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Building a Web API

To build an API, the following extensions are necessary:

To add extensions, either just add the dependency to the pom manually or use either of the following commands:

./mvnw quarkus:add-extension -Dextensions="io.quarkus:quarkus-rest-jackson"

quarkus ext add io.quarkus:quarkus-rest-jackson

See the REST guide for more detailed information.

Defining endpoints

Since Quarkus relies on JAX-RS definitions, all usual annotations can be used. Excerpt:

Annotation Description
@Path Specifies the URI path for a resource class or method.
@GET Indicates that the method responds to HTTP GET requests.
@POST Indicates that the method responds to HTTP POST requests.
@PUT Indicates that the method responds to HTTP PUT requests.
@DELETE Indicates that the method responds to HTTP DELETE requests.
@PATCH Indicates that the method responds to HTTP PATCH requests.
@PathParam Binds a method parameter to a URI template variable.
@QueryParam Binds a method parameter to a query string parameter.
@DefaultValue Specifies a default value for a parameter if it is not provided in the request.

TASK 2.1

Create a JAX-RS resource on the path /messages for the following POJO:

public static class Message {
   public int id;
   public String message;
}

Create the following endpoints:

  • GET to fetch all messages
  • POST to create a message (respond with 201)
  • DELETE to delete a message by id. Ignore any persistence and store created messages in an in memory collection of your choice. Solution: ./solutions/1.1

Validation

Quarkus suggests Hibernate Validator for validating inputs. It's supported via the quarkus-hibernate-validator extension.

To activate validation, annotate the JAX-RS content (request body, query or path parameter) with @jakarta.validation.Valid. Enrich the parameters or body fields with specific constraints depending on the rules you want. Multiple constraints can be added to one element as usual.

Example:

@GET
public String hello(@QueryParam("name") @Valid @NotNull String name) {
    return "Hello "+ name +" from Quarkus REST";
}

@POST
public String postGreeting(@Valid @NotNull String message) {
    return message;
}

TASK 2.2

Validate the POST body as follows:

  • id should be >= 0 (use @Min)
  • message should not be blank (use @NotBlank) and between 2 and 10 symbols (use @Size)

Validate the path parameter of the delete method to be >= 0

OpenAPI Support

To add OpenAPI support to your application, simply add the quarkus-smallrye-openapi extension. It recognizes all resources and models and provides an OpenAPI endpoint at /q/openapi. Swagger UI is available under /q/swagger-ui.

The definitions can be extended further manually. For more information, see the guide.