support loading properties file in unnamed resources module. (#1827)

src/main/java/com/zaxxer/hikari/HikariConfig.java

@@ -26,9 +26,7 @@
 import javax.naming.InitialContext;
 import javax.naming.NamingException;
 import javax.sql.DataSource;
-import java.io.File;
-import java.io.FileInputStream;
-import java.io.IOException;
+import java.io.*;
 import java.lang.reflect.Modifier;
 import java.security.AccessControlException;
 import java.sql.Connection;
@@ -1199,8 +1197,7 @@ else if (value == null) {
 
    private void loadProperties(String propertyFileName)
    {
-      final var propFile = new File(propertyFileName);
-      try (final var is = propFile.isFile() ? new FileInputStream(propFile) : this.getClass().getResourceAsStream(propertyFileName)) {
+      try (final var is = openPropertiesInputStream(propertyFileName)) {
          if (is != null) {
             var props = new Properties();
             props.load(is);
@@ -1215,6 +1212,18 @@ private void loadProperties(String propertyFileName)
       }
    }
 
+   private InputStream openPropertiesInputStream(String propertyFileName) throws FileNotFoundException {
+      final var propFile = new File(propertyFileName);
+      if (propFile.isFile()) {
+         return new FileInputStream(propFile);
+      }
+      var propertiesInputStream = this.getClass().getResourceAsStream(propertyFileName);
+      if (propertiesInputStream == null) {
+        propertiesInputStream = this.getClass().getClassLoader().getResourceAsStream(propertyFileName);
+      }
+      return propertiesInputStream;
+   }
+
    private String generatePoolName()
    {
       final var prefix = "HikariPool-";