# Flow

The class [`Flow`](https://hal.github.io/elemento/apidocs/org/jboss/elemento/flow/Flow.html) provides methods for executing a list of asynchronous tasks in parallel or sequentially or to execute a single task repeatedly as long as certain conditions are met.

See the API documentation of [`org.jboss.elemento.flow`](https://hal.github.io/elemento/apidocs/org/jboss/elemento/flow/package-summary.html) for more details.

## Parallel

```java
// datetime format is "2022-03-31T11:03:39.348365+02:00"
Task<FlowContext> currentTime = context -> fetch("https://worldtimeapi.org/api/timezone/Europe/Berlin")
        .then(Response::json)
        .then(json -> Promise.resolve(Js.<JsPropertyMap<String>>cast(json).get("datetime").substring(11, 23)))
        .then(context::resolve);
double ms = 500 + new Random().nextInt(2000);
Task<FlowContext> delay = context -> new Promise<>((res, __) -> setTimeout(___ -> res.onInvoke(context), ms));

// execute the two tasks in parallel
Flow.parallel(new FlowContext(), List.of(currentTime, delay))
        .subscribe(context -> console.log("Current time: " + context.pop("n/a")));
```

## Sequential

```java
// datetime format is "2022-03-31T11:03:39.348365+02:00"
Task<FlowContext> currentTime = context -> fetch("https://worldtimeapi.org/api/timezone/Europe/Berlin")
        .then(Response::json)
        .then(json -> Promise.resolve(Js.<JsPropertyMap<String>>cast(json).get("datetime").substring(11, 23)))
        .then(context::resolve);
double ms = 500 + new Random().nextInt(2_000);
Task<FlowContext> delay = context -> new Promise<>((res, __) -> setTimeout(___ -> res.onInvoke(context), ms));

// execute the two tasks in sequence and cancel after 1_000 ms
Flow.parallel(new FlowContext(), List.of(currentTime, delay))
        .timeout(1_000)
        .subscribe(context -> console.log("Current time: " + context.pop("n/a")));
```

## Repeated

```java
Task<FlowContext> currentTime = context -> fetch("https://worldtimeapi.org/api/timezone/Europe/Berlin")
        .then(Response::json)
        .then(json -> Promise.resolve(Js.<JsPropertyMap<String>>cast(json).get("datetime").substring(11, 23)))
        .then(context::resolve);

// fetch the current time until the milliseconds end with "0" and cancel after 5 iterations
Flow.repeat(new FlowContext(),currentTime)
        .while_(context -> !context.pop("").endsWith("0"))
        .iterations(5)
        .subscribe(context -> console.log("Current time: " + context.pop("n/a")));
```

## Dependency

Add the following dependency to use `elemento-flow`:

```xml
<dependency>
    <groupId>org.jboss.elemento</groupId>
    <artifactId>elemento-flow</artifactId>
    <version>2.4.11</version>
</dependency>
```

In your GWT module, inherit from `org.jboss.elemento.Flow`:

```xml
<module>
    <inherits name="org.jboss.elemento.Flow"/>
</module>
```


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://hal-console.gitbook.io/elemento/flow.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.