As a developer, you are likely aware of the importance of configuration in your application. Configuration files provide a way to set values that control how your application behaves. Spring Boot makes it easy to work with configuration properties by providing a set of tools to work with them.
In this article, we will take a look at what Spring Boot configuration properties are and how to work with them. We will also look at some of the gotchas that you might encounter when working with configuration properties.
Spring Boot configuration properties are key/value pairs that can be used to configure Spring Boot applications. They can be used to set values for various application settings such as the database connection string, application name, and server port. Configuration properties can be set in a number of different ways, including via environment variables, system properties, and command-line arguments.
Spring Boot provides a number of ways to work with configuration properties. In this section, we will take a look at some of the most common ways to work with configuration properties.
One way to work with configuration properties is to use the @ConfigurationProperties
annotation. This annotation can be used on a class to bind configuration properties to fields in the class. For example, the following class would bind the spring.datasource.url
property to the url
field:
@ConfigurationProperties(prefix = "spring.datasource")
public class DataSourceConfig {
private String url;
public String getUrl() {
return url;
}
public void setUrl(String url) {
this.url = url;
}
}
To use this class, you would need to add it as a bean in your Spring Boot application:
@SpringBootApplication
public class Application {
public static void main(String[] args) {
SpringApplication.run(Application.class, args);
}
@Bean
public DataSourceConfig dataSourceConfig() {
return new DataSourceConfig();
}
}
Another way to work with configuration properties is to use the Environment
abstraction. This abstraction provides a way to access configuration properties without having to know the specific property names. For example, the following code would get the value of the spring.datasource.url
property:
@SpringBootApplication
public class Application {
public static void main(String[] args) {
SpringApplication.run(Application.class, args);
}
@Autowired
private Environment environment;
@PostConstruct
public void init() {
String dataSourceUrl = environment.getProperty("spring.datasource.url");
}
}
Another way to work with configuration properties is to use the @Value
annotation. This annotation can be used on fields to inject configuration property values. For example, the following code would inject the value of the spring.datasource.url
property into the url
field:
@SpringBootApplication
public class Application {
@Value("${spring.datasource.url}")
private String url;
public static void main(String[] args) {
SpringApplication.run(Application.class, args);
}
}
There are a few gotchas that you might encounter when working with Spring Boot configuration properties. In this section, we will take a look at some of the most common ones.
Spring Boot configuration properties are case-sensitive. This means that the property spring.datasource.url
is not the same as the property spring.datasource.URL
. If you are having trouble getting a property to work, make sure that you are using the correct case.
Spring Boot configuration properties are not resolved until the application is started. This means that if you try to access a property in your application's main
method, it will not be resolved. For example, the following code will not work:
@SpringBootApplication
public class Application {
public static void main(String[] args) {
String dataSourceUrl = System.getProperty("spring.datasource.url");
SpringApplication.run(Application.class, args);
}
}
To work around this, you can use the @PostConstruct
annotation. This annotation can be used on a method to indicate that it should be called after the properties have been resolved. For example:
@SpringBootApplication
public class Application {
public static void main(String[] args) {
SpringApplication.run(Application.class, args);
}
@PostConstruct
public void init() {
String dataSourceUrl = System.getProperty("spring.datasource.url");
}
}
Another gotcha to be aware of is that properties are not resolved until the application context is initialized. This means that if you try to access a property in a @Configuration
class, it will not be resolved. For example, the following code will not work:
@Configuration
public class MyConfig {
@Value("${spring.datasource.url}")
private String url;
}
To work around this, you can use the Environment
abstraction. For example:
@Configuration
public class MyConfig {
@Autowired
private Environment environment;
@PostConstruct
public void init() {
String dataSourceUrl = environment.getProperty("spring.datasource.url");
}
}
Another gotcha to be aware of is that properties are not resolved until the application is fully started. This means that if you try to access a property in a @Bean
method, it will not be resolved. For example, the following code will not work:
@Configuration
public class MyConfig {
@Bean
public DataSource dataSource() {
String url = System.getProperty("spring.datasource.url");
// ...
}
}
To work around this, you can use the Environment
abstraction. For example:
@Configuration
public class MyConfig {
@Autowired
private Environment environment;
@Bean
public DataSource dataSource() {
String url = environment.getProperty("spring.datasource.url");
// ...
}
}
In this article, we have looked at what Spring Boot configuration properties are and how to work with them. We have also looked at some of the gotchas that you might encounter when working with configuration properties.
Configuring Spring Boot applications can be tricky, but hopefully, this article has given you the information you need to get started.