Exercises

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In these exercises, you’ll practice some of the concepts taught in this module.

First, either create a new Java project, adding the reactor-bom and reactor-core dependencies to your build file (Maven or Gradle) or use the stub you can find at: https://github.com/eh3rrera/project-reactor-course/tree/main/07/before/reactor-demo-exercises.

I’ll give you the instructions (and sometimes hints) so you can put all the code together in the main method of a class and observe the output.

Here you can find the solution for the coding exercises: https://github.com/eh3rrera/project-reactor-course/tree/main/07/after/reactor-demo-exercises.

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Exercise 1

In this coding exercise, you’ll create a Flux that uses the contextWrite(ContextView) method to enrich the context with additional data.

1. Given the following code:

    import reactor.core.publisher.Flux;
   
    public class Exercise01 {
        public static void main(String[] args) {
            Flux<Integer> numbers = Flux.range(1, 5);
            String key = "divider";
            double value = 10.0;
            double defaultValue = 1.0;
   
            // TODO: Divide each emitted number by the "divider" value from the context
            Flux<Double> contextualizedNumbers = null;
   
            // TODO: Add to the Context the key-value pair with the variables of the same name
            // TODO: Subscribe to contextualizedNumbers
        }
    }
   

2. Use the transformDeferredContextual method to divide each emitted number of numbers by the "divider" value from the context, using the default value defined by the variable defaultValue.
3. Use the contextWrite(ContextView) method to enrich the context with a key-value pair, using the variables key and value.
4. Subscribe to contextualizedNumbers printing the emitted values.
5. Run the Exercise01 class and analyze the output.

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Exercise 2

In this coding exercise, you’ll create a Flux that uses the contextWrite(Function<Context, Context>) method to enrich the context with additional data.

1. Given the following code:

    import reactor.core.publisher.Flux;
   
    public class Exercise02 {
        public static void main(String[] args) {
            Flux<Integer> numbers = Flux.range(1, 5);
            String key = "multiplier";
            int value = 3;
            int defaultValue = 1;
   
            // TODO: Multiply each emitted number by the "multiplier" value from the context
            Flux<Integer> contextualizedNumbers = null;
   
            //  TODO: Add to the Context the key-value pair with the variables of the same name
            //  TODO: Subscribe to contextualizedNumbers
        }
    }
   

2. Use flatMap and Mono.deferContextual to multiply each emitted number of numbers by the "multiplier" value from the context, using the default value defined by the variable defaultValue.
3. Use the contextWrite(Function<Context, Context>) method to enrich the context with a key-value pair, using the variables key and value.
4. Subscribe to contextualizedNumbers printing the emitted values.
5. Run the Exercise02 class and analyze the output.

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Exercise 3

In this coding exercise, you’ll use the transformDeferredContextual method to apply a transformation to a Mono while considering the context.

1. Given the following code:

    import reactor.core.publisher.Mono;
   
    public class Exercise03 {
        public static void main(String[] args) {
            Mono<String> greetingMono = Mono.just("Hello");
            String key = "username";
   
            // TODO: Append the value of the "username" key from the context to the emitted string
            Mono<String> contextualizedGreetingMono = null;
   
            //  TODO: Add to the Context the value "Alice"
            //  TODO: Subscribe to contextualizedNumbers
   
            //  TODO: Add to the Context the value "Bob"
            //  TODO: Subscribe again to contextualizedNumbers
        }
    }
   

2. Use transformDeferredContextual to append the value of the "username" key from the context to the string emitted by greetingMono.
3. Use the contextWrite(Function<Context, Context>) method to enrich the context with a key-value pair, using the variable key as key, and "Alice" as value.
4. Subscribe to contextualizedNumbers printing the emitted value.
5. One more time, use the contextWrite(Function<Context, Context>) method to enrich the context with a key-value pair, using the variable key as key, and "Bob" as value.
6. Subscribe again to contextualizedNumbers printing the emitted value.
7. Run the Exercise03 class and analyze the output.

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