$ lein run -m systems.simple-system2/mainLiking cljdoc? Tell your friends :D
Simple workflow
In this example we’re going to create a really simple system with a simple
linear workflow. The workflow is really simple, data will flow from component-1
to component-2 and then component-3. Each component transoform the value and put
it to the output.
In order to execute the following example from the hellhound_examples repository. Just issue the following command in the repository root directory.
Ok let’s jump into the code.
link:simple_system2.clj[role=include]| 1 | The start function of the component 1 which will assign
to the component later in the component map.
The first argument is the componet map itself and the argument
is the context map which contains extra info about the context
which this component is running on.
As you already know start function of a component should return
a component map.
This component basically applies function inc on any incoming
value from its input and put it to its output. |
| 2 | Gets the input of the current component |
| 3 | Gets the output of the current component |
| 4 | Connects input to output via an anonymous function which
applies inc function to incoming values and dispatches them
to the output |
| 5 | Simply consumes any incoming value and applies a function to that value |
| 6 | Defining all three components needed for this system to work. Please notice that we didn’t defined any dependencies for these components. Pluging them to each other using a workflow catalog is a different story from component dependencies. We only need to define a component as a dependency if the second component use the first one directly in its start or stop function. |
| 7 | Defines a system with a linear workflow. In this case HellHound starts all
the components in the system and then wires up components IO based on the
desciption given by the :workflow key of the system. |
| 8 | Gets a component with the name from the default system. |
| 9 | Converts the vector to a stream source |
| 10 | Connects the stream source to the input of component1 |
|
In the system of this example, the workflow is like: DATA ---> component-1 ---> component-2 ---> component-3 Component 3 don’t have any output stream. But it can have one. |
When we execute the above code the output would be something like:
The output of the above namespace
[17-10-29 21:52:37] [DEBUG] <hellhound.component:115> - Starting component ':simple-system/component-2'...
[17-10-29 21:52:37] [DEBUG] <hellhound.component:115> - Starting component ':simple-system/component-1'...
[17-10-29 21:52:37] [DEBUG] <hellhound.component:115> - Starting component ':simple-system/component-3'...
[17-10-29 21:52:37] [INFO] <hellhound.system.core:142> - System started successfully.
[17-10-29 21:52:37] [DEBUG] <hellhound.system.workflow:107> - Setting up workflow...
[17-10-29 21:52:37] [INFO] <hellhound.system.workflow:110> - Workflow setup done.
Message Component 1: 1
Message Component 2: 2
Message Component 3: 3
Message Component 1: 2
Message Component 2: 3
Message Component 3: 4
Message Component 1: 3
Message Component 2: 4
Message Component 3: 5
Message Component 1: 4
Message Component 2: 5
Message Component 3: 6
Message Component 1: 5
Message Component 2: 6
Message Component 3: 7
Message Component 1: 6
Message Component 2: 7
Message Component 3: 8
Done.As you can see the output above data flows to the pipeline and each component transoforms the value it gets from its input to a new value and put it into the output.
In the above example we used a simple vector and converted it to a stream source, but in practice the data flows to our system from an external source like a web server.
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