[cache] Added 'ByteArrayFileCache' (#1723)

Signed-off-by: Christoph Weitkamp <github@christophweitkamp.de>

bundles/org.openhab.core/.classpath

@@ -28,5 +28,10 @@
 			<attribute name="test" value="true"/>
 		</attributes>
 	</classpathentry>
+	<classpathentry excluding="**" kind="src" output="target/test-classes" path="src/test/resources">
+		<attributes>
+			<attribute name="maven.pomderived" value="true"/>
+		</attributes>
+	</classpathentry>
 	<classpathentry kind="output" path="target/classes"/>
 </classpath>

bundles/org.openhab.core/src/main/java/org/openhab/core/OpenHAB.java

@@ -106,9 +106,7 @@ public class OpenHAB {
 
     /**
      * Returns the user data folder path name. The main user data folder <code>&lt;openhab-home&gt;/userdata</code> can
-     * be
+     * be overwritten by setting the System property <code>openhab.userdata</code>.
-     * overwritten by setting
-     * the System property <code>openhab.userdata</code>.
      *
      * @return the user data folder path name
      */

bundles/org.openhab.core/src/main/java/org/openhab/core/cache/ByteArrayFileCache.java

@@ -0,0 +1,290 @@
+/**
+ * Copyright (c) 2010-2020 Contributors to the openHAB project
+ *
+ * See the NOTICE file(s) distributed with this work for additional
+ * information.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License 2.0 which is available at
+ * http://www.eclipse.org/legal/epl-2.0
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ */
+package org.openhab.core.cache;
+
+import java.io.File;
+import java.io.FileNotFoundException;
+import java.io.IOException;
+import java.math.BigInteger;
+import java.nio.file.Files;
+import java.time.Duration;
+import java.util.Arrays;
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+
+import org.eclipse.jdt.annotation.NonNullByDefault;
+import org.eclipse.jdt.annotation.Nullable;
+import org.openhab.core.OpenHAB;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * This is a simple file based cache implementation. It is not thread-safe.
+ *
+ * @author Christoph Weitkamp - Initial contribution
+ */
+@NonNullByDefault
+public class ByteArrayFileCache {
+
+    private final Logger logger = LoggerFactory.getLogger(ByteArrayFileCache.class);
+
+    static final String CACHE_FOLDER_NAME = "cache";
+    private static final char EXTENSION_SEPARATOR = '.';
+
+    private final File cacheFolder;
+
+    private final Duration expiry;
+    private final Map<String, File> filesInCache = new ConcurrentHashMap<>();
+
+    /**
+     * Creates a new {@link ByteArrayFileCache} instance for a service. Creates a <code>cache</code> folder under
+     * <code>$OPENHAB_USERDATA/cache/$servicePID</code>.
+     *
+     * @param servicePID PID of the service
+     */
+    public ByteArrayFileCache(String servicePID) {
+        this(servicePID, Duration.ZERO);
+    }
+
+    /**
+     * Creates a new {@link ByteArrayFileCache} instance for a service. Creates a <code>cache</code> folder under
+     * <code>$OPENHAB_USERDATA/cache/$servicePID/</code>.
+     *
+     * @param servicePID PID of the service
+     * @param expiry the duration for how long the files stay valid in the cache. Must be positive. 0 to
+     *            disable this functionality.
+     */
+    public ByteArrayFileCache(String servicePID, Duration expiry) {
+        // TODO track and limit folder size
+        // TODO support user specific folder
+        cacheFolder = new File(new File(OpenHAB.getUserDataFolder(), CACHE_FOLDER_NAME), servicePID);
+        if (!cacheFolder.exists()) {
+            logger.debug("Creating cache folder '{}'", cacheFolder.getAbsolutePath());
+            cacheFolder.mkdirs();
+        }
+        logger.debug("Using cache folder '{}'", cacheFolder.getAbsolutePath());
+
+        if (expiry.isNegative()) {
+            throw new IllegalArgumentException("Cache expiration time must be greater than or equal to 0");
+        }
+        this.expiry = expiry;
+    }
+
+    /**
