Improve locating config files (#4560)

(cherry picked from commit f34455b)

Author: lhotari

bookkeeper-server/src/main/java/org/apache/bookkeeper/bookie/storage/ldb/KeyValueStorageRocksDB.java

@@ -40,6 +40,7 @@
 import java.util.concurrent.TimeUnit;
 import org.apache.bookkeeper.bookie.storage.ldb.KeyValueStorageFactory.DbConfigType;
 import org.apache.bookkeeper.conf.ServerConfiguration;
+import org.apache.commons.lang3.StringUtils;
 import org.rocksdb.BlockBasedTableConfig;
 import org.rocksdb.BloomFilter;
 import org.rocksdb.Cache;
@@ -131,7 +132,7 @@ public KeyValueStorageRocksDB(String basePath, String subPath, DbConfigType dbCo
             dbFilePath = conf.getDefaultRocksDBConf();
         }
         log.info("Searching for a RocksDB configuration file in {}", dbFilePath);
-        if (Paths.get(dbFilePath).toFile().exists()) {
+        if (StringUtils.isNotBlank(dbFilePath) && Paths.get(dbFilePath).toFile().exists()) {
             log.info("Found a RocksDB configuration file and using it to initialize the RocksDB");
             db = initializeRocksDBWithConfFile(basePath, subPath, dbConfigType, conf, readOnly, dbFilePath);
         } else {

bookkeeper-server/src/main/java/org/apache/bookkeeper/conf/ServerConfiguration.java

@@ -25,6 +25,7 @@
 import java.io.File;
 import java.net.URL;
 import java.util.concurrent.TimeUnit;
+import lombok.SneakyThrows;
 import org.apache.bookkeeper.bookie.FileChannelProvider;
 import org.apache.bookkeeper.bookie.InterleavedLedgerStorage;
 import org.apache.bookkeeper.bookie.LedgerStorage;
@@ -4047,12 +4048,7 @@ public boolean isSkipReplayJournalInvalidRecord() {
      * @return String configured default rocksdb conf.
      */
     public String getDefaultRocksDBConf() {
-        String defaultPath = "conf/default_rocksdb.conf";
-        URL defURL = getClass().getClassLoader().getResource(defaultPath);
-        if (defURL != null) {
-            defaultPath = defURL.getPath();
-        }
-        return getString(DEFAULT_ROCKSDB_CONF, defaultPath);
+        return getString(DEFAULT_ROCKSDB_CONF, getDefaultFilePath("conf/default_rocksdb.conf"));
     }
 
     /**
@@ -4071,12 +4067,7 @@ public ServerConfiguration setDefaultRocksDBConf(String defaultRocksdbConf) {
      * @return String configured entry Location rocksdb conf.
      */
     public String getEntryLocationRocksdbConf() {
-        String defaultPath = "conf/entry_location_rocksdb.conf";
-        URL defURL = getClass().getClassLoader().getResource(defaultPath);
-        if (defURL != null) {
-            defaultPath = defURL.getPath();
-        }
-        return getString(ENTRY_LOCATION_ROCKSDB_CONF, defaultPath);
+        return getString(ENTRY_LOCATION_ROCKSDB_CONF, getDefaultFilePath("conf/entry_location_rocksdb.conf"));
     }
 
     /**
@@ -4095,12 +4086,7 @@ public ServerConfiguration setEntryLocationRocksdbConf(String entryLocationRocks
      * @return String configured ledger metadata rocksdb conf.
      */
     public String getLedgerMetadataRocksdbConf() {
-        String defaultPath = "conf/ledger_metadata_rocksdb.conf";
-        URL defURL = getClass().getClassLoader().getResource(defaultPath);
-        if (defURL != null) {
-            defaultPath = defURL.getPath();
-        }
-        return getString(LEDGER_METADATA_ROCKSDB_CONF, defaultPath);
+        return getString(LEDGER_METADATA_ROCKSDB_CONF, getDefaultFilePath("conf/ledger_metadata_rocksdb.conf"));
     }
 
     /**
@@ -4133,4 +4119,28 @@ public ServerConfiguration setOperationMaxNumbersInSingleRocksDBWriteBatch(int m
     public int getMaxOperationNumbersInSingleRocksDBBatch() {
         return getInt(MAX_OPERATION_NUMBERS_IN_SINGLE_ROCKSDB_WRITE_BATCH, 100000);
     }
+
+    /**
+     * Retrieves the default file path for the specified file name.
+     * This method prioritizes a file available in the classpath, which is often used in testing scenarios.
+     * If the file is not found in the classpath, the original file name is returned.
+     *
+     * @param fileName the name of the file for which to retrieve the path.
+     * @return the path of the file if found in the classpath, otherwise the input file name.
+     */
+    @SneakyThrows
+    private String getDefaultFilePath(String fileName) {
+        // Attempt to locate the file in the classpath, used mainly for testing purposes.
+        URL resourceURL = getClass().getClassLoader().getResource(fileName);
+        if (resourceURL != null && "file".equals(resourceURL.getProtocol())) {
+            // Convert the URL to a File object using toURI() for proper URL decoding
+            // and platform specific file path handling (such as on Windows OS)
+            File file = new File(resourceURL.toURI());
+            if (file.exists()) {
+                return file.getAbsolutePath();
+            }
+        }
+        // Return the original file name if no path was found in the classpath
+        return fileName;
+    }
 }