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Modules

In the para-server package, there are several core modules:

  • PersistenceModule - defines the core persistence class implementation
  • SearchModule - defines the core search class implementation
  • CacheModule - defines the core cache class implementation
  • EmailModule - defines an email service implementation for sending emails
  • QueueModule - defines a queue service implementation
  • StorageModule - defines a file storage service, e.g. Amazon S3

Para uses the ServiceLoader mechanism in Java to load other plugins and implementations.

For example, let’s say you want to implement a new PersistenceModule which connects to MySQL. You can define it like so:

package org.acme.para.dao.impl;


import com.erudika.para.core.persistence.DAO;


class MyDAO implements DAO {
  // TODO: implement all CRUD methods
}

Then implement the DAO interface in your class MyDAO.

You can then load the module programmatically like this:

DAO dao = new MyDAO();
ParaServer.initialize(dao, new CaffeineCache(), new LuceneSearch(dao), new LocalQueue(), new LocalFileStore());

Alternatively, you can use the ServiceLoader route and register a new DAO implementation.

  1. Create the file src/main/resources/META-INF/services/com.erudika.para.core.persistence.DAO. Put the full class name on one line inside that file:

    org.acme.para.dao.impl.MyDAO

  2. Configure Para to load the module:

    para-application.conf
    para.dao = "MyDAO"

Lifecycle events

Section titled “Lifecycle events”

To initialize and destroy Para programmatically with the default modules, call these methods:

// Initialize Para and call each listener.onInitialize()
ParaServer.initialize();


// Finally, destroy all resources by calling each listener.onDestroy()
ParaServer.destroy();

If you’re defining your own custom classes, don’t forget to set:

System.setProperty("para.core_package_name", "com.company.myapp.core");

There are two additional methods Para.initialize() and Para.destroy() which are now part of para-core. The difference between these and the ones above is:

// Invokes all registered InitializeListener
// instances and prints out logo to console;
Para.initialize()
// Loads all modules, and starts all registered
// InitializeListener objects, then calls Para.initialize()
ParaServer.initialize()
// Invokes all registered `DestroyListener` instances
// and prints out a log message
Para.destroy()
// injects concrete types into each `DestroyListener`
// and calls `Para.destroy()
ParaServer.destroy()