+     * Adds a file to the cache. If the cache previously contained a file for the key, the old file is replaced by the
+     * new content.
+     *
+     * @param key the key with which the file is to be associated
+     * @param content the content for the file to be associated with the specified key
+     */
+    public void put(String key, byte[] content) {
+        writeFile(getUniqueFile(key), content);
+    }
+
+    /**
+     * Adds a file to the cache.
+     *
+     * @param key the key with which the file is to be associated
+     * @param content the content for the file to be associated with the specified key
+     */
+    public void putIfAbsent(String key, byte[] content) {
+        File fileInCache = getUniqueFile(key);
+        if (fileInCache.exists()) {
+            logger.debug("File '{}' present in cache", fileInCache.getName());
+            // update time of last use
+            fileInCache.setLastModified(System.currentTimeMillis());
+        } else {
+            writeFile(fileInCache, content);
+        }
+    }
+
+    /**
+     * Adds a file to the cache and returns the content of the file.
+     *
+     * @param key the key with which the file is to be associated
+     * @param content the content for the file to be associated with the specified key
+     * @return the content of the file associated with the given key
+     * @throws IOException if an I/O error occurs reading the given file
+     */
+    public byte[] putIfAbsentAndGet(String key, byte[] content) throws IOException {
+        putIfAbsent(key, content);
+
+        return get(key);
+    }
+
+    /**
+     * Writes the given content to the given {@link File}.
+     *
+     * @param fileInCache the {@link File}
+     * @param content the content to be written
+     */
+    private void writeFile(File fileInCache, byte[] content) {
+        logger.debug("Caching file '{}'", fileInCache.getName());
+        try {
+            Files.write(fileInCache.toPath(), content);
+        } catch (IOException e) {
+            logger.warn("Could not write file '{}' to cache", fileInCache.getName(), e);
+        }
+    }
+
+    /**
+     * Checks if the key is present in the cache.
+     *
+     * @param key the key whose presence in the cache is to be tested
+     * @return true if the cache contains a file for the specified key
+     */
+    public boolean containsKey(String key) {
+        return getUniqueFile(key).exists();
+    }
+
+    /**
+     * Removes the file associated with the given key from the cache.
+     *
+     * @param key the key whose associated file is to be removed
+     */
+    public void remove(String key) {
+        deleteFile(getUniqueFile(key));
+    }
+
+    /**
+     * Deletes the given {@link File}.
+     *
+     * @param fileInCache the {@link File}
+     */
+    private void deleteFile(File fileInCache) {
+        if (fileInCache.exists()) {
+            logger.debug("Deleting file '{}' from cache", fileInCache.getName());
+            fileInCache.delete();
+        } else {
+            logger.debug("File '{}' not found in cache", fileInCache.getName());
+        }
+    }
+
+    /**
+     * Removes all files from the cache.
+     */
+    public void clear() {
+        File[] filesInCache = cacheFolder.listFiles();
+        if (filesInCache != null && filesInCache.length > 0) {
+            logger.debug("Deleting all files from cache");
+            Arrays.stream(filesInCache).forEach(File::delete);
+        }
+    }
+
+    /**
+     * Removes expired files from the cache.
+     */
+    public void clearExpired() {
+        // exit if expiry is set to 0 (disabled)
+        if (expiry.isZero() || expiry.isNegative()) {
+            return;
+        }
+        File[] filesInCache = cacheFolder.listFiles();
+        if (filesInCache != null && filesInCache.length > 0) {
+            logger.debug("Deleting expired files from cache");
+            Arrays.stream(filesInCache).filter(this::isExpired).forEach(File::delete);
+        }
+    }
+
+    /**
+     * Checks if the given {@link File} is expired.
