Writing Integrations in YAML

The YAML DSL is current in preview support level.

Defining a route

A route is a sequence of elements, or steps, defined as follow:

from: (1)
  uri: "direct:start"
  steps: (2)
    - filter:
        expression:
          simple: "${in.header.continue} == true"
        steps: (2)
          - to:
              uri: "log:filtered"
    - to:
        uri: "log:original"

1	route entry point, by default `from` and `rest` are supported
2	processing steps

Each step is represented by YAML map that has a single entry where the field name is the EIP name

As general rule each step provide all the parameters the related definition declares but there are some minor differences/enhancements:

Output Aware Steps

Some steps such as filter and split have their own pipeline when an exchange matches the filter expression or for the items generated by the split expression, such pipeline can be defined by the steps field:
```
filter:
  expression:
    simple: "${in.header.continue} == true"
      steps:
        - to:
            uri: "log:filtered"
```
if the steps field is omitted, then each subsequent step is considered part of the filter pipeline.
Expression Aware Steps

Some EIP such as filter and split supports the definition of an expression through the expression field:
Explicit Expression field
```
filter:
    expression:
      simple: "${in.header.continue} == true"
```
To make the DSL less verbose, the expression field can be omitted:
Implicit Expression field
```
filter:
    simple: "${in.header.continue} == true"
```
In general expression can be defined inline like in the examples above but in case you need provide more information, you can 'unroll' the expression definition and configure any single parameter the expression defines.
Full Expression definition
```
filter:
    tokenize:
      token: "<"
      end-token: ">"
```
Data Format Aware Steps

Some EIP such as set-body and marshal supports the definition of data formats through the data-format field:
Explicit Data Format field
```
set-body:
    data-format:
      json:
        library: Gson
```
To make the DSL less verbose, the data-format field can be omitted:
Implicit Data Format field
```
set-body:
    json:
      library: Gson
```
In case you want to use the data-format’s default settings, you need to place an empty block as data format parameters, like json: {}

Extending the DSL

The DSL is designed to be easily extended so you can provide your own step handler which is discovered at runtime using Camel’s factory finder.

Assuming you want to create a step to simplify the creation of a certain type of endpoints then you need:

create a service definition entry in META-INF/services/org/apache/camel/k/yaml with content like:
```
class=com.acme.converter.MyConverter
```

create the step handler extending org.apache.camel.k.loader.yaml.parser.ProcessorStepParser

package com.acme.converter.AcmeConverter

import org.apache.camel.k.loader.yaml.parser.ProcessorStepParser;

public class AcmeConverter
        implements ProcessorStepParser {
    /**
     * @param context contains a references to the camel context and the current node as raw JsonNode
     */
    @Override
    public ProcessorDefinition<?> toProcessor(Context context) {
        // decode the raw json node
        Definition definition = context.node(Definition.class);

        // create the definition
        ToDefinition to = new ToDefinition()
        to.setUri(String.format("http://%s:%d/fixed/path"), definition.host, definition.port)

        return to;
    }

    /*
     * Define the data
     */
    public static final class Definition {
        public String host;

        @JsonSetter(nulls = Nulls.SKIP)
        public Integer port = 8080;
    }
}

Assuming the entry in the META-INF/services/org/apache/camel/k/yaml is named acme then you can use it from the YAML DSL like:

from:
  uri: "direct:start"
  steps:
    - acme:
        host: acme.com
        port: 8081

Supported EIP

Aggregate
Bean
Choice
Circuit Breaker
Claim Check
Convert Body To
Delay
Dynamic Router
Enrich
Filter
From
Idempotent Consumer
Load Balance
Log
Loop
Marshal
Multicast
Pipeline
PollEnrich
Process
Recipient List
Remove Header
Remove Headers
Remove Property
Remove Properties
Resequence
Rest DSL
Rollback
Routing Slip
Saga
Sample
Script
ServiceCall
Set Body
Set Exchange Pattern
Set Header
Set Property
Sort
Split
Step
Stop
Threads
Throttle
Throw Exception
To
To Dynamic
Transacted
Transform
Try Catch Finally
Unmarshal
Validate
Wire Tap

The Try Catch Finally EIP currently only support specifying one do-catch clause.