Spring 3 - JavaConfig: Loading a Properties File

This example shows how you can load a properties file using Spring Java-based configuration and then use those properties in ${...} placeholders in other beans in your configuration.

First, you need to create a PropertySourcesPlaceholderConfigurer bean as shown below:

import org.springframework.context.annotation.*;
import org.springframework.context.support.PropertySourcesPlaceholderConfigurer;

/**
 * Loads properties from a file called ${APP_ENV}.properties
 * or default.properties if APP_ENV is not set.
 */
@Configuration
@PropertySource("classpath:${APP_ENV:default}.properties")
public class PropertyPlaceholderConfig {

  @Bean
  public static PropertySourcesPlaceholderConfigurer propertySourcesPlaceholderConfigurer() {
    return new PropertySourcesPlaceholderConfigurer();
  }
}

Next, import this configuration into your main application config and use @Value to resolve the ${...} placeholders. For example, in the code below, the databaseUrl variable will be set from the db.url property in the properties file.

import javax.sql.DataSource;
import org.springframework.context.annotation.*;
import org.springframework.context.support.PropertySourcesPlaceholderConfigurer;

@Configuration
@Import(PropertyPlaceholderConfig.class)
public class AppConfig {

  @Value("${db.url}")      private String databaseUrl;
  @Value("${db.user}")     private String databaseUser;
  @Value("${db.password}") private String databasePassword;

  @Bean
  public DataSource personDataSource(){
    final DataSource ds = new org.apache.commons.dbcp.BasicDataSource();
    ds.setDriverClassName("oracle.jdbc.driver.OracleDriver");
    ds.setUrl(databaseUrl);
    ds.setUsername(databaseUser);
    ds.setPassword(databasePassword);
    return ds;
  }

  @Bean
  public PersonDao personDao() {
    return new PersonDao(personDataSource());
  }
}

Alternative approach:
Alternatively, you can load the properties file into the Spring Environment and then lookup the properties you need when creating your beans:

import javax.sql.DataSource;
import org.springframework.context.annotation.*;
import org.springframework.context.support.PropertySourcesPlaceholderConfigurer;
import org.springframework.core.env.Environment;

@Configuration
@PropertySource("classpath:${APP_ENV:default}.properties")
public class AppConfig {

  @Autowired
  private Environment env;

  @Bean
  public DataSource personDataSource() {
    final DataSource ds = new org.apache.commons.dbcp.BasicDataSource();
    ds.setDriverClassName("oracle.jdbc.driver.OracleDriver");
    ds.setUrl(env.getProperty("db.url"));
    ds.setUsername(env.getProperty("db.user"));
    ds.setPassword(env.getProperty("db.password"));
    return ds;
  }

  @Bean
  public PersonDao personDao() {
    return new PersonDao(personDataSource());
  }
}

A minor downside of this approach is that you need to autowire the Environment into all your configs which require properties from the properties file.

Related posts:
Spring 3: JavaConfig vs XML Config