HttpResource

+    package de.juplo.httpresources;
+
+    import org.springframework.http.HttpHeaders;
+    import org.springframework.util.MimeType;
+
+    import java.io.*;
+    import java.net.URI;
+    import java.net.URL;
+    import java.time.Clock;
+    import java.util.Objects;
+
+
+    public class HttpResource implements org.springframework.web.servlet.resource.HttpResource
+    {
+      final HttpResources resources;
+      final HttpResourceFetcher fetcher;
+      final Clock clock;
+      final URI uri;
+
+      HttpData data;
+      boolean modified;
+
+      HttpResource(
+          HttpResources resources,
+          HttpResourceFetcher fetcher,
+          Clock clock,
+          URI uri)
+      {
+        this(resources, fetcher, clock, uri, HttpData.NOT_FETCHED);
+      }
+
+      HttpResource(
+            HttpResources resources,
+            HttpResourceFetcher fetcher,
+            Clock clock,
+            URI uri,
+            HttpData data)
+        {
+        this.resources = resources;
+        this.fetcher = fetcher;
+        this.clock = clock;
+        this.uri = uri;
+        this.data = data;
+      }
+
+
+      synchronized public long expires()
+      {
+        return data.expires;
+      }
+
+      synchronized public boolean isExpired()
+      {
+        return data.expires < clock.millis();
+      }
+
+      @Override
+      synchronized public boolean exists()
+      {
+        if (isExpired())
+          fetch();
+        return data.content != null;
+      }
+
+      @Override
+      synchronized public boolean isReadable()
+      {
+        return exists();
+      }
+
+      @Override
+      public boolean isOpen()
+      {
+        return false;
+      }
+
+      @Override
+      public URL getURL() throws IOException
+      {
+        return uri.toURL();
+      }
+
+      @Override
+      public URI getURI()
+      {
+        return uri;
+      }
+
+      @Override
+      public File getFile() throws IOException
+      {
+        throw new FileNotFoundException("The resource " + getDescription() + " cannot be retrived as file");
+      }
+
+      @Override
+      synchronized public long contentLength() throws IOException
+      {
+        if (!fetched())
+          fetch();
+
+        if (data.content == null)
+          throw new FileNotFoundException("The resource " + getDescription() + " cannot be retrived");
+
+        return data.content.length;
+      }
+
+      synchronized public MimeType contentType()
+      {
+        return data.headers.getContentType();
+      }
+
+      @Override
+      synchronized public long lastModified() throws IOException
+      {
+        if (!fetched())
+          fetch();
+
+        if (data.content == null)
+          throw new FileNotFoundException("The resource " + getDescription() + " cannot be retrived");
+
+        return data.lastModified;
+      }
+
+      synchronized public String eTag()
+      {
+        return data.eTag;
+      }
+
+      @Override
+      public HttpResource createRelative(String relativePath) throws IOException
+      {
+        try
+        {
+          return createRelative(HttpResources.convert(relativePath));
+        }
+        catch (IllegalArgumentException e)
+        {
+          throw new IOException("Invalid relative path: " + relativePath, e);
+        }
+      }
+
+      public HttpResource createRelative(URI relative) throws IOException
+      {
+        return resources.getResource(HttpResources.resolve(relative, uri));
+      }
+
+      @Override
+      public String getFilename()
+      {
+        return uri.getPath();
+      }
+
+      @Override
+      public String getDescription()
+      {
+        return "HTTP [" + this.uri + "]";
+      }
+
+      @Override
+      synchronized public InputStream getInputStream() throws IOException
+      {
+        if (!fetched())
+        {
+          fetch();
+        }
+        else
+        {
+          isModified();
+        }
+
+        // Clear the modified-flag
+        modified = false;
+
+        if (data.content == null)
+          throw new FileNotFoundException("The resource " + getDescription() + " cannot be retrived as file");
+
+        return new ByteArrayInputStream(data.content);
+      }
+
+      synchronized public boolean isModified()
+      {
+        if (modified)
+        {
+          return true;
+        }
+
+        if (!isExpired())
+        {
+          return false;
+        }
+
+        return fetch();
+      }
+
+      /**
+       * Checks, if the remote resource was already fetched.
+       *
+       * @return {@code true}, if the resource was already fetched, otherwise
+       * {@code false}
+       */
+      synchronized public boolean fetched()
+      {
+        return data.expires != Long.MIN_VALUE;
+      }
+
+      /**
+       * Fetches the remote resource and reports, if it was modified.
+       * <p>
+       * This method fetches the remote resource, if was not already fetched.
+       * If the resource was already fetched, it revalidates it, if necessary.
+       *
+       * @return {@code true}, if the resource has changed or was fetched for
+       * the first time, otherwise {@code false}
+       */
+      synchronized public boolean fetch()
+      {
+        HttpData result = fetcher.fetch(uri, data);
+
+        // Flag the resource as modified, if the data has changed
+        // Otherwise, keep the old state of the modified-flag.
+        modified = !data.equals(result);
+
+        data = result;
+
+        return modified;
+      }
+
+      @Override
+      synchronized public HttpHeaders getResponseHeaders()
+      {
+        return data.headers;
+      }
+
+
+      @Override
+      public int hashCode()
+      {
+        return uri.hashCode();
+      }
+
+      @Override
+      public boolean equals(Object o)
+      {
+        if (o == null)
+          return false;
+        if (o == this)
+          return true;
+        if (!(o instanceof HttpResource))
+          return false;
+        return Objects.equals(uri, ((HttpResource) o).uri);
+      }
+
+      @Override
+      public String toString()
+      {
+        return getDescription();
+      }
+    }
+