HttpResourceChainAwareResourceLoader

+    package de.juplo.httpresources;
+
+    import org.slf4j.Logger;
+    import org.slf4j.LoggerFactory;
+    import org.springframework.core.io.Resource;
+    import org.springframework.core.io.ResourceLoader;
+
+    import java.util.Arrays;
+
+    public class HttpResourceChainAwareResourceLoader implements ResourceLoader
+    {
+      private static final Logger LOG =
+          LoggerFactory.getLogger(HttpResourceChainAwareResourceLoader.class);
+
+
+      private final ResourceLoader loader;
+      private final String[] sources;
+
+
+
+      public HttpResourceChainAwareResourceLoader(
+          ResourceLoader loader,
+          String... sources)
+      {
+        this.loader = loader;
+        this.sources =
+            Arrays
+                .stream(sources)
+                .map(location -> location.trim())
+                .filter(location ->
+                {
+                  if (location.length() > 0)
+                    return true;
+
+                  LOG.warn("Filtered out empty entry from list of sources");
+                  return false;
+                })
+                .map(location ->
+                {
+                  int length = location.length();
+                  if (length > 0 && location.charAt(length - 1) != '/')
+                  {
+                    LOG.info("Adding trailing slash to configured source {}", location);
+                    return location + "/";
+                  }
+                  else
+                    return location;
+                })
+                .toArray(size -> new String[size]);
+      }
+
+
+      /**
+       * Returns the first existing resource, or the first, if non of the
+       * resources exists.
+       *
+       * This mimics the behavior of the original resolver as closeley as possible,
+       * asuming, that the first source is a / the local one.
+       *
+       * @param location The name of the requested resource
+       * @return The first existing resource, or the first resource - never <code>null</code>.
+       */
+      @Override
+      public Resource getResource(String location)
+      {
+        // We assure in the constructore, that sources always end with a '/'
+        String relativeResourceName =
+            location.charAt(0) == '/'
+                ? location.substring(1)
+                : location;
+
+        for (String source : sources)
+        {
+          Resource resource = loader.getResource(source + relativeResourceName);
+
+          // Return the resource, if it exists.
+          if (resource.exists())
+            return resource;
+        }
+
+        // If all sources were checked without success, return the resource from
+        // the first source, although it does not exists - the contract of an
+        // {@link ResourceLoader} requires, that the return-value is neve {@code null}.
+        // Therefore, we fall back to the behaviour of our parent-loader.
+        return loader.getResource(location);
+      }
+
+      @Override
+      public ClassLoader getClassLoader()
+      {
+        return loader.getClassLoader();
+      }
+    }
+