Master Spring Boot 3 Config: @ConfigurationProperties, Constructor Binding & Default Values

Overview

This article announces a Spring Boot 3 case collection (PDF) and provides a step‑by‑step guide on configuration property binding in Spring Boot.

1. @ConfigurationProperties vs @Value

Spring Boot supports two ways to bind configuration properties: @ConfigurationProperties and @Value . Although both work, @ConfigurationProperties is generally recommended because it offers a structured, type‑safe approach.

2. Constructor Binding

2.1 Multiple constructors

When a configuration class defines several constructors, Spring Boot falls back to setter‑based binding. To force a specific constructor, annotate it with @ConstructorBinding . Only one constructor may carry this annotation.

<code>@ConstructorBinding
public PackApp(String title, String version) {
    this.title = title;
    this.version = version;
}
</code>

2.2 Single constructor

If there is only one parameterized constructor, it is used automatically. To prevent constructor binding, you can annotate the constructor with @Autowired or make it private .

<code>@Autowired
public PackApp(MyBean bean) {
    // TODO
}
</code>

2.3 Record types

Constructor binding also works with Java records introduced in JDK 16.

<code>@ConfigurationProperties(prefix = "pack.app")
public record AppRecord(String title, String version, Integer sno) {}
</code>

3. @DefaultValue annotation

3.1 Basic usage

When a property is missing, @DefaultValue supplies a fallback value.

<code>public PackApp(String title, String version,
                @DefaultValue("888") Integer sno) { … }
</code>

3.2 Nested property default

For nested objects, @DefaultValue can create an empty instance instead of null .

<code>public PackApp(String title, String version,
                Integer sno,
                @DefaultValue Security security) { … }
</code>

3.3 Collection defaults

Collections can receive default values as well.

<code>public PackApp(String title, String version,
                Integer sno,
                @DefaultValue({"ADMIN","MGR"}) List<String> roles) { … }
</code>

3.4 Default values in records

Records can also define defaults.

<code>public record AppRecord(String title,
                         String version,
                         @DefaultValue("999") Integer sno) {}
</code>

The article concludes by reminding readers that the PDF collection will be continuously updated and that subscribers receive the source code and full documentation for free.