I'm trying to write a simple code to communicate with the database. But it gives an error. The application.properties file contains a link to the localhost, username and password. In three lines. image exception text

Main.java

    public static void main(String[] args) throws SQLException {
        Class<Driver> driverClass = Driver.class;
        try (var connection = ConnectionManager.open()) {
            System.out.println(connection.getTransactionIsolation());
        }
    }
}

ConnectionManager.java

public final class ConnectionManager {

    private static final String PASSWORD_KEY = "db.password";
    private static final String USERNAME_KEY = "db.username";
    private static final String URL_KEY = "db.url";

    static {
        loadDriver();
    }
    private ConnectionManager() {
    }
    public static Connection open() {
        try {
            return DriverManager.getConnection(
                    PropertiesUtil.get(URL_KEY),
                    PropertiesUtil.get(USERNAME_KEY),
                    PropertiesUtil.get(PASSWORD_KEY)
            );
        } catch (SQLException e) {
            throw new RuntimeException(e);
        }
    }
    private static void loadDriver() {
        try {
            Class.forName("org.postgresql.Driver");
        } catch (ClassNotFoundException e) {
            throw new RuntimeException(e);
        }
    }
}

PropertiesUtil.java

public final class PropertiesUtil {
    private static final Properties PROPERTIES = new Properties();
    static {
        loadProperties();
    }
    private PropertiesUtil() {
    }
    public static String get(String key) {
        return PROPERTIES.getProperty(key);
    }
    private static void loadProperties() {
        try (var inputStream = PropertiesUtil.class.getClassLoader().getResourceAsStream("application.properties")) {
            PROPERTIES.load(inputStream);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
}

project

pgAdmin4

CodePudding user response：

The problem was solved by moving the application.properties file to the root directory in src. In idea, you can mark the file as "resources root" and the file seems to be in the root directory. I didn't find this in vs code.

CodePudding user response：

Learn how to understand errors. The error is clearly saying that inputStream in the line PROPERTIES.load(inputStream) is null. This is because:

PropertiesUtil.class.getClassLoader().getResourceAsStream("application.properties")

is trying to load a resource that does not exist. I think you're misunderstanding / mis-using gRAS here:

• The proper syntax is PropertiesUtil.class.getResourceAsStream("/application.properties")
• Regardless, it's a system designed for static, as in unchanging resources. A property file is presumably intended to be editable by the user. Hence it has no business being loaded like this - it's for resources you e.g. pack into the jar file, which you wouldn't do to a properties file.

There is no non-hacky/easy way to find 'the location where my jar resides', so you may not want to do that. One easy solution is to load from the user's home dir:

try (var in = Files.newInputStream(Paths.get(System.getProperty("user.home"), "application.properties"))) {
   PROPERTIES.load(in);
}