java 49 lines · 5 steps

Feature-flagged beans with Spring @ConditionalOnProperty

Swap an invoice delivery strategy at startup based on a config property, with a safe default.

Explained by highlit

Spring Intermediate feature-flags conditional-beans strategy-pattern configuration-properties dependency-injection

1package com.acme.billing.config;
2 
3import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
4import org.springframework.boot.context.properties.ConfigurationProperties;
5import org.springframework.boot.context.properties.EnableConfigurationProperties;
6import org.springframework.context.annotation.Bean;
7import org.springframework.context.annotation.Configuration;
8 
9@Configuration
10@EnableConfigurationProperties(InvoiceFeatureProperties.class)
11public class InvoiceFeatureConfig {
12 
13    @Bean
14    @ConditionalOnProperty(prefix = "features.invoicing", name = "async-delivery", havingValue = "true")
15    public InvoiceDeliveryStrategy asyncInvoiceDeliveryStrategy(InvoiceMailer mailer,
16                                                               InvoiceFeatureProperties properties) {
17        return new AsyncInvoiceDeliveryStrategy(mailer, properties.getBatchSize());
18    }
19 
20    @Bean
21    @ConditionalOnProperty(prefix = "features.invoicing", name = "async-delivery",
22            havingValue = "false", matchIfMissing = true)
23    public InvoiceDeliveryStrategy syncInvoiceDeliveryStrategy(InvoiceMailer mailer) {
24        return new SyncInvoiceDeliveryStrategy(mailer);
25    }
26}
27 
28@ConfigurationProperties(prefix = "features.invoicing")
29class InvoiceFeatureProperties {
30 
31    private boolean asyncDelivery = false;
32    private int batchSize = 50;
33 
34    public boolean isAsyncDelivery() {
35        return asyncDelivery;
36    }
37 
38    public void setAsyncDelivery(boolean asyncDelivery) {
39        this.asyncDelivery = asyncDelivery;
40    }
41 
42    public int getBatchSize() {
43        return batchSize;
44    }
45 
46    public void setBatchSize(int batchSize) {
47        this.batchSize = batchSize;
48    }
49}

01 / 01

STEP 01

Walkthrough

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Three takeaways

1@ConditionalOnProperty lets one property select which implementation of an interface gets wired.
2Pairing havingValue "true" against "false" with matchIfMissing guarantees exactly one bean always exists.
3Binding external config to a typed properties class keeps tunables like batch size out of your code.

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