Note
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This repository contains the guide documentation source. To view the guide in published form, view it on the Open Liberty website. |
Explore how to document and filter RESTful APIs from code or static files by using MicroProfile OpenAPI.
You will learn how to document and filter RESTful APIs from annotations, POJOs, and static OpenAPI files by using MicroProfile OpenAPI.
The OpenAPI specification, previously known as the Swagger specification, defines a standard interface for documenting and exposing RESTful APIs. This specification allows both humans and computers to understand or process the functionalities of services without requiring direct access to underlying source code or documentation. The MicroProfile OpenAPI specification provides a set of Java interfaces and programming models that allow Java developers to natively produce OpenAPI v3 documents from their JAX-RS applications.
You will document the RESTful APIs of the provided inventory
service, which serves two endpoints,
inventory/systems
and inventory/properties
. These two endpoints function the same way as in the
other MicroProfile guides.
Before you proceed, note that the 1.0 version of the MicroProfile OpenAPI specification does
not define how the /openapi
endpoint may be partitioned in the event of multiple JAX-RS applications
running on the same server. In other words, you must stick to one JAX-RS application per server instance
as the behaviour for handling multiple applications is currently undefined.
The finish
directory in the root directory of this guide contains the fully documented inventory
service. Feel free to give it a try before you proceed.
To try out the service, navigate to the finish
directory and then run the Maven install
and
liberty:start-server
goals to build and run the service in Open Liberty:
mvn install liberty:start-server
Next, point your browser to the http://localhost:9080/openapi URL and you’ll see the RESTful APIs of the inventory
service. You can also point to the http://localhost:9080/openapi/ui URL for a more interactive view of the deployed APIs.
This UI is built from the Open Source Swagger UI and renders the generated /openapi
document into a very user friendly page.
When you are done checking out the service and its APIs, stop Open Liberty:
mvn liberty:stop-server
You can generate an OpenAPI document in various ways. First, because all JAX-RS annotations are processed by default, you can augment your existing JAX-RS annotations with OpenAPI annotations to enrich your APIs with a minimal amount of work. Second, you can use a set of predefined models to manually create all elements of the OpenAPI tree. Finally, you can filter various elements of the OpenAPI tree, changing them to your liking or removing them entirely.
Before you proceed, deploy the inventory
service to see the bare-bones OpenAPI document that is generated.
To deploy the inventory
service, navigate to the start
directory and run the Maven install
phase and the liberty:start-server
goal:
mvn install liberty:start-server
The install
phase builds the application and packages it into the target/mp-openapi.war
file.
It also downloads Open Liberty into the target/liberty/wlp
directory and configures it to run the
application. The liberty:start-server
goal starts an Open Liberty server instance.
Because the JAX-RS framework handles basic API generation for JAX-RS annotations, a skeleton OpenAPI
tree will be generated from the inventory
service. You can use this tree as a starting point and
augment it with annotations and code to produce a complete OpenAPI document.
Now, point to the http://localhost:9080/openapi URL to see the generated OpenAPI tree. You can also point to the http://localhost:9080/openapi/ui URL for a more interactive view of the APIs.
Because all JAX-RS annotations are processed by default, you can augment the existing code with OpenAPI annotations without needing to rewrite portions of the OpenAPI document that are already covered by the JAX-RS framework.
Update theInventoryResource
class.src/main/java/io/openliberty/guides/inventory/InventoryResource.java
Add OpenAPI annotations to the two JAX-RS methods, getPropertiesForHost()
and listContents()
.
