错误：java.lang.ClassNotFoundException：org.postgresql.Driver

Question

I'm just trying to connect to postgres (13.0.1) from java (11.0.8) on Debian 10 and get the error below:

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

public class cli_test {
    public static void main(String[] args) {
    
        try {
            Connection connection = null;
            Class.forName("org.postgresql.Driver");
            
            connection = DriverManager.getConnection("jdbc:postgresql://localhost:5432/myproj", "postgres", "<pwd>");
            
            System.out.println("Connection established successfully");
        } catch (Exception e) {
            System.out.print("error: \n" + e.toString() + "\n" + e.getMessage());
        }
    }
}

I run these commands:

CLASSPATH=/usr/lib/jvm/java-11-openjdk-amd64/lib/postgresql-42.2.18.jar
javac -verbose cli_test.java
java cli_test

I have verified that the jar file exists in that location and is set to 755 permissions.

I get this error:

java.lang.ClassNotFoundException: org.postgresql.Driver

I have spent hours searching online and found many others with this problem. No other solutions I found have fixed it. I'm trying to do this without a java ide, just a text editor.

Answer 1

That's not a Java problem but you use bash in a wrong way. Setting CLASSPATH=.. will not make this environment variable available to java in the program call afterwards. Try

export CLASSPATH=.:/usr/lib/jvm/java-11-openjdk-amd64/lib/postgresql-42.2.18.jar
javac -verbose cli_test.java
java cli_test

or

CLASSPATH=.:/usr/lib/jvm/java-11-openjdk-amd64/lib/postgresql-42.2.18.jar java cli_test