There are many ways to connect to the database using Java, the most common way is through the parameters contained in the database connection URL. It provides you with the information postgres://[username]:[password]@[host]/[database name].
You can connect via JDBC using the DATABASE_URL variable or using another database URL provided by Heroku. The JDBC connection is performed through the database URL parsing and extracting the necessary parameters. The following is just a code sample to help you understand the concept:
URI connectionParams = new URI(System.getenv("DATABASE_URL")); String jdbcUrl = "jdbc:postgresql://" + connectionParams.getHost() + connectionParams.getPath(); Properties properties = new Properties(); properties.setProperty("username", connectionParams.getUserInfo().split(":")[0]); properties.setProperty("password", connectionParams.getUserInfo().split(":")[1]); Connection connection = DriverManager.getConnection(jdbcUrl, properties);