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.
Related
I was reviewing a code which seems to lose connection to DB approximately once a month intermittently. It leaves no logs on DB side but server prints a log of Connection closed by peer.
Its a Spring Boot App (2.1.9) which uses Spring Integration to read from queues (JMS).
Under pom.xml spring-boot-started-jdbc , Hikari is excluded and tomcat is used.
The app is designed in such a way that it has an in-queue to get traffic, then series of internal queues to split the workload and finally an out queue to the destination.
This app has 4 datasources created all pointing to the same oracle database.
First datasource is used for all CRUD operations in the flow between in-queue and first internal queue. Second datasource is used for all CRUD operations in the flow between first and second internal queue. Third datasource is used between second internal queue and destination queue. Fourth datasource is not used anywhere which suggests some flow was commented but datasource was never removed.
Each datasource has different min and max connections but rest of the properties are same.
Wanted to understand is that a good practice to create
datasources for each spring integration flow pointing to same database?
Can it cause any problems to leave a datasource initialized without using it anywhere?
Is there any obvious reason why HikariCP shouldn't be chosen for production when lot of matrix online show Hikari is superior to Tomcat and Spring boot 2 has chosen it as default for a reason?
I am storing application.properties file in my config server. And my client applications are refering config server to download the property files.
Scenario 1:
When i change the value of property server.port in my config server. Can i reflect the changes in my client applicaiton without restarting the application.
You can use #RefreshScope beans for this purpose, this is not ideal but as close as you can get in config server, this is a pretty advanced thing after all.
So beans marked with this annotations will cause spring to clear the internal cache of the beans / configuration classes upon EnvironmentChangeEvent, then the instance of the bean will be created next time you'll try to call this bean.
To trigger such an event when the config server changes you can either explicitly call the actuator's refresh enpoint or develop your own solution that might be based on some messaging system so that the config server will be a producer of a "change" message and the consumer will be your application.
Now I can't say for sure whether it will work in particular with server.port, I've personally never seen a need to change this property, but for your custom beans this method will do the job.
Here is a good tutorial about this topic
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.
I have been researching Spring Data Rest especially for cassandra and one of the questions my coworkers and I had was when does Spring Data connect to the database. We don't always want a rest controller to connect to the database so when does spring establish a connection if say we had a class extend the CRUDRepository? Does it connect to the database during the start of application itself? Is that something we can control?
For example, I implemented this example on Spring's website:
https://spring.io/guides/gs/accessing-data-rest/
At what point in the code does spring connect to the database?
Spring will connect to the DB as soon as the Datasource get initialized. Basically, Spring contexts will become alive somehow (Web listeners, manually calling them) and start creating beans. As soon as it reaches the Datasource, connection will be made and the connection pool will be populated.
Of course the above is based on a normal out of the box configuration and everything can be setup up to your taste.
So unless, you decide to control the connections yourself, DB connections will be sitting there waiting to be used.
Disagree with the above answer.
As part of research i initiated the datasource using a bean configuration and then changed my database password(not in my spring application but the real db username password)
The connection stays for a while and then in some point of time (maybe idle time) it stops working and throws credential exception.
This is enough to say the JPA does not keep the connection sitting and waiting to be used but uses some mechanism to occupy/release the db connection as per the need.
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)