Micronaut

Micronaut Mastery: Configuration Property Name Is Lowercased And Hyphen Separated

Posted on by  
Hubert Klein Ikkink

In Micronaut we can inject configuration properties in different ways into our beans. We can use for example the @Value annotation using a string value with a placeholder for the configuration property name. If we don’t want to use a placeholder we can also use the @Property annotation and set the name attribute to the configuration property name. We have to pay attention to the format of the configuration property name we use. If we refer to a configuration property name using @Value or @Property we must use lowercased and hyphen separated names (also known as kebab casing). Even if the name of the configuration property is camel cased in the configuration file. For example if we have a configuration property sample.theAnswer in our application.properties file, we must use the name sample.the-answer to get the value.

Continue reading →

Micronaut Mastery: Running Code On Startup

Posted on by  
Hubert Klein Ikkink

When our Micronaut application starts we can listen for the ServiceStartedEvent event and write code that needs to run when the event is fired. We can write a bean that implements the ApplicationEventListener interface with the type ServiceStartedEvent. Or we can use the @EventListener annotation on our method with code we want to run on startup. If the execution of the code can take a while we can also add the @Async annotation to the method, so Micronaut can execute the code on a separate thread.

Continue reading →

Micronaut Mastery: Change The Default Package For Generated Classes

Posted on by  
Hubert Klein Ikkink

When we use the Micronaut command line commands to generate controllers, beans and more, the classes will have a default package name. We can use a fully qualified package name for the class we want to generate, but when we only define a class name, Micronaut will use a default package name automatically. We can set the default package for an application when we first create an application with the create-app command. But we can also alter the default package name for an existing Micronaut application.

Continue reading →

Micronaut Mastery: Using Stubs For Testing

Posted on by  
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.

Continue reading →

Micronaut Mastery: Return Response Based On HTTP Accept Header

Posted on by  
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.

Continue reading →

Micronaut Mastery: Add Custom Health Indicator

Posted on by  
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.

Continue reading →

Micronaut Mastery: Add Build Info To Info Endpoint

Posted on by  
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.

Continue reading →

Micronaut Mastery: Decode JSON Using Custom Constructor Without Jackson Annotations

Posted on by  
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.

Continue reading →

shadow-left