added cache-control header to api response, to fix stale data on ie11

scm-webapp/src/main/java/sonia/scm/api/v2/CacheControlResponseFilter.java

@@ -0,0 +1,39 @@
+package sonia.scm.api.v2;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import javax.ws.rs.container.ContainerRequestContext;
+import javax.ws.rs.container.ContainerResponseContext;
+import javax.ws.rs.container.ContainerResponseFilter;
+import javax.ws.rs.ext.Provider;
+
+/**
+ * Adds the Cache-Control: no-cache header to every api call. But only if non caching headers are set to the response.
+ * The Cache-Control header should fix stale resources on ie.
+ */
+@Provider
+public class CacheControlResponseFilter implements ContainerResponseFilter {
+
+  private static final Logger LOG = LoggerFactory.getLogger(CacheControlResponseFilter.class);
+
+  @Override
+  public void filter(ContainerRequestContext requestContext, ContainerResponseContext responseContext) {
+    if (!isCacheable(responseContext)) {
+      LOG.trace("add no-cache header to response");
+      responseContext.getHeaders().add("Cache-Control", "no-cache");
+    }
+  }
+
+  private boolean isCacheable(ContainerResponseContext responseContext) {
+    return hasLastModifiedDate(responseContext) || hasEntityTag(responseContext);
+  }
+
+  private boolean hasEntityTag(ContainerResponseContext responseContext) {
+    return responseContext.getEntityTag() != null;
+  }
+
+  private boolean hasLastModifiedDate(ContainerResponseContext responseContext) {
+    return responseContext.getLastModified() != null;
+  }
+}