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| -rw-r--r-- | wiki/java/stop-using-class-dot-forname.md | 62 |
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diff --git a/wiki/java/stop-using-class-dot-forname.md b/wiki/java/stop-using-class-dot-forname.md new file mode 100644 index 0000000..8f4ead8 --- /dev/null +++ b/wiki/java/stop-using-class-dot-forname.md @@ -0,0 +1,62 @@ +# JDBC Drivers and `Class.forName()` + +The short version: stop using `Class.forName(driverClass)` to load JDBC +drivers. You don't need this, and haven't since Java 5. You arguably never +needed this. + +This pattern appears all over the internet, and it's wrong. + +## Backstory + +JDBC has more or less always provided two ways to set up `Connection` objects: + +1. Obtain them from a driver-provided `DataSource` class, which applications or + containers are expected to create for themselves. + +2. Obtain them by passing a URL to `DriverManager`. + +Most people start with the latter, since it's very straightforward to use. +However, `DriverManager` needs to be able to locate `Driver` subclasses, and +the JVM doesn't permit class enumeration at runtime. + +In the original JDBC release, `Driver` subclasses were expected to register +themselves on load, similar to + + public class ExampleDriver extends Driver { + static { + DriverManager.registerDriver(ExampleDriver.class); + } + } + +Obviously, applications _can_ force drivers to load using +`Class.forName(driverName)`, but this hasn't ever been the only way to do it. +`DriverManager` also provides [a mechanism to load a set of named classes at +startup](https://docs.oracle.com/javase/8/docs/api/java/sql/DriverManager.html), +via the `jdbc.drivers` [system property](http://docs.oracle.com/javase/tutorial/essential/environment/sysprop.html). + +## JDBC 4 Fixed That + +JDBC 4, which came out with Java 6 in the Year of our Lord _Two Thousand and +Six_, also loads drivers using the [service +provider](https://docs.oracle.com/javase/8/docs/technotes/guides/jar/jar.html#Service%20Provider) +system, which requires no intervention at all from deployers or application +developers. + +_You don't need to write any code to load a JDBC 4 driver._ + +## But What About My Database? + +You don't need to worry about it. All of the following drivers support JDBC +4-style automatic discovery: + +* PostgreSQL (since version 8.0-321, in 2007) + +* Firebird (since [version 2.2, in 2009](http://tracker.firebirdsql.org/browse/JDBC-140)) + +* [MySQL](../mysql/choose-something-else) (since [version 5.0, in 2005](http://dev.mysql.com/doc/relnotes/connector-j/en/news-5-0-0.html)) + +* H2 (since day 1, as far as I can tell) + +* Derby/JavaDB (since [version 10.2.1.6, in 2006](https://issues.apache.org/jira/browse/DERBY-930)) + +* SQL Server (version unknown, because MSDN is archaeologically hostile) |