com.sap.cloud.sdk.frameworks.hystrix.ScpNeoHystrix

Question

If I use ODataQueryBuilder in a servlet, I can call the servlet without any problem.

If I incorporated the code in a method and call this method within a ServletContextListener, I got first the following error.

2018 02 27 13:17:09#+00#ERROR#org.apache.catalina.core.ContainerBase.[Catalina].[localhost].[/]##anonymous#fs-watcher#na#afc186d33#firstapp#web##na#na#na#na#Exception sending context initialized event to listener instance of class com.sap.cloud.sdk.frameworks.hystrix.ScpNeoHystrixBootstrapListenerjava.lang.IllegalStateException: Another strategy was already registered.
at com.netflix.hystrix.strategy.HystrixPlugins.registerConcurrencyStrategy(HystrixPlugins.java:190)
at com.sap.cloud.sdk.frameworks.hystrix.ScpNeoHystrixBootstrapListener.bootstrap(ScpNeoHystrixBootstrapListener.java:43)
at com.sap.cloud.sdk.frameworks.hystrix.ScpNeoHystrixBootstrapListener.contextInitialized(ScpNeoHystrixBootstrapListener.java:74)
at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:5110)
at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5633)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:145)
at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:1015)
at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:991)
at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:652)
at org.eclipse.gemini.web.tomcat.internal.TomcatServletContainer.startWebApplication(TomcatServletContainer.java:125)
at org.eclipse.gemini.web.internal.StandardWebApplication.start(StandardWebApplication.java:109)
at org.eclipse.gemini.web.extender.WebContainerBundleCustomizer.addingBundle(WebContainerBundleCustomizer.java:49)
at org.osgi.util.tracker.BundleTracker$Tracked.customizerAdding(BundleTracker.java:467)
at org.osgi.util.tracker.BundleTracker$Tracked.customizerAdding(BundleTracker.java:1)
at org.osgi.util.tracker.AbstractTracked.trackAdding(AbstractTracked.java:256)
at org.osgi.util.tracker.AbstractTracked.track(AbstractTracked.java:229)
at org.osgi.util.tracker.BundleTracker$Tracked.bundleChanged(BundleTracker.java:443)
at org.eclipse.osgi.framework.internal.core.BundleContextImpl.dispatchEvent(BundleContextImpl.java:847)
at org.eclipse.osgi.framework.eventmgr.EventManager.dispatchEvent(EventManager.java:230)
at org.eclipse.osgi.framework.eventmgr.ListenerQueue.dispatchEventSynchronous(ListenerQueue.java:148)
at org.eclipse.osgi.framework.internal.core.Framework.publishBundleEventPrivileged(Framework.java:1568)
at org.eclipse.osgi.framework.internal.core.Framework.publishBundleEvent(Framework.java:1504)
at org.eclipse.osgi.framework.internal.core.Framework.publishBundleEvent(Framework.java:1499)
at org.eclipse.osgi.framework.internal.core.BundleHost.startWorker(BundleHost.java:391)
at org.eclipse.osgi.framework.internal.core.AbstractBundle.start(AbstractBundle.java:300)
at org.eclipse.osgi.framework.internal.core.AbstractBundle.start(AbstractBundle.java:292)
at org.eclipse.virgo.web.war.deployer.WARDeployer.start(WARDeployer.java:780)
at org.eclipse.virgo.nano.deployer.internal.StandardApplicationDeployer.startDeployables(StandardApplicationDeployer.java:325)
at org.eclipse.virgo.nano.deployer.internal.StandardApplicationDeployer.bulkDeploy(StandardApplicationDeployer.java:116)
at org.eclipse.virgo.nano.deployer.hot.HotDeploymentFileSystemListener.bulkDeployIfNotDeployed(HotDeployerFileSystemListener.java:143)
at org.eclipse.virgo.nano.deployer.hot.HotDeploymentFileSystemListener.onInitialEvent(HotDeployerFileSystemListener.java:105)
at org.eclipse.virgo.util.io.FileSystemChecker.notifyListenersOnInitialEvent(FileSystemChecker.java:207)
at org.eclipse.virgo.util.io.FileSystemChecker.handleInitialFiles(FileSystemChecker.java:177)
at org.eclipse.virgo.util.io.FileSystemChecker.check(FileSystemChecker.java:261)
at org.eclipse.virgo.nano.deployer.hot.WatchTask.run(WatchTask.java:49)
at java.lang.Thread.run(Thread.java:807)

Followed by:

• One or more listeners failed to start. Full details will be found in the appropriate container log file
• Context [] startup failed due to previous errors

This will destroy my Servlet Context Listener and then failed to start web application in NEO.

It is strange because the method is called well and in the log I can see that the method is called without an error.

If I don't call the method in code, the application is starting up well.

Please let me know, how I can solve this issue, because I need to call the S/4 Hana system.

Answer 1

Update:

Version 2.0.0 of the SAP S/4HANA Cloud SDK changed the way how RequestContextListeners are initialized. It is now be possible to use the following code without additional effort:

new RequestContextExecutor().execute(...);

Original answer:

I guess that you want to run logic in some background task that is not triggered by a user request.

Can you try to wrap the logic calling the S/4HANA system in a Callable which is passed to the execute method of a RequestContextExecutor?

For example:

List<SomeData> result = new RequestContextExecutor()
    .execute(new Callable<List<SomeData>>() {
        @Override
        public List<SomeData> call() {
            return new GetSomeDataCommand().execute();
        }
    });

Note that this will require a technical user with Basic credentials in the destination configuration; principal propagation is not available in this case.

Also note that if you want to run the background task calling the external system in a ServletContextListener during application startup, you have to

• either explicitly register the relevant RequestContextListener classes which are also subclasses of ServletContextListener (including, if you are using the SAP Cloud Platform Neo environment, initializing the ScpNeoHystrixBootstrapListener),
• or specify the order of the ServletContextListener classes explicitly in the web.xml file.

You can register these listeners explictly as follows:

// ensure that the correct HystrixConcurrencyStrategy is used
new ScpNeoHystrixBootstrapListener().bootstrap();

// explicitly register RequestContextListeners
new RequestContextExecutor().withListeners(
    new DestinationsRequestContextListener(),
    new ScpNeoDestinationsRequestContextListener(),
    new TenantRequestContextListener(),
    new UserRequestContextListener()
).execute( /* callable */ );