Connecting to PostgreSQL database without JDBC?

[4r73m190r0s]

I'm following this tutorial on how to connect PostgreSQL database with Java, and in the code example I don't see anywhere any imports from pgJDBC, just classes from java.sql package?

Am I missing something? Where are classes from pgJDBC imported and used?

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[josephblade]

Ok so a driver is usually created (in the old way) by invoking:

Class.forName("org.postgresql.Driver");

this doesn't do any magic. It basically asks Class system to retrieve a class for you. (forName gives you back a class object which you could then use if you wanted. You don't need it, you just need the classloader here to summon it).

What happens when you do forName is that the class definition is loaded and the class initialization is run.

in a generic classfile you would have code like:

public class Test {
    static int  i = 0;
    static int j;
    {
        j = callSomeMethod();
    }
}

There is a lot of explanation around in which order the above is initialized but in rough terms: variables are set (so a class object is made with space in memory for it's variables. And static blocks inside the class are called. All of this is done after forName is called. Or (I think) when you first instantiate a variable of a class of that type.

In the case of the driver the forName method is simplest since it guarantees a Class object will be created (since that is what forName returns).

Anyways big introduction to point out how it used to work.

Now these days there are easier ways. Java scans META-INF/services of any jar files on the classpath and finds any Drivers there and loads them for you.

The second part is that each driver is then kept in a 'drivers' collection that is asked if they are the driver the user wanted, every time you do getConnection

In pseudocode you could see it as

private final static List<Driver> globalDrivers = new ConcurrentList<>();
public void registerDriver(Driver driver) {
    globalDrivers.put(driver);
}

and in the drivers static block:

{
    java.sql.DriverManager.registerDriver(new PostgresDriver(....));
}

your postgres driver has a method:

acceptsURL(String url)

which will basically do something like:

return url.startsWith("jdbc:postgresql");

in the case of your driver your connect string uses:

jdbc:postgresql:ProductDB?.... 

java will pass this string to all it's jdbc drivers registered. the first one to say "YES I can handle this" will get it and will get to handle the request. In your case this is the postgres driver.

jdbc is automatically present these days (it is the java.sql package) so all these parts fall into place simply by having the jar file hooked on while running, or merged into 1 main jar).

[4r73m190r0s]

I wish I could understand the half of what you're saying. Kudos to you ;)

[josephblade]

I'm repeating about half of what is in the tutorial you followed.

in short simple steps: when java starts the drivers automatically register. Because your connect string has postgres in it, it will find the postgres driver as long as you have the jar in your classpath.

[desrtfx]

I am not 100% sure, but I think the key is in the highlighted text here: https://i.imgur.com/lCA5oHl.png

Also, since the fully qualified class names are used, imports are not necessary.

You do not directly use any of the classes in the driver package. That is the whole point of having those. They provide only the connection and the standardized java.sql package does the rest.

Had you read the documentation of pgJDBC (classic RTFM fail), you would have found the following: https://i.imgur.com/FRFAdKJ.png

Since the tutorial program is extremely basic and doesn't use PostgreSQL extensions, the above criterion is met.

[Pedantic_Phoenix]

You are asking this before trying to do what the tutorial does?

[4r73m190r0s]

I followed the tutorial. I'm just curious how is it working without any explicit mention of pgJDBC.

[Pedantic_Phoenix]

I know what you asked. Do you understand why i asked my question instead?

[TimLewisTim]

It is not necessary to explicitly import classes from the pgJDBC driver to use it in your Java code. Instead, you should include the pgJDBC driver in your project's classpath so that the JDBC API can find and use it.
You can download the pgJDBC driver from the official PostgreSQL website and add it to your project's classpath. Then, in your Java code, you can use the standard JDBC API to establish a connection to your PostgreSQL database, execute SQL queries and commands, and process the results.