+     *
+     * @param fileInCache the {@link File}
+     * @return <code>true</code> if the file is expired, <code>false</code> otherwise
+     */
+    private boolean isExpired(File fileInCache) {
+        // exit if expiry is set to 0 (disabled)
+        long expiryInMillis = expiry.toMillis();
+        return 0 < expiryInMillis && expiryInMillis < System.currentTimeMillis() - fileInCache.lastModified();
+    }
+
+    /**
+     * Returns the content of the file associated with the given key, if it is present.
+     *
+     * @param key the key whose associated file is to be returned
+     * @return the content of the file associated with the given key
+     * @throws FileNotFoundException if the given file could not be found in cache
+     * @throws IOException if an I/O error occurs reading the given file
+     */
+    public byte[] get(String key) throws FileNotFoundException, IOException {
+        return readFile(getUniqueFile(key));
+    }
+
+    /**
+     * Reads the content from the given {@link File}, if it is present.
+     *
+     * @param fileInCache the {@link File}
+     * @return the content of the file
+     * @throws FileNotFoundException if the given file could not be found in cache
+     * @throws IOException if an I/O error occurs reading the given file
+     */
+    private byte[] readFile(File fileInCache) throws FileNotFoundException, IOException {
+        if (fileInCache.exists()) {
+            logger.debug("Reading file '{}' from cache", fileInCache.getName());
+            // update time of last use
+            fileInCache.setLastModified(System.currentTimeMillis());
+            try {
+                return Files.readAllBytes(fileInCache.toPath());
+            } catch (IOException e) {
+                logger.warn("Could not read file '{}' from cache", fileInCache.getName(), e);
+                throw new IOException(String.format("Could not read file '%s' from cache", fileInCache.getName()));
+            }
+        } else {
+            logger.debug("File '{}' not found in cache", fileInCache.getName());
+            throw new FileNotFoundException(String.format("File '%s' not found in cache", fileInCache.getName()));
+        }
+    }
+
+    /**
+     * Creates a unique {@link File} from the key with which the file is to be associated.
+     *
+     * @param key the key with which the file is to be associated
+     * @return unique file for the file associated with the given key
+     */
+    File getUniqueFile(String key) {
+        String uniqueFileName = getUniqueFileName(key);
+        if (filesInCache.containsKey(uniqueFileName)) {
+            return filesInCache.get(uniqueFileName);
+        } else {
+            String fileExtension = getFileExtension(key);
+            File fileInCache = new File(cacheFolder,
+                    uniqueFileName + (fileExtension == null ? "" : EXTENSION_SEPARATOR + fileExtension));
+            filesInCache.put(uniqueFileName, fileInCache);
+            return fileInCache;
+        }
+    }
+
+    /**
+     * Gets the extension of a file name.
+     *
+     * @param fileName the file name to retrieve the extension of
+     * @return the extension of the file or null if none exists
+     */
+    @Nullable
+    String getFileExtension(String fileName) {
+        String strippedFileName = fileName.replaceFirst("\\?.*$", "");
+        int extensionPos = strippedFileName.lastIndexOf(EXTENSION_SEPARATOR);
+        int lastSeparatorPos = strippedFileName.lastIndexOf(File.separator);
+        return lastSeparatorPos > extensionPos ? null : strippedFileName.substring(extensionPos + 1);
+    }
+
+    /**
+     * Creates a unique file name from the key with which the file is to be associated.
+     *
+     * @param key the key with which the file is to be associated
+     * @return unique file name for the file associated with the given key
+     */
+    String getUniqueFileName(String key) {
+        return String.format("%032x", BigInteger.valueOf(key.hashCode()));
+    }
+}

