Differences between @Value annotation and the Environment API?

Question

Are there any significant differences between injecting fields of a class with @Value annotation and looking them up using the Spring Environment API? Is one preferable over the other (and under what circumstances)?

Example Using @Value:

class Config {
    @Value("${db.driverClassName}")
    private String driverClassName;

    @Value("${db.url}")
    private String url;

    @Value("${db.username}")
    private String username;

    @Value("${db.password}")
    private String password;

    @Bean
    public javax.sql.DataSource dataSource(){

        PoolProperties poolProperties = new PoolProperties();
        poolProperties.setDriverClassName(driverClassName);
        poolProperties.setUrl(url);         
        poolProperties.setUsername(username);
        poolProperties.setPassword(password);

        return new org.apache.tomcat.jdbc.pool.DataSource(poolProperties);

    }

}

Example Using Environment API:

class Config {
    @Autowired
    private Environment environment;

    @Bean
    public javax.sql.DataSource dataSource(){

        PoolProperties poolProperties = new PoolProperties();
        poolProperties.setDriverClassName(environment.getProperty("db.driverClassName"));
        poolProperties.setUrl(environment.getProperty("db.url"));           
        poolProperties.setUsername(environment.getProperty("db.username"));
        poolProperties.setPassword(environment.getProperty("db.password"));

        return new org.apache.tomcat.jdbc.pool.DataSource(poolProperties);
    }

}

Answer 1

The Environment is a combination of profiles and properties.

A profile is a named, logical group of bean definitions that can be active or inactive based on your environment. Beans may be assigned to a profile whether defined in XML or via annotations. For ex. you may have one profile for development mode and another for production mode. You can look up the docs for @Profile here to see more details about it.

To quote the Environment docs:

The role of the Environment object with relation to profiles is in determining which profiles (if any) are currently active, and which profiles (if any) should be active by default.

Unless you need to access that information, you should stick to using the placeholder notation with ${..} format and the @Value annotations. Again, to quote the docs:

In most cases, however, application-level beans should not need to interact with the Environment directly but instead may have to have ${...} property values replaced by a property placeholder configurer such as PropertySourcesPlaceholderConfigurer, which itself is EnvironmentAware and as of Spring 3.1 is registered by default when using <context:property-placeholder/>.

So, to summarize:

1. With the Environement object, you can access the information related to profiles. You can't do that with @Value
2. Unless you need the info related to profiles (and you probably shouldn't), you should stick to the @Value annotations.