[← IDE metadata](07-ide-metadata.md) · [Index](../README.md)

# 8. Diagnosing a value

Endpoint: [`BindingDiagnosticsEndpoint`](../src/main/java/com/ankurm/configprops/web/BindingDiagnosticsEndpoint.java).

"The property is set but the application does not see it" is the most common configuration bug,
and it is hard for one reason: a value carries no visible provenance. Spring Boot tracks it
anyway — every property loaded from a file or a config tree carries an `Origin` naming the
resource and the line.

```
$ curl -s 'localhost:8080/diag/origin?name=demo.mail.host'
{
  "property": "demo.mail.host",
  "effectiveValue": "smtp.example.com",
  "candidatesInPrecedenceOrder": [
    {
      "source": "OriginTrackedMapPropertySource {name='Config resource ... [application.yaml]'}",
      "value": "smtp.example.com",
      "origin": "class path resource [application.yaml] - 15:11"
    }
  ]
}
```

Line 15, column 11. Not "somewhere in your configuration".

## How it works

```java
for (ConfigurationPropertySource source : ConfigurationPropertySources.get(environment)) {
    ConfigurationProperty property =
            source.getConfigurationProperty(ConfigurationPropertyName.of(name));
    if (property != null) {
        // property.getValue(), property.getOrigin(), source.getUnderlyingSource()
    }
}
```

Iterating `ConfigurationPropertySources.get(...)` gives you the sources in precedence order.
The first hit is the winner; everything after it exists and lost. A property with several
holders is exactly what "my change had no effect" looks like from the inside — and the
[profiles project](../../profiles-and-config) is entirely about that case.

## Delete it before shipping

This endpoint prints whatever a mounted secret contains. If you want it permanently, put it
behind the management port and authentication, or use Actuator's `/actuator/env`, which does
the same job with sanitisation built in.

## Without an endpoint

- `--debug` prints the auto-configuration report, not property origins.
- Setting `logging.level.org.springframework.boot.context.config=TRACE` logs which config data
  resources were loaded, in order — useful when the question is "was my file read at all".
- In a test, inject `Environment` and inspect `getPropertySources()` directly.