10 Quarkus REST Client Best Practices

Quarkus is a Kubernetes-native Java stack tailored for GraalVM and OpenJDK HotSpot, crafted from the best of breed Java libraries and standards. Quarkus provides a comprehensive set of features to develop, deploy, and manage Java applications.

One of the most important features of Quarkus is its REST client. This article will provide 10 best practices for using the Quarkus REST client. We will discuss how to make the most of the Quarkus REST client, from setting up the client to making efficient requests.

1. Use the @RegisterRestClient annotation to register a REST client

The @RegisterRestClient annotation allows developers to register a REST client as a CDI bean. This makes it easier for the application to access and use the client, since all of its methods are available through dependency injection. Additionally, this annotation also provides additional features such as automatic URL resolution, request/response logging, and more.

Using the @RegisterRestClient annotation is also beneficial because it simplifies the process of creating a REST client. Instead of manually configuring the client, developers can simply annotate their class with the @RegisterRestClient annotation and Quarkus will automatically create the necessary configuration. This saves time and effort, allowing developers to focus on writing code instead of dealing with configuration.

2. Prefer using the Quarkus Rest Client over JAX-RS for simple HTTP requests

The Quarkus Rest Client is a lightweight, reactive client for HTTP requests. It provides an easy-to-use API that allows developers to quickly and efficiently make HTTP requests without having to write complex code. This makes it ideal for simple tasks such as making GET or POST requests.

Unlike JAX-RS, the Quarkus Rest Client does not require any additional configuration or setup. All you need to do is add the dependency to your project and you’re ready to go. Additionally, the Quarkus Rest Client supports asynchronous calls, which can help improve performance by allowing multiple requests to be processed in parallel.

3. Make sure to use the correct media type when sending/receiving data

Using the correct media type ensures that data is sent and received in a format that both parties understand. This helps to ensure that the data is interpreted correctly, which can prevent errors from occurring during communication. For example, if an application sends JSON data but the receiving application expects XML, then the data will not be properly understood and could lead to unexpected results.

To make sure the right media type is used, Quarkus REST Client provides several methods for setting the content-type header when sending requests. These include using the @Produces annotation on the method level or the @ContentType annotation on the parameter level. Additionally, the client also allows users to set the Accept header when making requests, so that the server knows what kind of response it should send back.

4. Set timeouts on all requests to avoid blocking threads

When making requests to external services, there is always a risk that the service may not respond in time. If this happens, the thread will be blocked until either the response arrives or a timeout occurs. This can cause serious performance issues and even lead to application crashes if too many threads are blocked at once.

Setting timeouts on all requests helps to mitigate this issue by ensuring that any request which takes longer than the specified amount of time will automatically fail with an error. This prevents threads from being blocked for too long and keeps the application running smoothly.

To set a timeout when using Quarkus REST Client, you simply need to specify the desired value as part of the configuration. For example, you could use the following code to set a 10 second timeout:

`restClientBuilder.readTimeout(10, TimeUnit.SECONDS);`

This ensures that any requests taking longer than 10 seconds will automatically fail, preventing threads from being blocked for too long.

5. Leverage the Retry and Circuit Breaker features of Quarkus Rest Client

Retry is a feature that allows the client to retry failed requests. This can be useful in cases where there are transient errors, such as network issues or server overloads. By using Retry, the client will automatically attempt to re-send the request until it succeeds or reaches its maximum number of attempts.

Circuit Breaker is another important feature of Quarkus Rest Client. It helps protect against cascading failures by monitoring the success rate of requests and automatically disabling requests when the failure rate exceeds a certain threshold. This prevents further requests from being sent, thus protecting the system from overloading.

Both Retry and Circuit Breaker features help ensure that requests are successful and that the system remains stable even under heavy load. They also provide additional protection against unexpected errors, making them essential for any application using Quarkus REST Client.

