JDBC 驱动程序和终端类路径

Question

I'm trying to connect to a sql database made through mysql_workbench on a linux machine. I currently code through terminal using text editors because that's what I feel comfortable in.

My DatabaseConnection class has the following code, mostly with System.out.println 's to try and find the problem cause:

final String JDBC_DRIVER = "com.mysql.jdbc.Driver";
final String DB_URL = "jdbc:mysql://localhost:3306/mydb";

final String user = "root";
final String pass = "pass";

Connection connection;
Statement statement;

public DatabaseConnection(){

}

public void connect(){
    System.out.println("Entering method");
    try {
        System.out.println("Attempting to load driver");
        Class.forName(JDBC_DRIVER); 
        System.out.println("Driver Loaded");        
        connection = DriverManager.getConnection(DB_URL, user, pass);
        System.out.println("Connection established");
        statement = connection.createStatement();
        System.out.println(" statement made");
        ResultSet resultSet = statement.executeQuery("show databases");
        System.out.println("statement executed");

        while(resultSet.next()){
            System.out.println(resultSet.next());
        }
        System.out.println("finished printing result set");

        statement.close();
    } catch(ClassNotFoundException ex) {
        System.out.println("Error: unable to load driver class!");
        System.exit(1);
    } catch (SQLException sqle) {
        System.out.println("Connection Error");         
        sqle.getErrorCode();
    }

}
}

I also have a Test class to test this:

class Test {

    public static void main(String[] args){
        DatabaseConnection connection = new DatabaseConnection();
        connection.connect();
    }
}

Currently when running it in terminal my commands are:

javac -cp .:/lib/mysql-connector-java-5.1.38-bin.jar Test.java

(In my top folder containing the .java files, I have a lib subfolder containing my jdbc driver)

That compiles fine. Next I run it using

java -cp .:/lib/mysql-connector-java-5.1.38-bin.jar Test

And I get the following error:

java -cp .:/lib/mysql-connector-java-5.1.38-bin.jar Test
Entering method
Attempting to load driver
Error: unable to load driver class!

So it looks to be it isn't loading the driver in the Class.forName() method and is failing. Could somebody possibly help with explaining why and possible solutions?

In mysql_workbench, I think the database is up and running since I am able to query it in the workbench query command line to show the databases and tables, which are currently empty.

Answer 1

Java was unable to find the JAR file for the MySQL JDBC driver because the -cp argument in

java -cp .:/lib/mysql-connector-java-5.1.38-bin.jar Test

specifies two (colon-separated) locations:

1. .
2. /lib/mysql-connector-java-5.1.38-bin.jar

The second location is interpreted as an absolute path . To have it interpreted as a relative path it should start with a period ( . ), ie,

java -cp .:./lib/mysql-connector-java-5.1.38-bin.jar Test