How can Apache Camel be used to monitor file changes?

Question

I would like to monitor all of the files in a given directory for changes, ie an updated timestamp. This use case seems natural for Camel using the file component, but I can't seem to find a way to configure this behavior. A uri like: ``` file:/some/directory ``` will consume the files in the provided directory but will delete them. A uri like: ``` file:/some/directory?noop=true ``` consumes each file once when it is added or when the route is started. It's surprising that there isn't an option along the lines of ``` consumeOnChange=true ``` Is there a straightforward way to monitor file changes and not delete the file after consuming?

Accepted Answer

You can do this by setting up the idempotentKey to tell Camel how a file is considered changed. For example if the file size changes, or its timestamp changes etc.

See more details at the Camel file documentation at: https://camel.apache.org/components/latest/file-component.html

See the section Avoiding reading the same file more than once (idempotent consumer). And read about idempotent and idempotentKey.

So something alike

```
from("file:/somedir?noop=true&idempotentKey=${file:name}-${file:size}")
```

Or

```
from("file:/somedir?noop=true&idempotentKey=${file:name}-${file:modified}")
```

You can read here about the various ${file:xxx} tokens you can use: http://camel.apache.org/file-language.html

How can Apache Camel be used to monitor file changes?

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