Add support for loading kafka properties from classpath (#637)

* Add support for loading kafka properties from classpath

* Silently ignore missing but configured property file

* Refactor code

* Improve variable name

---------

Co-authored-by: Alvin Kwekel <[email protected]>

src/main/java/kafdrop/config/KafkaConfiguration.java

@@ -1,18 +1,22 @@
 package kafdrop.config;
 
 import lombok.Data;
+import org.apache.commons.lang3.StringUtils;
 import org.apache.kafka.clients.CommonClientConfigs;
-import org.apache.kafka.common.config.SaslConfigs;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 import org.springframework.boot.context.properties.ConfigurationProperties;
+import org.springframework.core.io.AbstractResource;
+import org.springframework.core.io.ClassPathResource;
+import org.springframework.core.io.FileSystemResource;
+import org.springframework.core.io.Resource;
 import org.springframework.stereotype.Component;
 
-import java.io.BufferedReader;
 import java.io.File;
-import java.io.FileReader;
 import java.io.IOException;
+import java.util.Optional;
 import java.util.Properties;
+import java.util.stream.Stream;
 
 
 @Component
@@ -48,12 +52,16 @@ public void applyCommon(Properties properties) {
     }
 
     LOG.info("Checking properties file {}", propertiesFile);
-    final var propertiesFile = new File(this.propertiesFile);
-    if (propertiesFile.isFile()) {
-      LOG.info("Loading properties from {}", this.propertiesFile);
+    Optional<AbstractResource> propertiesResource = StringUtils.isBlank(propertiesFile) ? Optional.empty() :
+      Stream.of(new FileSystemResource(propertiesFile),
+          new ClassPathResource(propertiesFile))
+        .filter(Resource::isReadable)
+        .findFirst();
+    if (propertiesResource.isPresent()) {
+      LOG.info("Loading properties from {}", propertiesFile);
       final var propertyOverrides = new Properties();
-      try (var propsReader = new BufferedReader(new FileReader(propertiesFile))) {
-        propertyOverrides.load(propsReader);
+      try {
+        propertyOverrides.load(propertiesResource.get().getInputStream());
       } catch (IOException e) {
         throw new KafkaConfigurationException(e);
       }