How to connect to H2 database from Java & H2 DB

Question

I am fairly new to Eclipse & Java and currently work on a project where I need to implement my first database.

Therefore, I tried to connect Eclipse and the H2 Database. While the H2 database part works just fine by itself, I can't figure out how to connect it to Eclipse.

I created the following class and tried to do everything as stated on the website:

package srpTracking;

import java.sql.*;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
import org.h2.tools.DeleteDbFiles;

public class DatabaseConnector {

    public static void main(String... args) throws Exception {
        DeleteDbFiles.execute("~", "test", true);

        Class.forName("org.h2.Driver");
        Connection conn = DriverManager.getConnection("jdbc:h2:~/test");
        Statement stat = conn.createStatement();


        stat.execute("create table test(id int primary key, name varchar(255))");
        stat.execute("insert into test values(1, 'Hello')");
        ResultSet rs;
        rs = stat.executeQuery("select * from test");
        while (rs.next()) {
            System.out.println(rs.getString("name"));
        }
    }
        stat.close();
        conn.close();
 }

I get identifier errors for the last two lines of code, but it also doesn't connect anything.

I copied the H2.jar file into the project folder in a subfolder called lib.

Unfortunately I can't for some reason install the DTP plugin, because I am apparently missing a 'org.eclipse.core.runtime' file.

What do I need to change about my code connect Java and H2? Also, do I need to copy and H2 files into specific folders?

You are trying to shoehorn two entirely different problems into one question. Your first problem is that stat.close() and con.close() statements are outside the main method and therefore syntax errors: your code doesn't compile. The problem with the DTP plugin is unrelated and an Eclipse configuration/installation problem. Please edit your question to restrict it to only one problem, and ask a new, separate question for the other problem. — Mark Rotteveel
– Mark Rotteveel, Commented Dec 13, 2015 at 12:17

Jan · Accepted Answer · 2015-12-13 13:16:14Z

2

Consider these changes to your main. By using try-with-resource you delegate the close to the JVM - with the added benefit that even in cases of exceptions, you wouldn't need to close them as well.

Why it didn't work before? Your variables ran out of scope - you tried to close after main() had ended.

public static void main(String... args) throws Exception {
    DeleteDbFiles.execute("~", "test", true);

    Class.forName("org.h2.Driver");
    try (Connection conn = DriverManager.getConnection("jdbc:h2:~/test"); 
            Statement stat = conn.createStatement()) {
        stat.execute("create table test(id int primary key, name varchar(255))");
        stat.execute("insert into test values(1, 'Hello')");
        try (ResultSet rs = stat.executeQuery("select * from test")) {
            while (rs.next()) {
                System.out.println(rs.getString("name"));
            }
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
}

answered Dec 13, 2015 at 13:16

Jan

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2 Comments

Pieter De Bie Over a year ago

Whats the use of Class.forName? Checking if the driver exists?

Jan Over a year ago

Until Java 6 this triggered loading the Driver class initializing all static variables and code-blocks, allowing the Driver to register itself with JDBC. Nowadays it would merely trigger a more telling Exception (Class not found) instead of some obscure no driver found for JDBC URL.

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