How to initialize injected value before REST call?

Question

I have a JAX-RS Application (running Jersey 2 on Tomcat) that relies on a heavyweight connection to HBase. I want to initialize and reuse that connection throughout my application for multiple resources. I have set up a Binder that binds the connection as a Singleton, and used the @Inject annotaton to inject that connection into my resource. However, since the injection doesn't occur until the first call of the service, the connection isn't initialized until then.

The application:

public class MyApplication extends ResourceConfig {

    public MyApplication() {
        super(MyResource.class);
        register(new HbaseBinder());
    }
}

The Binder:

public class HbaseBinder extends AbstractBinder {

    @Override
    protected void configure() {
        bindAsContract(HbaseConnection.class).in(Singleton.class);
        bind(new HbaseConnection()).to(HbaseConnection.class);
    }
}

The Injection:

@Path("/myResource")
public class MyResource {

    @Inject
    private HbaseConnection hbaseConnection;

    ...
}

The HBase Connection:

@Singleton
public class HbaseConnection {    
    public Connection getConnection() throws IOException {
        ...
    }
    ...
}

What I would like to do is initialize the Singleton at application deployment time so that it's ready to go on the first call to the service. What is the proper way to do this?

Answer 1

Thank you for all of the comments and answers. A combination of the above were required.

Part of the issue was that I was using the the @PostConstruct to call the HbaseConnection.getConnection() method had an unchecked exception. Once I got rid of that, and switch to the Immediate scope, the class seems to be loaded appropriately. Here's my final solution:

public class MyApplication extends ResourceConfig {

    @Inject
    public MyApplication(ServiceLocator locator) {
        super(MyResource.class);
        register(new HbaseBinder());
        ServiceLocatorUtilities.enableImmediateScope(locator);
    }
}

---

@Path("/myResource")
public class MyResource {    

    @Inject
    private HbaseConnection hbaseConnection;

    ...
}

---

public class HbaseBinder extends AbstractBinder {

    @Override
    protected void configure() {
        bindAsContract(HbaseConnection.class).in(Immediate.class);
    }
}

---

@Immediate
public class HbaseConnection {

    @PostConstruct
    public void postConstruct() {
        // Call getConnection(), wrapped in try/catch.
    }

    public Connection getConnection() throws IOException {
        // Get the connection.
    }

    @PreDestroy
    public void preDestroy() {
        // Call cleanup(), wrapped in try/catch.
    }

    public void cleanup() throws IOException {
        // Close/cleanup the connection
    }
}

Now my only problem is that it looks like some Threads/ThreadLocals are being left around on undeployment, but this has to be bugs in the libraries that I'm using as I have no control over their lifecycle.