6. Avoid hard coding URLs in your code, prefer injecting them as configuration parameters

Hard coding URLs in your code can lead to a number of issues. For example, if the URL changes, you would need to manually update all instances of it throughout your codebase. This is time consuming and error-prone. Additionally, hard coded URLs are not easily configurable for different environments such as development, staging, and production.

Using configuration parameters instead allows you to define the URL once in an external configuration file or environment variable. This makes it easier to manage and maintain, since any changes only need to be made in one place. It also makes it simpler to switch between different environments, since the same code can be used with different configurations.

Quarkus REST Client provides several ways to inject configuration parameters into your code. You can use the @ConfigProperty annotation to inject values from application configuration files, or the @EnvVariable annotation to inject values from environment variables. Both annotations support default values, so that if the parameter is not set, the default value will be used.

7. Implement custom serialization/deserialization logic where needed

When using the Quarkus REST Client, it is important to ensure that data is serialized and deserialized correctly. This means that when sending a request, the data must be in the correct format for the server to understand it, and when receiving a response, the data must be in the correct format for the client to process it. Custom serialization/deserialization logic can help with this by allowing developers to define how they want their data to be formatted before sending or after receiving it.

Custom serialization/deserialization logic can also be used to add additional features such as validation, encryption, compression, etc. For example, if a developer wants to make sure that all requests sent from the client are encrypted, they can use custom serialization logic to encrypt the data before sending it. Similarly, if a developer wants to compress responses received from the server, they can use custom deserialization logic to decompress the data after receiving it.

8. Handle errors gracefully and provide meaningful error messages

When an error occurs, it is important to provide meaningful feedback to the user. This helps them understand what went wrong and how they can fix it. Without this information, users may be left confused or frustrated. By providing a clear explanation of the issue, users are more likely to take corrective action quickly.

Error messages should also be tailored to the context in which they occur. For example, if an API call fails due to authentication issues, the message should explain why authentication failed and how to resolve it. If the problem is related to data validation, the message should explain what data was invalid and how to correct it.

It’s also important to handle errors gracefully. This means that when an error occurs, the application should not crash or become unresponsive. Instead, it should continue running and display an appropriate error message. This ensures that the user experience remains positive even when something goes wrong.

To ensure that Quarkus REST Client handles errors gracefully and provides meaningful error messages, developers should use exception handling techniques such as try-catch blocks. These allow for specific code to be executed when an error occurs, allowing developers to customize the response accordingly. Additionally, developers should make sure to log all errors so that they can be tracked and addressed appropriately.

9. Log responses from the server for debugging purposes

Logging server responses is a great way to quickly identify and troubleshoot any issues that may arise when using the Quarkus REST Client. By logging the response from the server, developers can easily see what data was sent back by the server, as well as any errors or exceptions that were encountered during the request-response cycle. This allows them to pinpoint exactly where the issue lies and take corrective action accordingly.

The Quarkus REST Client provides several methods for logging server responses. The most common approach is to use the Logger class, which allows developers to log messages at different levels (e.g., INFO, WARN, ERROR). Additionally, developers can also use the ResponseInterceptor interface to intercept and log the response before it is returned to the client. Finally, developers can also use the RequestFilter interface to filter out certain requests and log their responses separately.

10. Monitor performance metrics such as request latency and throughput

Request latency is the amount of time it takes for a request to be processed and responded to. Monitoring this metric can help identify any bottlenecks in the system, such as slow response times due to network congestion or inefficient code. It also helps to ensure that requests are being handled quickly and efficiently.

Throughput is the number of requests that can be processed within a given period of time. This metric is important because it allows developers to measure how well their application is performing under load. By monitoring throughput, they can determine if their application is able to handle the expected traffic levels without becoming overloaded.

Monitoring these metrics can be done using various tools, such as Grafana or Prometheus. These tools allow developers to track performance over time and make adjustments as needed. They can also be used to set up alerts when certain thresholds are exceeded, so that issues can be addressed before they become serious problems.