CODEWITHSUNDEEP
javamysqljdbc
sweet dreams
sweet dreams

Reputation: 2134

Program runs without exception but shows no table names

I have a few DB's in mysql and all of them contain some tables with a few columns. I got the code below from a stack overflow answer. The answer is at: How can I detect a SQL table's existence in Java?

The code gives the output-

Driver Loaded.
Got Connection.

Code-

import java.sql.Connection;
import java.sql.DatabaseMetaData;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;

public class Main {
  public static void main(String[] args) throws Exception {
DatabaseMetaData md = conn.getMetaData();
ResultSet rs = md.getTables(null, null, "%", null);
while (rs.next()) {
  System.out.println(rs.getString(3));
}  }

  static Connection conn;

  static Statement st;

  static {
try {
  // Step 1: Load the JDBC driver.
  System.out.println("Driver Loaded.");
  // Step 2: Establish the connection to the database.
  String url = "jdbc:mysql://localhost:3306/";

  conn = DriverManager.getConnection(url, "cowboy", "123456");
  System.out.println("Got Connection.");

  st = conn.createStatement();
} catch (Exception e) {
  System.err.println("Got an exception! ");
  e.printStackTrace();
  System.exit(0);
}
  }
}

Upvotes: 1

Views: 1877

Answers (2)

alain.janinm
alain.janinm

Reputation: 20065

This code is used to display the tables of a specific database, not all tables of all DB. You don't specify any database in your url String so there is nothing to display.

If you look carefully at the link used to answer the linked question, you can see String url = "jdbc:hsqldb:data/tutorial"; So you have to be connected to a database first.

PS : You may have to load the driver if you use driver prior to jdbc4, use : Class.forName("com.mysql.jdbc.Driver"); and be sure the driver is available in the classpath.

Upvotes: 1

moskito-x
moskito-x

Reputation: 11958

In your Code you only

System.out.println("Driver Loaded.");

That's not enough. You have to load the driver first!

 Class.forName("com.mysql.jdbc.Driver");
 System.out.println("Driver Loaded.");

I'm surprised that this works

conn = DriverManager.getConnection(url, "cowboy", "123456");

and that you come to this line of code.

System.out.println("Got Connection.");

with the following code, it will go, but you will not get a list of tables

static {
    try {
      // Step 1: Load the JDBC driver.
      Class.forName("com.mysql.jdbc.Driver");
      System.out.println("Driver Loaded.");
      // Step 2: Establish the connection to the database.
      String url = "jdbc:mysql://localhost";

      conn = DriverManager.getConnection(url,"user","passw");
      System.out.println("Got Connection.");
      ....
      }
}

set the database name correctly

static {
       try {
       // Step 1: Load the JDBC driver.
       Class.forName("com.mysql.jdbc.Driver");
       System.out.println("Driver Loaded.");
       // Step 2: Establish the connection to the database.
       String url = "jdbc:mysql://localhost/myDataBase";
       conn = DriverManager.getConnection(url,"user","passw");
       System.out.println("Got Connection.");
       ....
       }
}

and you can see a list of your myDataBase tables.

Upvotes: 2

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