InventoryResource.java
link:finish/src/main/java/io/openliberty/guides/inventory/InventoryResource.java[role=include]
Clearly, there are many more annotations now, so let’s break them down:
Annotation | Description |
---|---|
|
A container for multiple responses from an API operation. This annotation is optional, but it can be helpful to organize a method with multiple responses. |
|
Describes a single response from an API operation. |
|
Provides a schema and examples for a particular media type. |
|
Defines the input and output data types. |
|
Describes a single API operation on a path. |
|
Describes a single operation parameter. |
At this point, you can run the the following command to rebuild the application.
mvn compile
Then, refresh the http://localhost:9080/openapi URL to see the updated OpenAPI tree. The two endpoints at which your JAX-RS methods are served are now more meaningful:
/inventory/systems/{hostname}:
get:
summary: Get JVM system properties for particular host
description: Retrieves and returns the JVM system properties from the system
service running on the particular host.
operationId: getPropertiesForHost
parameters:
- name: hostname
in: path
description: The host for whom to retrieve the JVM system properties for.
required: true
schema:
type: string
example: foo
responses:
404:
description: Invalid hostname or the system service may not be running on
the particular host.
content:
text/plain: {}
200:
description: JVM system properties of a particular host.
content:
application/json:
schema:
$ref: '#/components/schemas/Properties'
/inventory/systems:
get:
summary: List inventory contents.
description: Returns the currently stored host:properties pairs in the inventory.
operationId: listContents
responses:
200:
description: host:properties pairs stored in the inventory.
content:
application/json:
schema:
$ref: '#/components/schemas/InventoryList'
OpenAPI annotations can also be added to POJOs to describe what they represent. Currently, your OpenAPI
document doesn’t have a very meaningful description of the InventoryList
POJO and hence it’s very
difficult to tell exactly what that POJO is used for. To describe the InventoryList
POJO in more detail, augment the
src/main/java/io/openliberty/guides/inventory/model/InventoryList.java
file with some OpenAPI annotations.
Update theInventoryList
class.src/main/java/io/openliberty/guides/inventory/model/InventoryList.java
Add OpenAPI annotations to the InventoryList
class and the systems
variable.
InventoryList.java
link:finish/src/main/java/io/openliberty/guides/inventory/model/InventoryList.java[role=include]
Likewise, annotate the src/main/java/io/openliberty/guides/inventory/model/SystemData.java
POJO,
which is referenced in the InventoryList
class.
Update theSystemData
class.src/main/java/io/openliberty/guides/inventory/model/SystemData.java
Add OpenAPI annotations to the SystemData
class, the hostname
variable and the properties
variable.
SystemData.java
link:finish/src/main/java/io/openliberty/guides/inventory/model/SystemData.java[role=include]
Again, run the following command and refresh the http://localhost:9080/openapi URL to see the updated OpenAPI tree.
mvn compile
components:
schemas:
InventoryList:
required:
- systems
type: object
properties:
systems:
type: array
items:
$ref: '#/components/schemas/SystemData'
total:
type: integer
description: POJO that represents the inventory contents.
SystemData:
required:
- hostname
- properties
type: object
properties:
hostname:
type: string
properties:
type: object
additionalProperties:
type: string
description: POJO that represents a single inventory entry.
Properties:
type: object
additionalProperties:
type: string
Filtering of certain elements and fields of the generated OpenAPI document can be done by using the
OASFilter
interface.
Create theInventoryOASFilter
class.src/main/java/io/openliberty/guides/inventory/filter/InventoryOASFilter.java
InventoryOASFilter.java
link:finish/src/main/java/io/openliberty/guides/inventory/filter/InventoryOASFilter.java[role=include]
The filterAPIResponse()
method allows filtering of APIResponse
elements. When you
override this method, it will be called once for every APIResponse
element in the OpenAPI tree.
In this case, you are matching the 404
response that is returned by the /inventory/systems/{hostname}
endpoint and setting the previously missing description. To remove an APIResponse
element
or another filterable element, simply return null
.
The filterOpenAPI()
method allows filtering of the singleton OpenAPI
element. Unlike other filter
methods, when you override filterOpenAPI()
, it is called only once as the last method
for a particular filter. Hence, make sure that it doesn’t override any other filter operations that are
called before it. Your current OpenAPI document doesn’t provide much information on the application
itself or on what server and port it runs on. This information is usually provided in the info
and servers
elements, which are currently missing. Use the OASFactory
class to manually set these
and other elements of the OpenAPI tree from the org.eclipse.microprofile.openapi.models
package. The OpenAPI
element is the only element that cannot be removed since that would mean
removing the whole OpenAPI tree.
