5 Essential Spring Boot 3 Techniques for Validating and Customizing Configuration Properties

Environment: Spring Boot 3.0.9

1. Validate Property Configuration

The @ConfigurationProperties annotation binds configuration properties to a Java object, and combined with @Validated it enables safe validation of those properties.

<code>@ConfigurationProperties(prefix = "pack.bank")
@Validated
public class ArmyProperties {
    private String publicKey;
    @NotEmpty(message = "主机不能为空")
    private String host;
    private Integer port;
    // @ByteLength is a custom annotation
    @ByteLength(leng = 6, message = "发送方系统节点号只能为6个字节")
    private String sendNo;
    @ByteLength(leng = 6, message = "接收方系统节点号只能为6个字节")
    private String receiveNo;
    /**是否加密*/
    @EnumValue(intValues = {0, 1}, message = "是否加密只能是0或1")
    private Integer cipher;
}</code>

This approach prevents incorrect configurations; the application will fail to start if validation errors occur.

2. Validate Missing Properties

The @Value annotation injects configuration values into beans. If the property is absent, startup fails.

<code>@Value("${pack.name}")
private String name;</code>

Provide a default value to avoid errors:

<code>@Value("${pack.name:}")
private String name;</code>

Alternatively, configure a PropertySourcesPlaceholderConfigurer bean to ignore unresolved placeholders:

<code>@Bean
public static PropertySourcesPlaceholderConfigurer propertySourcesPlaceholderConfigurer() {
    PropertySourcesPlaceholderConfigurer configurer = new PropertySourcesPlaceholderConfigurer();
    configurer.setIgnoreUnresolvablePlaceholders(true);
    return configurer;
}</code>

3. Custom Property Source

You can add a custom property source to the Spring Environment :

<code>public class PackEnvironmentPostProcessor implements EnvironmentPostProcessor {
    @Override
    public void postProcessEnvironment(ConfigurableEnvironment environment, SpringApplication application) {
        Map<String, Object> source = new HashMap<>();
        source.put("pack.name", "中国🇨🇳");
        PropertySource<?> propertySource = new MapPropertySource("pack", source);
        environment.getPropertySources().addLast(propertySource);
    }
}</code>

Register the processor in META-INF/spring.factories :

<code>org.springframework.boot.env.EnvironmentPostProcessor=\
com.pack.PackEnvironmentPostProcessor</code>

4. Enforce Required Properties

Mark properties that must be present by setting required properties in the environment:

<code>public class PackEnvironmentPostProcessor implements EnvironmentPostProcessor {
    @Override
    public void postProcessEnvironment(ConfigurableEnvironment environment, SpringApplication application) {
        environment.setRequiredProperties("pack.version");
    }
}</code>

If pack.version is missing, the application will fail to start.

5. YML File Parsing

Spring Boot provides utilities to load custom YML files as different property sources:

<code>// Load as PropertySource
YamlPropertySourceLoader loader = new YamlPropertySourceLoader();
List&lt;PropertySource&lt;?&gt;&gt; sources = loader.load("pack", new ClassPathResource("pack.yml"));

// Load as Map
YamlMapFactoryBean mapFactory = new YamlMapFactoryBean();
mapFactory.setResources(new ClassPathResource("com/pack/yml/loader/pack.yml"));

// Load as Properties
YamlPropertiesFactoryBean propertiesFactory = new YamlPropertiesFactoryBean();
propertiesFactory.setResources(new ClassPathResource("com/pack/yml/loader/pack.yml"));</code>

These five tips help you manage configuration properties more safely and flexibly in Spring Boot applications.