如何使用 Spring 从属性文件中读取

Question

I'd like to use Spring to read from a properties file retrieving a URL, a username, and a password. I've read many examples online and they all more or less look the same but I simply don't understand them.

One said example shows two similar methods using the @value annotation and another is using Environment env yet every example using the latter says to use env.getProperty() but that method doesn't seem to exist for that object? Using @value I don't understand the method called sampleService . Am I supposed to create an object class?

     @Configuration
     @PropertySource("classpath:src/main/resources/config.properties")
     public class EnvironmentConfig {

    @Value("${config.properties}")
     public static String url;

    @Value("${config.properties}")
    public static String username;

    @Value("${config.properties}")
    public static String password;

    @Bean
    public static DataSource logInSetup() {

        DriverManagerDataSource login = new DriverManagerDataSource();
        login.setUrl(url);
        login.setUsername(username);
        login.setPassword(password);

        return login;
     }

     @Bean
     public static PropertySourcesPlaceholderConfigurer placeHolderConfigurer() {

      return new PropertySourcesPlaceholderConfigurer();

I don't think the above is even remotely close. I'm sure this is more simple them I'm making it out to be.

Answer 1

If your properties file is something like:

url=...
username=...
password=...

You can write something like:

@Configuration
@PropertySource("classpath:src/main/resources/config.properties")
public class EnvironmentConfig {

  @Bean
  public DataSource logInSetup(@Value("${url}") String url, @Value("${username}") String username, @Value("${password}") String password) {

        DriverManagerDataSource login = new DriverManagerDataSource();
        login.setUrl(url);
        login.setUsername(username);
        login.setPassword(password);
        return login;
   }
}

You should remove static everywhere. Avoid using static with Spring.

And you don't need PropertySourcesPlaceholderConfigurer as a bean. that's what PropertySource annotation should do. Anyway, avoid using new with Spring either. Especially for Spring classes. If you are doing it, most likely it's a bug.

Btw, most likely the url to the config.properties is incorrect and should be just @PropertySource("classpath:config.properties") or maybe @PropertySource("classpath:/config.properties")