bundles/org.openhab.core/src/test/java/org/openhab/core/cache/ByteArrayFileCacheTest.java

@@ -0,0 +1,238 @@
+/**
+ * Copyright (c) 2010-2020 Contributors to the openHAB project
+ *
+ * See the NOTICE file(s) distributed with this work for additional
+ * information.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License 2.0 which is available at
+ * http://www.eclipse.org/legal/epl-2.0
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ */
+package org.openhab.core.cache;
+
+import static org.hamcrest.CoreMatchers.*;
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import java.io.File;
+import java.io.FileNotFoundException;
+import java.io.IOException;
+import java.nio.file.Files;
+import java.time.Duration;
+
+import org.eclipse.jdt.annotation.NonNullByDefault;
+import org.eclipse.jdt.annotation.Nullable;
+import org.junit.jupiter.api.AfterAll;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.openhab.core.OpenHAB;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Test class for the {@link ByteArrayFileCache} class.
+ *
+ * @author Christoph Weitkamp - Initial contribution
+ */
+@NonNullByDefault
+public class ByteArrayFileCacheTest {
+
+    private static final String SERVICE_PID = "org.openhab.core.test";
+
+    private static final File USERDATA_FOLDER = new File(OpenHAB.getUserDataFolder());
+    private static final File CACHE_FOLDER = new File(USERDATA_FOLDER, ByteArrayFileCache.CACHE_FOLDER_NAME);
+    private static final File SERVICE_CACHE_FOLDER = new File(CACHE_FOLDER, SERVICE_PID);
+
+    private static final String MP3_FILE_NAME = SERVICE_CACHE_FOLDER.getAbsolutePath() + "doorbell.mp3";
+    private static final String TXT_FILE_NAME = SERVICE_CACHE_FOLDER.getAbsolutePath() + "doorbell.txt";
+
+    private static @Nullable File txtFile;
+
+    private final Logger logger = LoggerFactory.getLogger(ByteArrayFileCacheTest.class);
+
+    private @NonNullByDefault({}) ByteArrayFileCache subject;
+
+    @BeforeAll
+    public static void init() throws IOException {
+        // create temporary file
+        txtFile = createTempTxtFile();
+    }
+
+    @BeforeEach
+    public void setUp() {
+        subject = new ByteArrayFileCache(SERVICE_PID);
+    }
+
+    @AfterEach
+    public void tearDown() {
+        // delete all files
+        subject.clear();
+    }
+
+    @AfterAll
+    public static void cleanUp() {
+        // delete all folders
+        SERVICE_CACHE_FOLDER.delete();
+        CACHE_FOLDER.delete();
+        USERDATA_FOLDER.delete();
+    }
+
+    @Test
+    public void testGetFileExtension() {
+        assertThat(subject.getFileExtension("/var/log/openhab/"), is(nullValue()));
+        assertThat(subject.getFileExtension("/var/log/foo.bar/"), is(nullValue()));
+        assertThat(subject.getFileExtension("doorbell.mp3"), is(equalTo("mp3")));
+        assertThat(subject.getFileExtension("/tmp/doorbell.mp3"), is(equalTo("mp3")));
+        assertThat(subject.getFileExtension(MP3_FILE_NAME), is(equalTo("mp3")));
+        assertThat(subject.getFileExtension(TXT_FILE_NAME), is(equalTo("txt")));
+        assertThat(subject.getFileExtension("/var/log/openhab/.."), is(""));
+        assertThat(subject.getFileExtension(".hidden"), is(equalTo("hidden")));
+        assertThat(subject.getFileExtension("C:\\Program Files (x86)\\java\\bin\\javaw.exe"), is(equalTo("exe")));
+        assertThat(subject.getFileExtension("https://www.youtube.com/watch?v=qYrpPrLY868"), is(nullValue()));
+        assertThat(subject.getFileExtension("https://www.youtube.com/watch?v=Test.With.Dots"), is(nullValue()));
+        assertThat(subject.getFileExtension("https://host/test.xlsx?cache=false"), is("xlsx"));
+        // assertThat(subject.getFileExtension(
+        // "http://127.0.0.1:8080/image/image%3A%2F%2Fhttp%253a%252f%252f127.0.0.1%253a32400%252fphoto%252f%253a%252ftranscode%253fwidth%253d1920%2526height%253d1920%2526minSize%253d1%2526upscale%253d0%2526url%253d%252flibrary%252fmetadata%252f1896%252fthumb%252f1569782004%2526X-Plex-Token%253dXScJLJbUdcybNXFyHLuv"),
+        // is(nullValue()));
+    }
+
+    @Test
+    public void testGetUniqueFileName() {
+        String mp3UniqueFileName = subject.getUniqueFileName(MP3_FILE_NAME);
+        assertThat(mp3UniqueFileName, is(equalTo(subject.getUniqueFileName(MP3_FILE_NAME))));
