I have a Spring servlet called with load-on-startup = 1 and it requires a database connection, but sometimes, connection is null and the appLoader servlet fails. The connection is null because tomcat didn't had the time to load the global resources properly.
Question : How do I ask Spring to wait for jndi proper loading? I mean, order it in some way.
Dirty solution : Make another servlet with active wait and waiting for a working connection before calling my appLoader...
1) The job of <load-on-startup> is to start a servlet at the time of deployment. It just initiates(starts) the process after that it has no control over that servlet.
The entire control of the started servlet is in the hands of the web container.
The behaviour of the web container can be programmatically controlled using Event Handling mechanism.
2) Events are basically occurrence of something. Changing the state of an object is known as an event.
2.1) You can handle the events of web container using event listeners of servlet and perform some important tasks such as creating tables of the database, creating database connection object etc. at time of deploying the project.
There are many Event classes and Listener interfaces in the javax.servlet and javax.servlet.http package.
You can use ServletContextListener to store the connection object in the context attribute and later fetch that connection object from servlet context.
Here are few examples where database connection object is stored in servlet context. example1 example2 example3
2.2) You can use Event Handling mechanism of spring framework.
In spring you can poll your database connection using ContextStartedEvent that is raised when an ApplicationContext gets started.
Here, are some spring events with example.
Related
In my Spring Application, at the time of context Initialization. The DB is not available, it will come up after some time (Due to DB redundancy). In this scenario, my spring application initialization should be delayed or the application should do retry for DB connectivity. How to achieve the same via Spring.
Srirama.
I'd suggest investigating the ApplicationContextInitializer. It is meant to be used for setting up your context before most of the magic of spring initialization happens.
I'm not sure if it is designed for your use case, but no beans are initialized when the initialize method is called during startup.
The example provided in the link deals with properties, but I see no reason why you should not create your own manually created connection and wait for it's readiness.
Thanks for the reply.
My application is initialized by means of C3P0. Here C3P0, is trying to reconnect to DB only for 30 times (the default configuration for acquireRetryAttempts) and after that it is saying failed to create the application beans.
Changed the configuration for acquireRetryAttempts to -1, so that C3P0 is retrying indefinitely till the DB connection is successful. Basically my app. initialization should be delayed till the DB comes up.
Srirama.
If I expose DataSource as a service in OSGI, how should I handle database connection failure? Should I configure an interceptor of the DataSource service, which would catch database connection failure exception and unregister the DataSource service? Or would OSGI container handle the exception for me?
How should I configure the consuming service, so that it would be able to survive unavailability of the DataSource service, and allow user to re-try the transaction again?
You should handle unexpected exceptions in the same way as you do when you do not use OSGi.
You should use connection-pool and register that as an OSGi service. It will handle connection failures for you. You must always close the connection, even if there is an exception during using that connection. (in finally block before java 6 and by using a try-with-resources block after java 7). Connection pools provide their functionality by implementing DataSource interface.
There are many connection-pools. You can google for them.
I implemented two OSGi components based on commons-dbcp. One for pooling regular DataSources and one for pooling XADataSources. The component picks up the original DataSource/XADataSource OSGi service, than registers a new pooled-DataSource OSGi service.
You can find the source of the module here: https://github.com/everit-org/commons-dbcp-component
It is available at maven-central here: http://search.maven.org/#artifactdetails%7Corg.everit.osgi%7Corg.everit.osgi.jdbc.commons.dbcp%7C2.0.1%7Cbundle
After dropping the jar into your OSGi container, you will see the configuration possibilities of the components at the Configuration page of WebConsole (if you have webconsole).
Need to call a EJB service from the servlet context listener's contextInitialized() method. Application is running on JBOSS, though the context listener works fine, I'm not able to access the EJB bean through JNDI look up.
Because the web deployment in JBOSS happens before EJB beans are bound with JNDI tree. How to overcome from this? Is there a way to configure JNDI bind early or start the web deployment later once EJB's are completely deployed?
I had put Thread.sleep() before the service call in the contextInitialized() method, it is working fine in my JBoss5.1.0 GA, and the same did not work in other machines JBoss of same version.
Applications needs this because, we want to load some master data from the DB and make it available in the web layer (kind of caching). Does JBOSS startupmbean suit this requirement? If yes how can I make the data available to web layer?
Also if any alternative ways are available, please suggest.
Poll for the EJBs in contextInitialized(). So instead of just sleeping for a certain time, try to connect to the EJB. If that fails, sleep, and retry, until the EJBs are available. In this case the context initialization is blocked.
Implement the cache as a lazy one: Fill the cache during the first query (and use the same polling procedure: connect to the EJB, retry until it becomes available). In this case the cache blocks.
You could split your deployment into two parts: One for the EJBs, one for the web application. Then deploy the first, and delay deployment of the web application until the EJBs are bound (either by watching the log file or by trying bind to the EJB from a command line app)
i saw some code use ShutdownHook like this
Runtime.getRuntime().addShutdownHook(new Thread(){
ConfigurableApplicationContext.stop();
//close spring context;
threadpool.shutdownnow();
//close theadpool
});
is there anything useful to do like this?
i thought
when jvm exit ,maybe thread will be shutdown immediately
and spring context will close tooï¼›
what shall we do next when we need to call System.exit() ?
It really depends on your application and the lifecycle of your objects and those threads you appear to have outside of your context. If you are running the spring container inside a standalone java process, then trapping the shutdown hook like this is one way to do that. Another way is to have it listen on a tcp port and send a command to begin the shutdown process. If you are running in a web container like tomcat, then you should follow the standards on normal webapp shutdown, which Spring supports with Context Listeners.
I would also consider redesigning your app so that the threads are all managed with a bean that lives inside your spring container. For instance using a bean that is configured with directives (attributes) for start/stop methods and then that bean would use an Executor for thread pooling. This way, your shutdown is ONLY shutting down the Spring container, and Spring provides very good support for orderly shutdown of beans. One of those beans is your object holding the threads within the Executor. Its a much cleaner way than trying to integrate Spring beans with external threads.
Hope this helps.
I am using spring portlet mvc as my front end and connecting to some remote EJB running on a WAS. Now in my configuration file for the portlet where I specify the remote EJB lookup url, I have specified the url(s) as a cluster since the EJB is deployed in a clustered WAS. So the url looks like :iiop://server1:port,iiop://server2:port.
Now to save resources, spring mvc caches the initial context.Now I am noticing that spring is always able to make a connection to the remote ejb so long as one of the servers is up.
This is confusing to me since the cluster is resolved(for lack of a better word) at the time of lookup of the initial context and after that if the cluster member goes down, there should be a connection exception. So how does spring know when it should automatically refresh its initial context because the old context has become stale?
I found that in the applicationContext.xml file, there is the declaration:
<jee:remote-slsb id="remoteService" jndi-name="com.business.ejb.ServiceSLRemote" business-interface="com.business.ejb.ServiceSLRemote" cache-home="true" lookup-home-on-startup="false" resource-ref="false" refresh-home-on-connect-failure="true">
<jee:environment>
java.naming.factory.initial=${JAVA.NAMING.FACTORY.INITIAL}
java.naming.provider.url=${JAVA.NAMING.PROVIDER.URL}
</jee:environment>
</jee:remote-slsb>
It is the refresh-home-on-connect-failure="true" that tells the spring container that if the initial context has become stale, then it should refresh the connection. That is how it can work so long as one cluster member is active.