Apache Camel is all about integration, and has built-in support for most of the things you need. One integration pattern you might need is to process files in a directory, and send the contents over HTTP to a web service endpoint. You can do this using Camel’s File and HTTP components.
Suppose you want to send JSON files to a web service using HTTP POST. This is straightforward: the Camel File component consumes the file, creating a Camel message, and the HTTP component will send the message body (the JSON data) to the specified URL in the body on an HTTP POST request. If the web service is expecting a request body with a different encoding, though, you’ll have to do a little more work.
Sending file contents using HTML form file upload
Suppose you have a legacy web service that is designed to handle file uploads from an HTML form. For example, it might use a form like this, which uploads a file and uses an additional form field for a file name:
To send binary file data in the request, the form must use the multipart/form-data encoding. This encoding handles multiple form parameters, each of which can be text or encoded binary. To use the same API from Camel, you have to apply the same form encoding.
Applying multipart form data encoding in Camel
The Camel HTTP component doesn’t do any request body encoding, and just sends the current message as-is. To send the same request as the HTML form, so the legacy web service can handle it, you have to encode the file contents.
To do a transformation in a Camel route, you need a function with a single
Exchange parameter that you can pass to the Scala DSL’s
The Apache HttpComponents library handles multipart MIME encoding, via the MultipartEntityBuilder API, so you can use that to encode the file. The resulting Camel processor implementation is as follows.
Note that the call to
exchange.getIn.getBody uses a built-in type conversion to
java.io.File, which you can pass to the
MultipartEntityBuilder to add a binary section.
Sending the file upload from a Camel route
Now you have the
toMultipart processor, you can use it in a Camel route that takes files from an
incoming directory, and sends them to
localhost:9000/upload. The following example uses the Scala DSL to do this.
Note that when you’re using web services, it’s a good idea to log HTTP requests and responses, especially HTTP error responses. Once you’re in production, you’ll be glad you did.