12-Feb-2016 14:01:45.054 INFO [ContainerBackgroundProcessor[StandardEngine[Catalina]]] org.apache.catalina.startup.HostConfig.undeploy Undeploying context [/my-resource]
12-Feb-2016 14:01:46.129 WARNING [ContainerBackgroundProcessor[StandardEngine[Catalina]]] org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesThreads The web application [my-resource] appears to have started a thread named [ImmediateThread-1455303641406] but has failed to stop it. This is very likely to create a memory leak. Stack trace of thread:
 sun.misc.Unsafe.park(Native Method)
 java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:215)
 java.util.concurrent.SynchronousQueue$TransferQueue.awaitFulfill(SynchronousQueue.java:764)
 java.util.concurrent.SynchronousQueue$TransferQueue.transfer(SynchronousQueue.java:695)
 java.util.concurrent.SynchronousQueue.poll(SynchronousQueue.java:941)
 java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1066)
 java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1127)
 java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
 java.lang.Thread.run(Thread.java:745)
12-Feb-2016 14:01:46.130 WARNING [ContainerBackgroundProcessor[StandardEngine[Catalina]]] org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesThreads The web application [my-resource] appears to have started a thread named [Thread-5] but has failed to stop it. This is very likely to create a memory leak. Stack trace of thread:
 sun.net.dns.ResolverConfigurationImpl.notifyAddrChange0(Native Method)
 sun.net.dns.ResolverConfigurationImpl$AddressChangeListener.run(ResolverConfigurationImpl.java:144)
12-Feb-2016 14:01:46.134 SEVERE [ContainerBackgroundProcessor[StandardEngine[Catalina]]] org.apache.catalina.loader.WebappClassLoaderBase.checkThreadLocalMapForLeaks The web application [my-resource] created a ThreadLocal with key of type [org.apache.htrace.core.Tracer.ThreadLocalContext] (value [org.apache.htrace.core.Tracer$ThreadLocalContext@2c25bbe0]) and a value of type [org.apache.htrace.core.Tracer.ThreadContext] (value [org.apache.htrace.core.Tracer$ThreadContext@787153ae]) but failed to remove it when the web application was stopped. Threads are going to be renewed over time to try and avoid a probable memory leak.
12-Feb-2016 14:01:46.135 SEVERE [ContainerBackgroundProcessor[StandardEngine[Catalina]]] org.apache.catalina.loader.WebappClassLoaderBase.checkThreadLocalMapForLeaks The web application [my-resource] created a ThreadLocal with key of type [org.apache.hadoop.io.Text$1] (value [org.apache.hadoop.io.Text$1@1badb836]) and a value of type [sun.nio.cs.UTF_8.Encoder] (value [sun.nio.cs.UTF_8$Encoder@13652d32]) but failed to remove it when the web application was stopped. Threads are going to be renewed over time to try and avoid a probable memory leak.
12-Feb-2016 14:01:46.136 SEVERE [ContainerBackgroundProcessor[StandardEngine[Catalina]]] org.apache.catalina.loader.WebappClassLoaderBase.checkThreadLocalMapForLeaks The web application [my-resource] created a ThreadLocal with key of type [org.apache.hadoop.hdfs.DFSUtil$1] (value [org.apache.hadoop.hdfs.DFSUtil$1@6080a3db]) and a value of type [java.util.Random] (value [java.util.Random@169acbf5]) but failed to remove it when the web application was stopped. Threads are going to be renewed over time to try and avoid a probable memory leak.
12-Feb-2016 14:03:02.383 INFO [Thread-7] org.apache.catalina.loader.WebappClassLoaderBase.checkStateForResourceLoading Illegal access: this web application instance has been stopped already. Could not load [org.apache.hadoop.util.ShutdownHookManager$2]. The following stack trace is thrown for debugging purposes as well as to attempt to terminate the thread which caused the illegal access.
 java.lang.IllegalStateException: Illegal access: this web application instance has been stopped already. Could not load [org.apache.hadoop.util.ShutdownHookManager$2]. The following stack trace is thrown for debugging purposes as well as to attempt to terminate the thread which caused the illegal access.
    at org.apache.catalina.loader.WebappClassLoaderBase.checkStateForResourceLoading(WebappClassLoaderBase.java:1353)
    at org.apache.catalina.loader.WebappClassLoaderBase.checkStateForClassLoading(WebappClassLoaderBase.java:1341)
    at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1206)
    at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1167)
    at org.apache.hadoop.util.ShutdownHookManager.getShutdownHooksInOrder(ShutdownHookManager.java:124)
    at org.apache.hadoop.util.ShutdownHookManager$1.run(ShutdownHookManager.java:52)

12-Feb-2016 14:03:02.383 INFO [Thread-4] org.apache.coyote.AbstractProtocol.pause Pausing ProtocolHandler ["http-apr-8080"]
12-Feb-2016 14:03:02.449 INFO [Thread-4] org.apache.coyote.AbstractProtocol.pause Pausing ProtocolHandler ["ajp-apr-8009"]
12-Feb-2016 14:03:02.500 INFO [Thread-4] org.apache.catalina.core.StandardService.stopInternal Stopping service Catalina
12-Feb-2016 14:03:02.530 INFO [Thread-4] org.apache.coyote.AbstractProtocol.stop Stopping ProtocolHandler ["http-apr-8080"]
12-Feb-2016 14:03:02.581 INFO [Thread-4] org.apache.coyote.AbstractProtocol.stop Stopping ProtocolHandler ["ajp-apr-8009"]

Answer 2

Your HbaseConnection gets initialized twice.

• at first, it initializes in your binder (provided your MyApplication class is registered as init-param in your web.xml)
• and then, it initializes once again when HK2 detects @Singleton annotation (or when it proceeds the bindAsContract instruction)

As a result, to make your example work, you need to:

1. remove @Singleton annotation from your HbaseConnection class.
2. remove line bindAsContract(HbaseConnection.class).in(Singleton.class); from your HBaseBinder class

The initialization of MyApplication happens during the servlet container startup (thus the construction of HbaseConnection) which is what you want, right?

It's you, who's providing the instance (in the binder), not HK2. That's why you don't want to instruct it by using @Singleton to create the instance.

The binder should be:

public class HbaseBinder extends AbstractBinder {

    @Override
    protected void configure() {
        // just bind is ok
        bind(new HbaseConnection()).to(HbaseConnection.class);
    }
}

And the HBase Connection:

// do not annotate with `@Singleton`!
public class HbaseConnection {    
    public Connection getConnection() throws IOException {
        ...
    }
    ...
}