+
+        String txtUniqueFileName = subject.getUniqueFileName(TXT_FILE_NAME);
+        assertThat(txtUniqueFileName, is(equalTo(subject.getUniqueFileName(TXT_FILE_NAME))));
+
+        assertThat(mp3UniqueFileName, is(not(equalTo(txtUniqueFileName))));
+    }
+
+    @Test
+    public void testGet() {
+        assertThrows(FileNotFoundException.class, () -> subject.get(TXT_FILE_NAME));
+    }
+
+    @Test
+    public void testPut() throws IOException {
+        byte[] buffer = readTempTxtFile();
+        subject.put(TXT_FILE_NAME, buffer);
+
+        assertThat(subject.get(TXT_FILE_NAME), is(equalTo(buffer)));
+    }
+
+    @Test
+    public void testPutIfAbsentAddsANewFile() throws IOException {
+        byte[] buffer = readTempTxtFile();
+        subject.putIfAbsent(TXT_FILE_NAME, buffer);
+
+        assertThat(subject.get(TXT_FILE_NAME), is(equalTo(buffer)));
+    }
+
+    @Test
+    public void testPutIfAbsentDoesNotOverwriteExistingFile() throws IOException {
+        byte[] buffer = readTempTxtFile();
+        subject.putIfAbsent(TXT_FILE_NAME, buffer);
+        subject.putIfAbsent(TXT_FILE_NAME, TXT_FILE_NAME.getBytes());
+
+        assertThat(subject.get(TXT_FILE_NAME), is(equalTo(buffer)));
+    }
+
+    @Test
+    public void testPutIfAbsentAndGetAddsANewFile() throws IOException {
+        byte[] buffer = readTempTxtFile();
+
+        assertThat(subject.putIfAbsentAndGet(TXT_FILE_NAME, buffer), is(equalTo(buffer)));
+    }
+
+    @Test
+    public void testPutIfAbsentAndGetDoesNotOverwriteExistingFile() throws IOException {
+        byte[] buffer = readTempTxtFile();
+
+        subject.putIfAbsentAndGet(TXT_FILE_NAME, buffer);
+        assertThat(subject.putIfAbsentAndGet(TXT_FILE_NAME, TXT_FILE_NAME.getBytes()), is(equalTo(buffer)));
+    }
+
+    @Test
+    public void testContainsKey() {
+        assertThat(subject.containsKey(TXT_FILE_NAME), is(false));
+
+        subject.put(TXT_FILE_NAME, readTempTxtFile());
+
+        assertThat(subject.containsKey(TXT_FILE_NAME), is(true));
+    }
+
+    @Test
+    public void testRemove() {
+        subject.put(TXT_FILE_NAME, readTempTxtFile());
+        subject.remove(TXT_FILE_NAME);
+
+        assertThrows(FileNotFoundException.class, () -> subject.get(TXT_FILE_NAME));
+    }
+
+    @Test
+    public void testClear() {
+        subject.put(TXT_FILE_NAME, readTempTxtFile());
+        subject.clear();
+
+        assertThrows(FileNotFoundException.class, () -> subject.get(TXT_FILE_NAME));
+    }
+
+    @Test
+    public void clearExpiredClearsNothingIfExpiryNotSet() throws IOException {
+        byte[] buffer = readTempTxtFile();
+        subject.put(TXT_FILE_NAME, buffer);
+        subject.clearExpired();
+
+        assertThat(subject.get(TXT_FILE_NAME), is(equalTo(buffer)));
+    }
+
+    @Test
+    public void clearExpiredClearsNothingIfNotExpired() throws IOException {
+        subject = new ByteArrayFileCache(SERVICE_PID, Duration.ofSeconds(5));
+
+        byte[] buffer = readTempTxtFile();
+        subject.put(TXT_FILE_NAME, buffer);
+        subject.clearExpired();
+
+        assertThat(subject.get(TXT_FILE_NAME), is(equalTo(buffer)));
+    }
+
+    @Test
+    public void clearExpiredIfExpired() {
+        Duration expiry = Duration.ofSeconds(5);
+        subject = new ByteArrayFileCache(SERVICE_PID, expiry);
+
+        subject.put(TXT_FILE_NAME, readTempTxtFile());
+
+        // manipulate time of last use
+        File fileInCache = subject.getUniqueFile(TXT_FILE_NAME);
+        fileInCache.setLastModified(System.currentTimeMillis() - 2 * expiry.toMillis());
+
+        subject.clearExpired();
+
+        assertThrows(FileNotFoundException.class, () -> subject.get(TXT_FILE_NAME));
+    }
+
+    private static File createTempTxtFile() throws IOException {
+        final File file = File.createTempFile("doorbell", "txt");
+        file.deleteOnExit();
+        return file;
+    }
+
+    private byte[] readTempTxtFile() {
+        if (txtFile != null) {
+            try {
+                return Files.readAllBytes(txtFile.toPath());
+            } catch (IOException e) {
+                logger.error("Error while reading temp file");
+            }
+        } else {
+            logger.error("Temp file not found");
+        }
+        return new byte[0];
+    }
+}

