Spring Top – Temp

Get started with Spring 5 and Spring Boot 2, through the reference Learn Spring course:

>> LEARN SPRING
Lightrun – Third Party Code

We rely on other people’s code in our own work. Every day. It might be the language you’re writing in, the framework you’re building on, or some esoteric piece of software that does one thing so well you never found the need to implement it yourself.

The problem is, of course, when things fall apart in production - debugging the implementation of a 3rd party library you have no intimate knowledge of is, to say the least, tricky. It’s difficult to understand what talks to what and, specifically, which part of the underlying library is at fault.

Lightrun is a new kind of debugger.

It's one geared specifically towards real-life production environments. Using Lightrun, you can drill down into running applications, including 3rd party dependencies, with real-time logs, snapshots, and metrics. No hotfixes, redeployments, or restarts required.

Learn more in this quick, 5-minute Lightrun tutorial:

>> The Essential List of Spring Boot Annotations and Their Use Cases

1. Overview

In this tutorial, we're going to learn about Spring's @Order annotation. The @Order annotation defines the sorting order of an annotated component or bean.

It has an optional value argument which determines the order of the component; the default value is Ordered.LOWEST_PRECEDENCE. This marks that the component has the lowest priority among all other ordered components.

Similarly, the value Ordered.HIGHEST_PRECEDENCE can be used for overriding the highest priority among components.

2. When to Use @Order

Before Spring 4.0, the @Order annotation was used only for the AspectJ execution order. It means the highest order advice will run first.

Since Spring 4.0, it supports the ordering of injected components to a collection. As a result, Spring will inject the auto-wired beans of the same type based on their order value.

Let's explore it with a quick example.

3. How to Use @Order

First of all, let's set up our project with the relevant interface and classes.

3.1. Interface Creation

Let's create the Rating interface that determines the rating of a product:

public interface Rating {
    int getRating();
}

3.2. Components Creation

Finally, let's create three components that define the ratings of some products:

@Component
@Order(1)
public class Excellent implements Rating {

    @Override
    public int getRating() {
        return 1;
    }
}

@Component
@Order(2)
public class Good implements Rating {

    @Override
    public int getRating() {
        return 2;
    }
}

@Component
@Order(Ordered.LOWEST_PRECEDENCE)
public class Average implements Rating {

    @Override
    public int getRating() {
        return 3;
    }
}

Note that the Average class has the lowest priority because of its overridden value.

4. Testing Our Example

Up until now, we've created all the required components and the interface to test the @Order annotation. Now, let's test it to confirm that it works as expected:

public class RatingRetrieverUnitTest { 
    
    @Autowired
    private List<Rating> ratings;
    
    @Test
    public void givenOrder_whenInjected_thenByOrderValue() {
        assertThat(ratings.get(0).getRating(), is(equalTo(1)));
        assertThat(ratings.get(1).getRating(), is(equalTo(2)));
        assertThat(ratings.get(2).getRating(), is(equalTo(3)));
    }
}

5. Conclusion

We've learned about the @Order annotation in this quick article. We can find the application of @Order in various use cases – where the ordering of the auto-wired components matter. One example is the Spring's request filters.

Due to its influence on injection precedence, it may seem like it might influence the singleton startup order also. But in contrast, the dependency relationships and @DependsOn declarations determine the singleton startup order.

All examples mentioned in this tutorial can be found over on Github.

Spring bottom

Get started with Spring 5 and Spring Boot 2, through the Learn Spring course:

>> THE COURSE
Generic footer banner
Comments are closed on this article!