找不到合适的驱动程序（jdbc：pgsql）

Question

(using com.impossibl.postgres.api.jdbc)

I'm having issues establishing a connection to a database when I reference something from the hosts file.

It DOES seem to work with 'localhost' though.

Class.forName("com.impossibl.postgres.jdbc.PGDriver");
String url = "jdbc:pgsql://localhost:5432/db";
Connection conn = DriverManager.getConnection(url, "name", "pass");

I have this running inside of a docker container (on the same host machine as a postgres container). When I use the hosts IP address or the ip of the postgres container it works fine, but whenever I try to use the container name it gives me

java.sql.SQLException: No suitable driver found for jdbc:pgsql://postgres_container:5432/db

The container was linked to the postgres container when it was run, and the record is in the container's hosts file just as it should be.

Is this driver unable to reference the hosts file? If so, why does it work with localhost?

Answer 1

If it works with localhost, but not with a different hostname, then it sounds like a bug in that driver as it seems to be incorrectly rejecting the URL by returning null (which to DriverManager means, "this driver doesn't understand this URL") instead of accepting the URL and throwing an SQLException (which to DriverManager means, "this driver understands this URL, but something is wrong" (eg syntax error, problem connecting, etc).

If a JDBC driver accepts a specific URL format, it should be accepting it under all circumstances, from JDBC 4.2 section 9.2:

When the DriverManager is trying to establish a connection, it calls that driver's connect method and passes the driver the URL. If the Driver implementation understands the URL, it will return a Connection object or throw a SQLException if a connection cannot be maded to the database. If the Driver implementation does not understand the URL, it will return null .

Specifically looking at the code , it looks like the URL parser in pgjdbc-ng doesn't like underscores in host names and therefor returns null , which then causes null to be returned from the Driver instead of throwing an SQLException .

private static final Pattern URL_PATTERN =
    Pattern.compile("jdbc:pgsql:(?://((?:[a-zA-Z0-9\\-\\.]+|\\[[0-9a-f\\:]+\\])(?:\\:(?:\\d+))?(?:,(?:[a-zA-Z0-9\\-\\.]+|\\[[0-9a-f\\:]+\\])(?:\\:(?:\\d+))?)*)/)?((?:\\w|-|_)+)(?:[\\?\\&](.*))?");

Workaround: use a hostname without underscores, or an IP address.

To get the actual issues addressed, I suggest you create an issue on https://github.com/impossibl/pgjdbc-ng

Answer 2

This sounds to me like an environment issue related to the docker container configuration. The "docker" user classpath may be missing the driver directory or the docker container environment does not reference the directory or driver.

I would double check all the settings as listed in https://docs.docker.com/engine/examples/postgresql_service/ and run command line tests, etc. until you track it down.