JDBC - Exemple de validation et de restauration

Voici l'exemple, qui utilise commit et rollback décrit dans le didacticiel sur les transactions.

Cet exemple de code a été écrit en fonction de l'environnement et de la configuration de la base de données effectuée dans les chapitres précédents.

Copiez et collez l'exemple suivant dans JDBCExample.java, compilez et exécutez comme suit -

//STEP 1. Import required packages
import java.sql.*;

public class JDBCExample {
   // JDBC driver name and database URL
   static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";  
   static final String DB_URL = "jdbc:mysql://localhost/EMP";

   //  Database credentials
   static final String USER = "username";
   static final String PASS = "password";
   
 public static void main(String[] args) {
   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: Set auto commit as false.
      conn.setAutoCommit(false);

      //STEP 5: Execute a query to create statment with
      // required arguments for RS example.
      System.out.println("Creating statement...");
      stmt = conn.createStatement(
                           ResultSet.TYPE_SCROLL_INSENSITIVE,
                           ResultSet.CONCUR_UPDATABLE);
     
      //STEP 6: INSERT a row into Employees table
      System.out.println("Inserting one row....");
      String SQL = "INSERT INTO Employees " +
                    "VALUES (106, 20, 'Rita', 'Tez')";
      stmt.executeUpdate(SQL);  

      //STEP 7: INSERT one more row into Employees table
      SQL = "INSERT INTO Employees " +
                    "VALUES (107, 22, 'Sita', 'Singh')";
      stmt.executeUpdate(SQL);

      //STEP 8: Commit data here.
      System.out.println("Commiting data here....");
      conn.commit();
	  
	  //STEP 9: Now list all the available records.
      String sql = "SELECT id, first, last, age FROM Employees";
      ResultSet rs = stmt.executeQuery(sql);
      System.out.println("List result set for reference....");
      printRs(rs);

      //STEP 10: Clean-up environment
      rs.close();
      stmt.close();
      conn.close();
   }catch(SQLException se){
      //Handle errors for JDBC
      se.printStackTrace();
      // If there is an error then rollback the changes.
      System.out.println("Rolling back data here....");
	  try{
		 if(conn!=null)
            conn.rollback();
      }catch(SQLException se2){
         se2.printStackTrace();
      }//end try

   }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

   public static void printRs(ResultSet rs) throws SQLException{
      //Ensure we start with first row
      rs.beforeFirst();
      while(rs.next()){
         //Retrieve by column name
         int id  = rs.getInt("id");
         int age = rs.getInt("age");
         String first = rs.getString("first");
         String last = rs.getString("last");

         //Display values
         System.out.print("ID: " + id);
         System.out.print(", Age: " + age);
         System.out.print(", First: " + first);
         System.out.println(", Last: " + last);
     }
     System.out.println();
   }//end printRs()
}//end JDBCExample

Maintenant, compilons l'exemple ci-dessus comme suit -

C:\>javac JDBCExample.java
C:\>

Quand tu cours JDBCExample, il produit le résultat suivant -

C:\>java JDBCExample
Connecting to database...
Creating statement...
Inserting one row....
Commiting data here....
List result set for reference....
ID: 100, Age: 18, First: Zara, Last: Ali
ID: 101, Age: 25, First: Mahnaz, Last: Fatma
ID: 102, Age: 30, First: Zaid, Last: Khan
ID: 103, Age: 28, First: Sumit, Last: Mittal
ID: 106, Age: 20, First: Rita, Last: Tez
ID: 107, Age: 22, First: Sita, Last: Singh
Goodbye!
C:\>