Add backends by id request.

src/main/java/ch/psi/daq/queryrest/controller/QueryRestController.java

@@ -4,8 +4,10 @@ import java.net.URLDecoder;
 import java.nio.charset.StandardCharsets;
 import java.util.Arrays;
 import java.util.List;
+import java.util.Map;
 import java.util.Map.Entry;
 import java.util.Set;
+import java.util.function.Function;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
@@ -130,7 +132,7 @@ public class QueryRestController implements ApplicationContextAware {
       if (request == null) {
          request = new ChannelsRequest();
       }
-      
+
       ((AbstractHTTPResponse) defaultResponse).respond(
             context,
             res,
@@ -166,7 +168,7 @@ public class QueryRestController implements ApplicationContextAware {
       if (request == null) {
          request = new ChannelConfigurationsRequest();
       }
-      
+
       ((AbstractHTTPResponse) defaultResponse).respond(
             context,
             res,
@@ -517,6 +519,23 @@ public class QueryRestController implements ApplicationContextAware {
             .collect(Collectors.toList());
    }
 
+   /**
+    * Returns the current mapping of id to {@link Backend}.
+    * 
+    * @return id to {@link Backend}s mapping
+    */
+   @RequestMapping(
+         value = DomainConfig.PATH_BACKENDS + "/byid",
+         method = {RequestMethod.GET},
+         produces = {MediaType.APPLICATION_JSON_VALUE})
+   public @ResponseBody Map<Integer, Backend> getBackendValuesById() {
+      return Backend.getBackends().stream()
+            .filter(backend -> activeBackends.contains(backend))
+            .collect(Collectors.toMap(
+                  Backend::getId,
+                  Function.identity()));
+   }
+
    /**
     * Returns the current list of {@link Compression}s available.
     *