concept Spring scheduler in category spring
This is an excerpt from Manning's book Spring Batch in Action.
Is cron suited to launch your Spring Batch job? Remember, cron is a system scheduler: it spawns a new JVM process for each Spring Batch command-line launcher. Imagine that you need to launch a job every night. Cron triggers the command-line launcher, which creates a Spring application context before launching the job itself. Everything is fine. But imagine now that you need to launch another job that scans a directory for new files to import. You set up cron to trigger this job every minute. If bootstrapping the Spring application context is CPU intensive—because it initializes a Hibernate SessionFactory or a Java Persistence API context, for example—the job execution will perhaps be faster than the creation of the Spring application context! In this second case, you prefer to have your Spring application context already running and then simply launch the job from the existing JobLauncher. You can’t easily achieve this from the command line (hence with cron), but a Java scheduler like the Spring scheduler will do the trick.
Figure 4.8. A web application can contain a Spring application context. This Spring application context can host Spring Batch’s infrastructure (job launcher, job repository) and jobs. The context can also host a Java-based scheduler (like Spring scheduler or Quartz) and any Spring beans related to the web application (data access objects, business services).
Spring’s lightweight scheduling provides features like cron expressions, customization of threading policy, and declarative configuration with XML or annotations. For XML configuration, Spring provides the task XML vocabulary (under the namespace www.springframework.org/schema/task), which comes in handy to configure and schedule tasks. The Spring scheduler needs a running Spring application context to work, so you typically embed it in a web application, but you can use any other managed environment, like an Open Services Gateway initiative (OSGi) container. We cover how to embed Spring Batch in a web application in section 4.4.1.