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# README - slf4j-reference
This project gives an example of ONAP-compliant logging using SLF4J logging.
## Adapter
In ```org.onap.logging.ref.slf4j```, there are TWO classes:
1. ```org.onap.logging.ref.slf4j.ONAPLogConstants```, providing declarations of standard ONAP Markers, MDCs and HTTP headers.
2. ```org.onap.logging.ref.slf4j.ONAPLogAdapter```, providing a lightweight, compliant implementation of the ONAP logging spec.
The adapter provides:
1. A loosely-coupled SLF4j logging wrapper:
* To be used for logging ONAP ```entry```, ```exit``` and ```invoke``` behavior.
* Devolving all *application* logging to the component, via the regular SLF4J ```Logger``` facade.
2. Customization options:
* *Cheap*, by way of bean properties. This is suited to most Use Cases.
* *Sophisticated*:
* By OPTIONALLY implementing one of a number of adapters:
* ```RequestAdapter``` to read incoming headers.
* ```ServiceDescriptor``` for reporting attributes of the current service.
* ```ResponseDescriptor``` for reporting outcomes.
* ```RequestBuilder``` for setting southbound request headers.
* By OPTIONALLY overriding methods like ```ONAPLogAdapter#setMDCs(RequestAdapter)```.
Note that:
* The adapter implementation uses static inner classes in order to fit in a single source file. This was an objective.
## WAR
Building produces a simple (spring-boot](https://projects.spring.io/spring-boot/) example WAR, which can be launched from this directory with:
```bash
$ java -war target/*war
```
The example WAR in ```logging-slf4j-demo``` publishes four web services:
1. ```services/alpha```
2. ```services/beta```
3. ```services/gamma```
4. ```services/delta```
... each of which can invoke the others.
The purpose of the WAR is to demonstrate minimalist ONAP-compliant logging for web components, but a secondary purpose is to demonstrate that the call graph can be generated for a (mostly) representative set of interacting REST services.
## Tests
Tests for:
1. Code in the (potentially) reusable ``common`` package.
2. Validating that emitted logs can be used to generate an unambiguous call graph.
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