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README.md
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README.md

This document contains documentation for the tracee-api module. Check the TracEE main documentation to get started.

tracee-api

This module contains the public api for users (applications) and service provider implementations.

Manipulating the context from your application code

TracEE is designed to keep your application and business code free from the aspect of propagation of contextual information. But it is still valid if your business code emits context information that you want to follow within further processing.

tracee-api contains a lightweight client api that allows you to attach parameters into the current invocation context. Use the TraceeBackend#put(String key, String value)-method to add a context parameter.

The key shares a namespace with all MDC entries, so make sure it is unique in your business code and does not conflict with other frameworks MDC entries. It might help to choose a common prefix for your applications context parameters.

The following example shows an EJB that uses a TraceeBackend to attach the context information of an orderNumber to the current system interaction.

@Stateless
public class MyBusinessService {

  private final TraceeBackend backend = Tracee.getBackend();

  @EJB
  OrderService orderService;

  public void makeBigBusiness(Customer customer, Item ... items) {
		final int orderNumber = orderService.getNextOrderNumber();
		backend.set("MyBusiness.orderNumber", orderNumber);
		try {
		  final Order order = orderService.create(customer);
		  order.addItems(items);
		  orderService.processOrder();
		} finally {
		  backend.remove("MyBusiness.orderNumber");
		}
  }

}

Be aware, that you really should remove your custom context parameters as soon as the become invalid.

Please keep in mind that parameters in the TracEE-Context are meant for logging. Do not use it as a hack to pass actual business parameters alongside your business method signatures.

TracEE backends

TracEE uses SLF4J as default logging backend. It uses the MDC to store the values and logs through SLF4J itself. - But most of the time TracEE is very silent.

If you have no logging backend present in a component, you can still use the threadlocal-store as backend that supports propagation of parameters (but leaves out the logging part).

Implementing custom backends to store the values

You can make your own backend by implementing the io.tracee.spi.TraceeBackendProvider interface and create a provider-configuration file classpath:/META-INF/services/io.tracee.spi.TraceeContextProvider (see JDKs ServiceLoader).

The module tracee-core contains abstractions over MDC-like logging backends that may help you with your integration.

(But add the SLF4J logging API in every case! TracEE uses the API to log errors or other states. TracEE feels comfortable with the NOPLogger of SLF4J.)