Each filtering method is called once for each corresponding element in the model tree. You can think of each method as a callback for various key OpenAPI elements.
Before you can use the filter class that you created, you need to create the microprofile-config.properties
file.
Create the configuration file.
src/main/webapp/META-INF/microprofile-config.properties
microprofile-config.properties
link:finish/src/main/webapp/META-INF/microprofile-config.properties[role=include]
This configuration file is picked up automatically by MicroProfile Config and registers your filter
by passing in the fully qualified name of the filter class into the mp.openapi.filter
property.
Finally, run the following command and refresh the http://localhost:9080/openapi URL to see the updated OpenAPI tree.
mvn compile
info:
title: Inventory App
description: App for storing JVM system properties of various hosts.
license:
name: Eclipse Public License - v 1.0
url: https://www.eclipse.org/legal/epl-v10.html
version: 1.0.0
servers:
- url: http://localhost:{port}
description: Simple Open Liberty.
variables:
port:
default: "9080"
description: Server HTTP port.
404:
description: Invalid hostname or the system service may not be running on
the particular host.
content:
text/plain: {}
For more information about which elements you can filter, see the MicroProfile API.
To learn more about MicroProfile Config, visit the MicroProfile Config GitHub repository and try one of the MicroProfile Config guides.
As an alternative to generating the OpenAPI model tree from code, you can provide a valid pregenerated
OpenAPI document to describe your APIs. This document must be named openapi
with a yml
, yaml
, or json
extension and be placed under the META-INF
directory. Depending on the scenario, the document
might be fully or partially complete. If the document is fully complete, then you can disable
annotation scanning entirely by setting the mp.openapi.scan.disable
MicroProfile Config property to true
.
If the document is partially complete, then you can augment it with code.
You can find a complete OpenAPI document in the src/main/webapp/META-INF/openapi.yaml
file.
This document is the same as your current OpenAPI document with additional APIs for the /inventory/properties
endpoint. To make use of this document, open this document in your favorite text editor and uncomment
all of its lines.
Update the OpenAPI document file.
src/main/webapp/META-INF/openapi.yaml
Uncomment all the lines in the openapi.yaml
file.
openapi.yaml
link:finish/src/main/webapp/META-INF/openapi.yaml[role=include]
Since this document is complete, you can also set the mp.openapi.scan.disable
property
to true
in the src/main/webapp/META-INF/microprofile-config.properties
file.
Update the configuration file.
src/main/webapp/META-INF/microprofile-config.properties
Add and set the mp.openapi.scan.disable
property to true
.
microprofile-config.properties
link:finish/src/main/webapp/META-INF/microprofile-config.properties[role=include]
Run the following command and refresh the http://localhost:9080/openapi URL to see the updated OpenAPI tree.
mvn compile
/inventory/properties:
get:
operationId: getProperties
responses:
200:
description: JVM system properties of the host running this service.
content:
application/json:
schema:
type: object
additionalProperties:
type: string
No automated tests are provided to verify the correctness of the generated OpenAPI document. Manually verify the document by visiting the http://localhost:9080/openapi or the http://localhost:9080/openapi/ui URL.
A few tests are included for you to test the basic functionality of the inventory
service. If a test
failure occurs, then you might have introduced a bug into the code. These tests will run automatically
as a part of the Maven build process when you run the following command.
mvn install
You can also run these
tests separately from the build by using the following command, but first make sure that the server is stopped.If the server is still running from the previous steps, stop it using the Maven liberty:stop-server
goal from command line in the start
directory:
mvn liberty:stop-server
Then, verify that the tests pass using the Maven verify
goal:
mvn verify
You have just documented and filtered the APIs of the inventory
service from both the code and a static
file by using MicroProfile OpenAPI in Open Liberty.
Feel free to try one of the related MicroProfile guides. They demonstrate additional technologies that you can learn and expand on top of what you built here.
For more in-depth examples of MicroProfile OpenAPI, try one of the demo applications available in the MicroProfile OpenAPI GitHub repository.