解决方案:

需要使用System.getProperty而不是System.getenv.

    String host = System.getProperty("RDS_HOSTNAME");
    String port = System.getProperty("RDS_PORT");
    String username = System.getProperty("RDS_USERNAME");
    String password = System.getProperty("RDS_PASSWORD");
    String dbname = System.getProperty("RDS_DB_NAME");

Java服务现在连接到数据库.

The Java service now connects to the database.