115 lines
3.7 KiB
Markdown
115 lines
3.7 KiB
Markdown
---
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layout: pattern
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title: Pipeline
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folder: pipeline
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permalink: /patterns/pipeline/
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categories: Behavioral
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tags:
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- Decoupling
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---
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## Intent
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Allows processing of data in a series of stages by giving in an initial input and passing the processed output to be
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used by the next stages.
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## Explanation
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The Pipeline pattern uses ordered stages to process a sequence of input values. Each implemented task is represented by
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a stage of the pipeline. You can think of pipelines as similar to assembly lines in a factory, where each item in the
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assembly line is constructed in stages. The partially assembled item is passed from one assembly stage to another. The
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outputs of the assembly line occur in the same order as that of the inputs.
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Real world example
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> Suppose we wanted to pass through a string to a series of filtering stages and convert it as a char array on the last stage.
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In plain words
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> Pipeline pattern is an assembly line where partial results are passed from one stage to another.
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Wikipedia says
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> In software engineering, a pipeline consists of a chain of processing elements (processes, threads, coroutines, functions, etc.), arranged so that the output of each element is the input of the next; the name is by analogy to a physical pipeline.
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**Programmatic Example**
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The stages of our pipeline are called `Handler`s.
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```java
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interface Handler<I, O> {
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O process(I input);
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}
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```
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In our string processing example we have 3 different concrete `Handler`s.
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```java
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class RemoveAlphabetsHandler implements Handler<String, String> {
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...
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}
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class RemoveDigitsHandler implements Handler<String, String> {
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...
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}
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class ConvertToCharArrayHandler implements Handler<String, char[]> {
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...
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}
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```
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Here is the `Pipeline` that will gather and execute the handlers one by one.
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```java
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class Pipeline<I, O> {
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private final Handler<I, O> currentHandler;
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Pipeline(Handler<I, O> currentHandler) {
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this.currentHandler = currentHandler;
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}
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<K> Pipeline<I, K> addHandler(Handler<O, K> newHandler) {
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return new Pipeline<>(input -> newHandler.process(currentHandler.process(input)));
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}
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O execute(I input) {
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return currentHandler.process(input);
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}
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}
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```
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And here's the `Pipeline` in action processing the string.
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```java
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var filters = new Pipeline<>(new RemoveAlphabetsHandler())
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.addHandler(new RemoveDigitsHandler())
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.addHandler(new ConvertToCharArrayHandler());
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filters.execute("GoYankees123!");
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```
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## Class diagram
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## Applicability
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Use the Pipeline pattern when you want to
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* Execute individual stages that yields a final value
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* Add readability to complex sequence of operations by providing a fluent builder as an interface
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* Improve testability of code since stages will most likely be doing a single thing, complying to the [Single Responsibility Principle (SRP)](https://java-design-patterns.com/principles/#single-responsibility-principle)
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## Known uses
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* [java.util.Stream](https://docs.oracle.com/javase/8/docs/api/java/util/stream/package-summary.html)
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* [Maven Build Lifecycle](http://maven.apache.org/guides/introduction/introduction-to-the-lifecycle.html)
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* [Functional Java](https://github.com/functionaljava/functionaljava)
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## Related patterns
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* [Chain of Responsibility](https://java-design-patterns.com/patterns/chain/)
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## Credits
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* [The Pipeline Pattern — for fun and profit](https://medium.com/@aaronweatherall/the-pipeline-pattern-for-fun-and-profit-9b5f43a98130)
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* [The Pipeline design pattern (in Java)](https://medium.com/@deepakbapat/the-pipeline-design-pattern-in-java-831d9ce2fe21)
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* [Pipelines | Microsoft Docs](https://docs.microsoft.com/en-us/previous-versions/msp-n-p/ff963548(v=pandp.10))
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