doesResourceExist function (#1608)

* Add existence check to resourcefactory

* With and without session tests

fcrepo-kernel-api/src/main/java/org/fcrepo/kernel/api/models/ResourceFactory.java

@@ -17,6 +17,8 @@
  */
 package org.fcrepo.kernel.api.models;
 
+import java.time.Instant;
+
 import org.fcrepo.kernel.api.Transaction;
 import org.fcrepo.kernel.api.exception.PathNotFoundException;
 
@@ -73,4 +75,13 @@ public <T extends FedoraResource> T getResource(final String identifier,
      */
     public <T extends FedoraResource> T getResource(final Transaction transaction, final String identifier,
             final Class<T> clazz) throws PathNotFoundException;
+
+    /**
+     * Check if a resource exists.
+     * @param transaction The current transaction or null if read-only.
+     * @param fedoraId The internal identifier
+     * @param version The version datetime or null for head.
+     * @return True if the identifier resolves to a resource.
+     */
+    public boolean doesResourceExist(final Transaction transaction, final String fedoraId, final Instant version);
 }

fcrepo-kernel-impl/src/main/java/org/fcrepo/kernel/impl/models/ResourceFactoryImpl.java

@@ -21,9 +21,12 @@
 import static org.fcrepo.kernel.api.RdfLexicon.DIRECT_CONTAINER;
 import static org.fcrepo.kernel.api.RdfLexicon.INDIRECT_CONTAINER;
 import static org.fcrepo.kernel.api.RdfLexicon.NON_RDF_SOURCE;
+import static org.slf4j.LoggerFactory.getLogger;
 
 import javax.inject.Inject;
 
+import java.time.Instant;
+
 import org.fcrepo.kernel.api.Transaction;
 import org.fcrepo.kernel.api.exception.PathNotFoundException;
 import org.fcrepo.kernel.api.exception.RepositoryRuntimeException;
@@ -36,6 +39,7 @@
 import org.fcrepo.persistence.api.PersistentStorageSessionManager;
 import org.fcrepo.persistence.api.exceptions.PersistentItemNotFoundException;
 import org.fcrepo.persistence.api.exceptions.PersistentStorageException;
+import org.slf4j.Logger;
 import org.springframework.stereotype.Component;
 
 
@@ -48,6 +52,8 @@
 @Component
 public class ResourceFactoryImpl implements ResourceFactory {
 
+    private static final Logger LOGGER = getLogger(ResourceFactoryImpl.class);
+
     @Inject
     private PersistentStorageSessionManager persistentStorageSessionManager;
 
@@ -75,6 +81,37 @@ public <T extends FedoraResource> T getResource(final Transaction transaction, f
         return clazz.cast(getResource(transaction, identifier));
     }
 
+    @Override
+    public boolean doesResourceExist(final Transaction transaction, final String fedoraId, final Instant version) {
+        // TODO: Check the index first.
+
+        final PersistentStorageSession psSession;
+        if (transaction == null) {
+            psSession = persistentStorageSessionManager.getReadOnlySession();
+        } else {
+            psSession = persistentStorageSessionManager.getSession(transaction.getId());
+        }
+        try {
+            psSession.getHeaders(fedoraId, version);
+            return true;
+        } catch (PersistentItemNotFoundException e) {
+            // Object doesn't exist.
+            return false;
+        } catch (PersistentStorageException e) {
+            // Other error, pass along.
+            throw new RepositoryRuntimeException(e);
+        } finally {
+            if (transaction == null) {
+                // Commit session (if read-only) so it doesn't hang around.
+                try {
+                    psSession.commit();
+                } catch (PersistentStorageException e) {
+                    LOGGER.error("Error committing session, message: {}", e.getMessage());
+                }
+            }
+        }
+    }
+
     /**
      * Returns the appropriate FedoraResource class for an object based on the provided headers
      *

fcrepo-kernel-impl/src/test/java/org/fcrepo/kernel/impl/models/ResourceFactoryImplTest.java

@@ -22,6 +22,7 @@
 import static org.fcrepo.kernel.api.RdfLexicon.INDIRECT_CONTAINER;
 import static org.fcrepo.kernel.api.RdfLexicon.NON_RDF_SOURCE;
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertTrue;
 import static org.mockito.ArgumentMatchers.eq;
 import static org.mockito.ArgumentMatchers.nullable;
@@ -43,6 +44,7 @@
 import org.fcrepo.persistence.api.PersistentStorageSession;
 import org.fcrepo.persistence.api.PersistentStorageSessionManager;
 import org.fcrepo.persistence.api.exceptions.PersistentItemNotFoundException;
+import org.fcrepo.persistence.api.exceptions.PersistentSessionClosedException;
 import org.fcrepo.persistence.api.exceptions.PersistentStorageException;
 import org.fcrepo.persistence.common.ResourceHeadersImpl;
 import org.junit.Before;
@@ -245,6 +247,44 @@ public void getResource_Binary_StorageException() throws Exception {
         factory.getResource(fedoraId);
     }
 
+    @Test
+    public void doesResourceExists_Exists_WithSession() throws Exception {
+        final boolean answer = factory.doesResourceExist(mockTx, fedoraId, null);
+        assertTrue(answer);
+    }
+
+    @Test
+    public void doesResourceExists_Exists_WithoutSession() throws Exception {
+        final boolean answer = factory.doesResourceExist(null, fedoraId, null);
+        assertTrue(answer);
+    }
+
+    @Test
+    public void doesResourceExist_DoesntExist_WithSession() throws Exception {
+        when(psSession.getHeaders(fedoraId, null)).thenThrow(PersistentItemNotFoundException.class);
+        final boolean answer = factory.doesResourceExist(mockTx, fedoraId, null);
+        assertFalse(answer);
+    }
+
+    @Test
+    public void doesResourceExist_DoesntExist_WithoutSession() throws Exception {
+        when(psSession.getHeaders(fedoraId, null)).thenThrow(PersistentItemNotFoundException.class);
+        final boolean answer = factory.doesResourceExist(null, fedoraId, null);
+        assertFalse(answer);
+    }
+
+    @Test(expected = RepositoryRuntimeException.class)
+    public void doesResourceExist_Exception_WithSession() throws Exception {
+        when(psSession.getHeaders(fedoraId, null)).thenThrow(PersistentSessionClosedException.class);
+        factory.doesResourceExist(mockTx, fedoraId, null);
+    }
+
+    @Test(expected = RepositoryRuntimeException.class)
+    public void doesResourceExist_Exception_WithoutSession() throws Exception {
+        when(psSession.getHeaders(fedoraId, null)).thenThrow(PersistentSessionClosedException.class);
+        factory.doesResourceExist(null, fedoraId, null);
+    }
+
     private void assertStateFieldsMatches(final FedoraResource resc) {
         assertEquals(CREATED_DATE, resc.getCreatedDate());
         assertEquals(CREATED_BY, resc.getCreatedBy());