connessione a un database

[deleted_2024.08.22]

Salve, vorrei sapere come effettuare una connessione a un database.

Il problema e che non riesco a connettermi al driver(non riesco a individuare il mio driver), caricare e ottenere una connessione.

Mi potete dire per piacere come si effettuano queste operazioni? Grazie mille

[Jamie04]

http://docs.oracle.com/javase/tutori...onnecting.html

[deleted_2024.08.22]

package database;
import java.util.*;
import java.sql.*;

/**
 *
 * @author francesco
 */
public class Database {
// JDBC driver name and database URL
   static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";  
   static final String DB_URL = "jdbc:mysql://localhost:3306/";

   //  Database credentials
   static final String USER = "username";
   static final String PASS = "password";
    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        // TODO code application logic here
        
        
    Connection conn = null;
   Statement stmt = null;
   try{
      //STEP 2: Register JDBC driver
      Class.forName("com.mysql.jdbc.Driver");

      //STEP 3: Open a connection
      System.out.println("Connecting to database...");
      conn = DriverManager.getConnection(DB_URL, USER, PASS);

      //STEP 4: Execute a query
      System.out.println("Creating database...");
      stmt = conn.createStatement();
      
      String sql = "CREATE DATABASE STUDENTS";
      stmt.executeUpdate(sql);
      System.out.println("Database created successfully...");
   }catch(SQLException se){
      //Handle errors for JDBC
      se.printStackTrace();
   }catch(Exception e){
      //Handle errors for Class.forName
      e.printStackTrace();
   }finally{
      //finally block used to close resources
      try{
         if(stmt!=null)
            stmt.close();
      }catch(SQLException se2){
      }// nothing we can do
      try{
         if(conn!=null)
            conn.close();
      }catch(SQLException se){
         se.printStackTrace();
      }//end finally try
   }//end try
   System.out.println("Goodbye!");
}//end main
}//end JDBCExample

Ecco i log degli errori:

java.lang.ClassNotFoundException: com.mysql.jdbc.Driver
Goodbye!
    at java.net.URLClassLoader$1.run(URLClassLoader.java:366)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:425)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:358)
    at java.lang.Class.forName0(Native Method)
    at java.lang.Class.forName(Class.java:190)
    at database.Database.main(Database.java:34)

Qualè il motivo che non carica il driver?

[Jamie04]

che non lo trova...
hai letto qui?
http://docs.oracle.com/javase/tutori...ted.html#step3

[deleted_2024.08.22]

che non lo trova...
hai letto qui?
http://docs.oracle.com/javase/tutori...ted.html#step3

Devo installare solamente il Connector/J? Non capisco

[deleted_2024.08.22]

Devo installare solamente il Connector/J? Non capisco

package database;
import java.util.*;
import java.sql.*;

/**
 *
 * @author francesco
 */
public class Database {
// JDBC driver name and database URL
   static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";  
   static final String DB_URL = "jdbc:mysql://localhost:3306/";

   //  Database credentials
   static final String USER = "username";
   static final String PASS = "password";
    /**
     * @param args the command line arguments
     */
    public static void main(String[] argc)throws SQLException,ClassNotFoundException  {
        // TODO code application logic here
        
        
    Connection conn = null;
   Statement stmt = null;
   try{
      //STEP 2: Register JDBC driver
      Class.forName("com.mysql.jdbc.Driver");

      //STEP 3: Open a connection
      System.out.println("Connecting to database...");
      conn = DriverManager.getConnection(DB_URL, USER, PASS);

      //STEP 4: Execute a query
      System.out.println("Creating database...");
      stmt = conn.createStatement();
      
      String sql = "CREATE DATABASE STUDENTS";
      stmt.executeUpdate(sql);
      System.out.println("Database created successfully...");
   }catch(SQLException se){
      //Handle errors for JDBC
      se.printStackTrace();
   }catch(Exception e){
      //Handle errors for Class.forName
      e.printStackTrace();
   }finally{
      //finally block used to close resources
      try{
         if(stmt!=null)
            stmt.close();
      }catch(SQLException se2){
      }// nothing we can do
      try{
         if(conn!=null)
            conn.close();
      }catch(SQLException se){
         se.printStackTrace();
      }//end finally try
   }//end try
   System.out.println("Goodbye!");
}//end main
}//end JDBCExample

;

Report degli errori

run:
java.lang.ClassNotFoundException: com.mysql.jdbc.Driver
Goodbye!
    at java.net.URLClassLoader$1.run(URLClassLoader.java:366)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:425)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:358)
    at java.lang.Class.forName0(Native Method)
    at java.lang.Class.forName(Class.java:190)
    at database.Database.main(Database.java:34)
BUILD SUCCESSFUL (total time: 0 seconds)

Come mai "com.mysql.jdbc.Driver" è sbagliato? Non capisco

[deleted_2024.08.22]

che non lo trova...
hai letto qui?
http://docs.oracle.com/javase/tutori...ted.html#step3

Ho installato il pacchetto Connector/J. ma da lo stesso errore

[Jamie04]

Ho installato il pacchetto Connector/J. ma da lo stesso errore

come lo hai installato?
questo è il mio codice, e funziona

// classi per database
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.ResultSet;
import java.sql.Statement;
import java.sql.DatabaseMetaData;
// classi per leggere file
import java.io.FileInputStream;
import java.io.IOException;
import java.io.FileNotFoundException;
// classe per leggere file chiave/valore
import java.util.Properties;

