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# 5. `spring.config.import`

Transcript: [`04-import-and-multidoc.txt`](output/04-import-and-multidoc.txt).

```yaml
spring:
  config:
    import: "optional:classpath:/imported.yaml"
```

## The imported file wins

This is the part that catches people, and it catches them in the direction opposite to the one
they brace for:

```
  effective value : from-imported-yaml
    1. from-imported-yaml            <- imported.yaml
    2. from-application-import-yaml  <- application-import.yaml   (declared the import)
    3. from-application-yaml         <- application.yaml
```

The importing file declared the import and then lost to it. An imported document is processed
*after* the document that declared it, and later documents win.

`#include` semantics would give the opposite. So would treating the import as a set of
defaults, which is what people usually intend when they import a shared baseline. If you import
a company-wide `common.yaml` expecting your own file to override it, every key `common.yaml`
sets will quietly beat yours.

To get defaults-style behaviour, put your overrides somewhere that outranks config data — an
environment variable or a command-line argument — or import from a *later* document in your own
file so the ordering is explicit.

## Prefixes

| Prefix | Meaning |
|---|---|
| `optional:` | do not fail if it is missing |
| `file:` | a filesystem path |
| `classpath:` | a classpath resource |
| `configtree:` | a directory of value-per-file entries |

They compose: `optional:configtree:/etc/config/`.

Without `optional:`, a missing location is `ConfigDataLocationNotFoundException` at startup.
That is usually what you want for a secret mount and never what you want for a developer
machine.

## Where imports are legal

`spring.config.import` is only honoured in config data — `application.yaml` and friends. Setting
it as an environment variable or a command-line argument works too, because those are processed
before config data is loaded. Setting it anywhere else does nothing.

Imports are processed depth-first, and a cycle is detected and reported rather than looping.