bundles/org.openhab.core/src/test/java/org/openhab/core/cache/ExpiringCacheMapTest.java

@@ -23,6 +23,8 @@ import java.util.Set;
 import java.util.concurrent.TimeUnit;
 import java.util.function.Supplier;
 
+import org.eclipse.jdt.annotation.NonNullByDefault;
+import org.eclipse.jdt.annotation.Nullable;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
@@ -32,24 +34,25 @@ import org.junit.jupiter.api.Test;
  * @author Christoph Weitkamp - Initial contribution
  * @author Martin van Wingerden - Added tests for putIfAbsentAndGet
  */
+@NonNullByDefault
 public class ExpiringCacheMapTest {
     private static final long CACHE_EXPIRY = TimeUnit.SECONDS.toMillis(2);
 
     private static final String RESPONSE_1 = "ACTION 1";
     private static final String RESPONSE_2 = "ACTION 2";
 
-    private static final Supplier<String> CACHE_ACTION = () -> {
+    private static final Supplier<@Nullable String> CACHE_ACTION = () -> {
         byte[] array = new byte[8];
         new Random().nextBytes(array);
         return new String(array, StandardCharsets.UTF_8);
     };
-    private static final Supplier<String> PREDICTABLE_CACHE_ACTION_1 = () -> RESPONSE_1;
+    private static final Supplier<@Nullable String> PREDICTABLE_CACHE_ACTION_1 = () -> RESPONSE_1;
-    private static final Supplier<String> PREDICTABLE_CACHE_ACTION_2 = () -> RESPONSE_2;
+    private static final Supplier<@Nullable String> PREDICTABLE_CACHE_ACTION_2 = () -> RESPONSE_2;
 
     private static final String FIRST_TEST_KEY = "FIRST_TEST_KEY";
     private static final String SECOND_TEST_KEY = "SECOND_TEST_KEY";
 
-    private ExpiringCacheMap<String, String> subject;
+    private @NonNullByDefault({}) ExpiringCacheMap<String, String> subject;
 
     @BeforeEach
     public void setUp() {
@@ -139,13 +142,15 @@ public class ExpiringCacheMapTest {
         assertNotNull(value3);
         assertNotEquals(value1, value3);
 
-        // get all values
+        if (value1 != null && value3 != null) {
-        final Collection<String> expectedValues = new LinkedList<>();
+            // get all values
-        expectedValues.add(value3);
+            final Collection<String> expectedValues = new LinkedList<>();
-        expectedValues.add(value1);
+            expectedValues.add(value3);
+            expectedValues.add(value1);
 
-        final Collection<String> values = subject.values();
+            final Collection<@Nullable String> values = subject.values();
-        assertEquals(expectedValues, values);
+            assertEquals(expectedValues, values);
+        }
 
         // use another different key
         String value4 = subject.get("KEY_NOT_FOUND");
@@ -192,14 +197,17 @@ public class ExpiringCacheMapTest {
 
         // refresh item
         String value2 = subject.refresh(FIRST_TEST_KEY);
+        assertNotNull(value2);
         assertNotEquals(value1, value2);
 
-        // refresh all
+        if (value2 != null) {
-        final Collection<String> expectedValues = new LinkedList<>();
+            // refresh all
-        expectedValues.add(value2);
+            final Collection<String> expectedValues = new LinkedList<>();
+            expectedValues.add(value2);
 
-        final Collection<String> values = subject.refreshAll();
+            final Collection<@Nullable String> values = subject.refreshAll();
-        assertNotEquals(expectedValues, values);
+            assertNotEquals(expectedValues, values);
+        }
     }
 
     @Test

bundles/org.openhab.core/src/test/java/org/openhab/core/cache/ExpiringCacheTest.java

@@ -19,6 +19,8 @@ import java.util.Random;
 import java.util.concurrent.TimeUnit;
 import java.util.function.Supplier;
 
+import org.eclipse.jdt.annotation.NonNullByDefault;
+import org.eclipse.jdt.annotation.Nullable;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
@@ -27,15 +29,17 @@ import org.junit.jupiter.api.Test;
  *
  * @author Christoph Weitkamp - Initial contribution
  */
+@NonNullByDefault
 public class ExpiringCacheTest {
     private static final long CACHE_EXPIRY = TimeUnit.SECONDS.toMillis(2);
-    private static final Supplier<String> CACHE_ACTION = () -> {
+
+    private static final Supplier<@Nullable String> CACHE_ACTION = () -> {
         byte[] array = new byte[8];
         new Random().nextBytes(array);
         return new String(array, StandardCharsets.UTF_8);
     };
 
-    private ExpiringCache<String> subject;
+    private @NonNullByDefault({}) ExpiringCache<String> subject;
 
     @BeforeEach
     public void setUp() {