[Java][FlightSQL] JDBC Driver fails when Looker formats the URL with ':direct=' instead of '://'

Start in flight/flight-sql/flight-sql-jdbc-driver at ArrowFlightJdbcDriver.java, then read ArrowFlightJdbcDriverTest and its URL-parsing tests. Reproduce the legacy :direct= case and verify that acceptsURL, getUrlsArgs, and connect handle the host, port, and parameters while the existing suite remains passing.

Describe the enhancement requested

I am running a customer-hosted Looker instance and trying to connect to Dremio using the
Apache Arrow Flight SQL JDBC driver (flight-sql-jdbc-driver), registered in Looker via a
custom_jdbc_config.yml entry so the native Dremio dialect can be kept:

- name: dremio
  dir_name: dremio
  module_path: org.apache.arrow.driver.jdbc.ArrowFlightJdbcDriver
  override_jdbc_url_subprotocol: arrow-flight-sql

override_jdbc_url_subprotocol only swaps the subprotocol token Looker plugs into its
existing, dialect-specific URL template for Dremio — it does not rewrite the rest of the
template. Looker's native Dremio dialect builds connection strings as:

jdbc:dremio:direct=<host>:<port>

so after the subprotocol override, Looker generates:

jdbc:arrow-flight-sql:direct=<host>:<port>

instead of the driver's expected format:

jdbc:arrow-flight-sql://<host>:<port>

Because ArrowFlightJdbcDriver parses the URL with java.net.URI.create(...) and strictly
expects the :// delimiter to separate scheme from host, it cannot extract a host from the
:direct= form, and the connection fails.

I tried a workaround by switching Looker's dialect dropdown to "Trino" (which emits the
standard :// format). While queries did run correctly over Arrow Flight, it broke the
Looker SQL Runner UI, since Looker then sends Trino-specific metadata queries to Dremio.

To use this driver properly with Looker, the native Dremio dialect needs to stay selected,
which means the driver needs to tolerate Looker's :direct= URL format.

Steps to Reproduce / Current Behavior

Passing a connection string containing :direct= to the driver:

jdbc:arrow-flight-sql:direct=<dremio-host>:<port>

fails instantly with:

Java::JavaSql::SQLException: URL must have a host. Expected format: jdbc:arrow-flight-sql://[host][:port][?param1=value&...]

Fix

Implemented and verified locally against flight/flight-sql-jdbc-core. Added a normalization
step to ArrowFlightJdbcDriver.java that rewrites the legacy :direct= delimiter to ://
before any URL parsing occurs, applied consistently at every entry point that parses the
connection string (acceptsURL, connect, getUrlsArgs):

// Some BI tools (e.g. Looker) generate connection strings using the legacy
// "jdbc:arrow-flight-sql:direct=<host>:<port>" syntax instead of the standard "://" delimiter.
// Normalize it so the URL can still be parsed as a valid URI.
private static final String LEGACY_DIRECT_DELIMITER = ":direct=";

private static String normalizeUrl(final String url) {
  if (url != null && url.contains(LEGACY_DIRECT_DELIMITER)) {
    return url.replace(LEGACY_DIRECT_DELIMITER, "://");
  }
  return url;
}

• acceptsURL(String url) now normalizes before checking the jdbc:arrow-flight-sql:// /
  jdbc:arrow-flight:// prefixes.
• connect(String url, Properties info) normalizes once up front and uses the normalized URL
  for both argument parsing (getUrlsArgs) and ArrowFlightConnection.createNewConnection.
• getUrlsArgs(String url) normalizes defensively as well, since it is @VisibleForTesting
  and may be called directly.

This is a purely additive, backward-compatible change — URLs that don't contain :direct=
are returned unmodified.

Testing / Verification

Added two regression tests to ArrowFlightJdbcDriverTest:

• testDriverUrlParsingMechanismShouldAcceptLegacyDirectDelimiter — verifies acceptsURL and
  getUrlsArgs correctly parse host/port/params from a jdbc:arrow-flight-sql:direct=... URL.
• testShouldConnectWhenProvidedWithLegacyDirectDelimiterUrl — verifies a live connection can
  be established end-to-end using the :direct= URL format against the test Flight SQL server.

Full ArrowFlightJdbcDriverTest suite: 18/18 tests passing, 0 failures, 0 errors.

Also validated end-to-end against a real customer-hosted Looker instance connecting to Dremio
with the native Dremio dialect (config above) — connection succeeded after applying the fix.

Additional deployment note (not part of this fix, but relevant to anyone testing it with Looker)

The flight-sql-jdbc-driver shaded jar is built with Java 17 bytecode by default
(maven.compiler.release=17 in the root POM), but Looker's bundled JRE is Java 11. Loading
the default build in Looker fails with:

UnsupportedClassVersionError: ... class file version 61.0, this version of the Java Runtime
only recognizes class file versions up to 55.0

To build a Looker-compatible jar, rebuild the driver and its Arrow-owned dependency closure
(arrow-format, arrow-memory-core, arrow-memory-netty(-buffer-patch), arrow-vector,
flight-core, flight-sql, flight-sql-jdbc-core, flight-sql-jdbc-driver) with:

mvn -pl format,memory/memory-core,memory/memory-netty,memory/memory-netty-buffer-patch,vector,flight/flight-core,flight/flight-sql,flight/flight-sql-jdbc-core,flight/flight-sql-jdbc-driver \
  -DskipTests -Dmaven.compiler.release=11 -Dmaven.compiler.source=11 -Dmaven.compiler.target=11 \
  clean install

(clean is required — Maven's incremental compiler otherwise skips recompilation when only
compiler flags change.) This may be worth calling out in the driver's documentation for users
deploying it to JVM-hosted BI tools that ship an older bundled runtime.