Merge pull request #1716 from ManuelB/jenkins-1.614-branch-JJI-188

 [JENKINS-28553] Stable workaround for adding PluginServletFilter

core/src/main/java/hudson/util/PluginServletFilter.java

@@ -27,6 +27,7 @@ import hudson.ExtensionPoint;
 import hudson.security.SecurityRealm;
 import jenkins.model.Jenkins;
 
+import javax.annotation.CheckForNull;
 import javax.servlet.Filter;
 import javax.servlet.FilterChain;
 import javax.servlet.FilterConfig;
@@ -71,8 +72,11 @@ public class PluginServletFilter implements Filter, ExtensionPoint {
 
     /**
      * Lookup the instance from servlet context.
+     *
+     * @param c the ServletContext most of the time taken from a Jenkins instance
+     * @return get the current PluginServletFilter if it is already available
      */
-    private static PluginServletFilter getInstance(ServletContext c) {
+    private static @CheckForNull PluginServletFilter getInstance(ServletContext c) {
         return (PluginServletFilter)c.getAttribute(KEY);
     }
 
@@ -90,12 +94,17 @@ public class PluginServletFilter implements Filter, ExtensionPoint {
 
     public static void addFilter(Filter filter) throws ServletException {
         Jenkins j = Jenkins.getInstance();
-        if (j==null) {
+        
+        PluginServletFilter container = null;
+        if(j != null) {
+            container = getInstance(j.servletContext);
+	}
+        // https://marvelution.atlassian.net/browse/JJI-188
+        if (j==null || container == null) {
             // report who is doing legacy registration
             LOGGER.log(Level.WARNING, "Filter instance is registered too early: "+filter, new Exception());
             LEGACY.add(filter);
         } else {
-            PluginServletFilter container = getInstance(j.servletContext);
             filter.init(container.config);
             container.list.add(filter);
         }
@@ -103,7 +112,7 @@ public class PluginServletFilter implements Filter, ExtensionPoint {
 
     public static void removeFilter(Filter filter) throws ServletException {
         Jenkins j = Jenkins.getInstance();
-        if (j==null) {
+        if (j==null || getInstance(j.servletContext) == null) {
             LEGACY.remove(filter);
         } else {
             getInstance(j.servletContext).list.remove(filter);