Archive: August 2018

Micronaut Mastery: Using Specific Configuration Properties For HTTP Client

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Hubert Klein Ikkink

One of the (many) great features of Micronaut is the HTTP client. We use the @Client annotation to inject a low-level HTTP client. Or we define a declarative HTTP client based on an interface, for which Micronaut will generate an implementation. The @Client annotation supports the configuration parameter to reference a configuration class with configuration properties for the HTTP client. The configuration class extends HttpClientConfiguration to support for example the configuration of timeouts and connection pooling. We can add our own configuration properties as well and use them in our application.

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Micronaut Mastery: Using Stubs For Testing

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Hubert Klein Ikkink

Writing tests is always a good idea when developing an application. Micronaut makes it very easy to write tests. Using the @Client annotation we can generate a client for our REST resources that uses HTTP. Starting up a Micronaut application is so fast we can run our actual application in our tests. And using dependency injection we can replace components from the production application with stubs in our tests.

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Micronaut Mastery: Return Response Based On HTTP Accept Header

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Hubert Klein Ikkink

Suppose we want our controller methods to return a JSON response when the HTTP Accept header is set to application/json and XML when the Accept header is set to application/xml. We can access the values of HTTP headers in our controller methods by adding an argument of type HttpHeaders to our method definition and Micronaut will add all HTTP headers with their values as HttpHeaders object when we run the application. In our method we can check the value of the Accept header and return a different value based on the header value.

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Micronaut Mastery: Add Custom Health Indicator

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Hubert Klein Ikkink

When we add the io.micronaut:management dependency to our Micronaut application we get, among other things, a /health endpoint. We must enable it in our application configuration where we can also configure how much information is shown and if we want to secure the endpoint. Micronaut has some built-in health indicators, some of which are only available based on certain conditions. For example there is a disk space health indicator that will return a status of DOWN when the free disk space is less than a (configurable) threshold. If we would have one or more DataSource beans for database access in our application context a health indicator is added as well to show if the database(s) are available or not.

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Micronaut Mastery: Add Build Info To Info Endpoint

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Hubert Klein Ikkink

Micronaut has some built-in management endpoints to get information, a list of beans, health checks and more. To enable the endpoints we must add the dependency io.micronaut:management to our application. Then we can add configuration properties to enable the different endpoints. The /info endpoint gathers information from several sources with properties. If we want to add build information we must create a file build-info.properties with information and Micronaut will automatically add the properties from the file to the /info endpoint.

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Micronaut Mastery: Decode JSON Using Custom Constructor Without Jackson Annotations

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Hubert Klein Ikkink

Micronaut uses Jackson to encode objects to JSON and decode JSON to objects. Micronaut adds a Jackson ObjectMapper bean to the application context with all configuration to work properly. Jackson can by default populate an object with values from JSON as the class has a no argument constructor and the properties can be accessed. But if our class doesn’t have a no argument constructor we need to use the @JsonCreator and @JsonProperty annotations to help Jackson. We can use these annotation on the constructor with arguments that is used to create an object.

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Micronaut Mastery: Using Reactor Mono And Flux

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Hubert Klein Ikkink

Micronaut is reactive by nature and uses RxJava2 as implementation for the Reactive Streams API by default. RxJava2 is on the compile classpath by default, but we can easily use Project Reactor as implementation of the Reactive Streams API. This allows us to use the Reactor types Mono and Flux. These types are also used by Spring’s Webflux framework and makes a transition from Webflux to Micronaut very easy.

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