 +37,8 @@ class RequestDispatcherTest {
     @BeforeEach
     void beforeEach() {
         resetRootLogger();
+        StubAdapterFactory.resetClosed();
+        StubAdapter.resetClosed();
     }
 
     /**
@@ -121,6 +123,24 @@ void testDispatchPushDownRequest() throws AdapterException {
         adapterCall(rawRequest).withResponse("{\"type\":\"pushdown\",\"sql\":\"SELECT * FROM FOOBAR\"}").verify();
     }
 
+    @Test
+    void testFactoryIsClosedAfterDispatch() throws AdapterException {
+        adapterCall("{ \"type\" : \"createVirtualSchema\", " + DEFAULT_REQUEST_PARTS + "}")
+                .withResponse(
+                        "{\"type\":\"createVirtualSchema\",\"schemaMetadata\":{\"tables\":[],\"adapterNotes\":\"\"}}")
+                .verify();
+        assertThat(StubAdapterFactory.wasClosed(), equalTo(true));
+    }
+
+    @Test
+    void testAdapterIsClosedAfterDispatch() throws AdapterException {
+        adapterCall("{ \"type\" : \"createVirtualSchema\", " + DEFAULT_REQUEST_PARTS + "}")
+                .withResponse(
+                        "{\"type\":\"createVirtualSchema\",\"schemaMetadata\":{\"tables\":[],\"adapterNotes\":\"\"}}")
+                .verify();
+        assertThat(StubAdapter.wasClosed(), equalTo(true));
+    }
+
     private AdapterCallVerifier adapterCall(final String rawRequest) {
         return new AdapterCallVerifier(rawRequest);
     }

src/test/java/com/exasol/adapter/StubAdapter.java

@@ -11,6 +11,8 @@
  * This class implements a stub for a VirtualSchemaAdapter
  */
 public class StubAdapter implements VirtualSchemaAdapter {
+    private static boolean closed = false;
+
     public StubAdapter(final AdapterContext context) {
     }
 
@@ -45,4 +47,17 @@ public GetCapabilitiesResponse getCapabilities(final ExaMetadata metadata, final
     public PushDownResponse pushdown(final ExaMetadata metadata, final PushDownRequest request) {
         return PushDownResponse.builder().pushDownSql("SELECT * FROM FOOBAR").build();
     }
+
+    @Override
+    public void close() {
+        closed = true;
+    }
+
+    static void resetClosed() {
+        closed = false;
+    }
+
+    static boolean wasClosed() {
+        return closed;
+    }
 }

src/test/java/com/exasol/adapter/StubAdapterFactory.java

@@ -4,6 +4,8 @@
 import static org.hamcrest.Matchers.notNullValue;
 
 public class StubAdapterFactory implements AdapterFactory {
+    private static boolean closed = false;
+
     @Override
     public VirtualSchemaAdapter createAdapter(final AdapterContext context) {
         assertThat(context.getTelemetryClient(), notNullValue());
@@ -24,4 +26,17 @@ public String getAdapterName() {
     public String getAdapterProjectShortTag() {
         return "VSSTUB";
     }
+
+    @Override
+    public void close() {
+        closed = true;
+    }
+
+    static void resetClosed() {
+        closed = false;
+    }
+
+    static boolean wasClosed() {
+        return closed;
+    }
 }

src/test/java/com/exasol/adapter/VirtualSchemaAdapterTest.java

@@ -0,0 +1,50 @@
+package com.exasol.adapter;
+
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+
+import org.junit.jupiter.api.Test;
+
+import com.exasol.ExaMetadata;
+import com.exasol.adapter.request.*;
+import com.exasol.adapter.response.*;
+
+class VirtualSchemaAdapterTest {
+
+    @Test
+    void testDefaultCloseDoesNotThrow() {
+        final VirtualSchemaAdapter adapter = new VirtualSchemaAdapterImplementation();
+        assertDoesNotThrow(adapter::close);
+    }
+
+    private final class VirtualSchemaAdapterImplementation implements VirtualSchemaAdapter {
+        @Override
+        public CreateVirtualSchemaResponse createVirtualSchema(final ExaMetadata metadata, final CreateVirtualSchemaRequest request) {
+            return null;
+        }
+
+        @Override
+        public DropVirtualSchemaResponse dropVirtualSchema(final ExaMetadata metadata, final DropVirtualSchemaRequest request) {
+            return null;
+        }
+
+        @Override
+        public RefreshResponse refresh(final ExaMetadata metadata, final RefreshRequest request) {
+            return null;
+        }
+
+        @Override
+        public SetPropertiesResponse setProperties(final ExaMetadata metadata, final SetPropertiesRequest request) {
+            return null;
+        }
+
+        @Override
+        public GetCapabilitiesResponse getCapabilities(final ExaMetadata metadata, final GetCapabilitiesRequest request) {
+            return null;
+        }
+
+        @Override
+        public PushDownResponse pushdown(final ExaMetadata metadata, final PushDownRequest request) {
+            return null;
+        }
+    }
+}