/**
 * Classe per connettersi a database mysql. Non e' necessario che il database sia 
 * esistente. I parametri per l'accesso devono essere in un file di nome properties.txt
 * nel formato chiave/valore. Si suppone che mysqld sia attivo e funzionante.
 *
 */
public class DBConnection {

    private static Connection connection;
    private static String driver;
    private static String url;
    private static String admin;
    private static String adm_passwd;
    private static String fileName = "properties.txt";
    private static Statement st = null;
    private static ResultSet rs = null;

    /**
     * Inizializzatore. Carica e legge il file che contiene proprieta' relative
     * a driver, url, admin, adminpasswd, e carica il driver del database con
     * metodo statico forName della classe Class che rappresenta classi ed
     * interfacce in una applicazione Java. Vengono lanciate eccezioni
     * IOException, FileNotFoundException, ClassNotFoundException
     *
     * @param fileName il nome del file che contiene proprieta' relative a
     * driver, url, admin, adminpasswd
     * @throws java.io.IOException
     * @throws java.io.FileNotFoundException
     * @throws java.lang.ClassNotFoundException
     */
    public static void init(String fileName)
            throws IOException, FileNotFoundException, ClassNotFoundException {
// predispone lettura da file con chiave/valore
        Properties properties = new Properties();
// definisce input stream da file
        FileInputStream fileInputStream = new FileInputStream(fileName);
// associa input stream a istanza Properties
        properties.load(fileInputStream);
// associa a stringhe i valori ottenuti dal file
        driver = properties.getProperty("driver");
        url = properties.getProperty("url");
        admin = properties.getProperty("admin");
        adm_passwd = properties.getProperty("admin_passwd");
        Class.forName(driver); // carica il driver in memoria
    }

    /**
     * (DriverManager) Stabilisce connessione alla base di dati mysql
     *
     * @return
     * @throws java.sql.SQLException
     */
    public static Connection getConnection() throws SQLException {
        return connection = DriverManager.getConnection(url, admin, adm_passwd);
    }

    /**
     * Crea il database e le tabelle se non esistenti
     */
    
    public static void createDb() throws SQLException {
        
        st = connection.createStatement();
        int result=st.executeUpdate("CREATE DATABASE IF NOT EXISTS TableManager");
        connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/TableManager", admin, adm_passwd);
        st = connection.createStatement();

(altre istruzioni di creazione tabelle)
       
    }
    
    /**
     * Chiude la connessione alla base di dati mysql
     */
    public static void closeConnection() throws SQLException {
        connection.close();
    }
}

[schumy2000]

Devi caricare il Jar del connector nel progetto come libreria aggiuntiva altrimenti non ti funzionerà.

[deleted_2024.08.22]

Devi caricare il Jar del connector nel progetto come libreria aggiuntiva altrimenti non ti funzionerà.

Dopo aver inserito il jar connector ora mi risultano i seguenti errori :

run:
Connecting to database...
Creating database...
com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: Access denied for user ''@'localhost' to database 'students'
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)
Goodbye!
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:526)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
    at com.mysql.jdbc.Util.getInstance(Util.java:386)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1054)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:4237)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:4169)
    at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2617)
    at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2778)
    at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2828)
    at com.mysql.jdbc.StatementImpl.executeUpdate(StatementImpl.java:1842)
    at com.mysql.jdbc.StatementImpl.executeUpdate(StatementImpl.java:1764)
    at database.Database.main(Database.java:44)
BUILD SUCCESSFUL (total time: 0 seconds)

package database;
import java.util.*;
import java.sql.*;

/**
 *
 * @author francesco
 */
public class Database {
// JDBC driver name and database URL
   static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";  
   static final String DB_URL = "jdbc:mysql://localhost:3306/";

   //  Database credentials
   static final String USER = "username";
    /**
     * @param args the command line arguments
     */
    public static void main(String[] argv)throws SQLException,  ClassNotFoundException  {
        // TODO code application logic here
        
        
    Connection conn = null;
   Statement stmt = null;
   try{
      //STEP 2: Register JDBC driver
      Class.forName("com.mysql.jdbc.Driver");

      //STEP 3: Open a connection
      System.out.println("Connecting to database...");
      conn = DriverManager.getConnection(DB_URL, USER,"");

      //STEP 4: Execute a query
      System.out.println("Creating database...");
      stmt = conn.createStatement();
      
      String sql = "CREATE DATABASE STUDENTS";
      stmt.executeUpdate(sql);
      System.out.println("Database created successfully...");
   }catch(SQLException se){
      //Handle errors for JDBC
      se.printStackTrace();
   }catch(Exception e){
      //Handle errors for Class.forName
      e.printStackTrace();
   }finally{
      //finally block used to close resources
      try{
         if(stmt!=null)
            stmt.close();
      }catch(SQLException se2){
      }// nothing we can do
      try{
         if(conn!=null)
            conn.close();
      }catch(SQLException se){
         se.printStackTrace();
      }//end finally try
   }//end try
   System.out.println("Goodbye!");
}//end main
}//end JDBCExample