@ConfigurationProperties

@Data
@ConfigurationProperties("db.mysql")
public class MySQLProperties {
  private String host;
  private Integer port;
  private String db;
}

@Configuration
@EnableConfigurationProperties(MySQLProperties.class)
public class ConfigurationPropertiesConfig {}

***************************
APPLICATION FAILED TO START
***************************

Description:

Failed to bind properties under 'db.mysql.port' to java.lang.Integer:

    Property: db.mysql.port
    Value: "port"
    Origin: class path resource [application.properties] - 5:15
    Reason: failed to convert java.lang.String to java.lang.Integer (caused by java.lang.NumberFormatException: For input string: "port")

Action:

Update your application's configuration

@Configuration
//@EnableConfigurationProperties(MySQLProperties.class)
@ConfigurationPropertiesScan
public class ConfigurationPropertiesConfig {
}

@Getter
@ConfigurationProperties(prefix = "db.mysql")
public class MySQLProperties {

    private final String host;
    private final Integer port;
    private final String db;

    public MySQLProperties(String host, Integer port, String db) {
        this.host = host;
        this.port = port;
        this.db = db;
    }
}

@ConfigurationProperties(prefix = "db.mysql")
@Validated
public class MySQLProperties {

    private final String host;
    private final Integer port;
    private final String db;

    @Min(1)
    @Max(100)
    private final Integer poolSize;

    public MySQLProperties(String host, Integer port, String db, Integer poolSize) {
        this.host = host;
        this.port = port;
        this.db = db;
        this.poolSize = poolSize;
    }
}

***************************
APPLICATION FAILED TO START
***************************

Description:

Binding to target com.example.demo.MySQLProperties failed:

    Property: db.mysql.poolSize
    Value: "1000"
    Origin: class path resource [application.properties] - 6:20
    Reason: 100 이하여야 합니다


Action:

Update your application's configuration