JDBC - Aggiornamento di un esempio di set di risultati

Di seguito è riportato l'esempio, che utilizza l'estensione ResultSet.CONCUR_UPDATABLE e ResultSet.TYPE_SCROLL_INSENSITIVEdescritto nel tutorial Set di risultati. Questo esempio spiegherebbe le operazioni INSERT, UPDATE e DELETE su una tabella.

Va notato che le tabelle su cui stai lavorando dovrebbero avere la chiave primaria impostata correttamente.

Questo codice di esempio è stato scritto in base all'ambiente e alla configurazione del database eseguita nei capitoli precedenti.

Copia e incolla il seguente esempio in JDBCExample.java, compila ed esegui come segue:

//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;
   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 to create statment with
      // required arguments for RS example.
      System.out.println("Creating statement...");
      Statement stmt = conn.createStatement(
                           ResultSet.TYPE_SCROLL_INSENSITIVE,
                           ResultSet.CONCUR_UPDATABLE);
     //STEP 5: Execute a query
      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 6: Loop through result set and add 5 in age
      //Move to BFR postion so while-loop works properly
      rs.beforeFirst();
      //STEP 7: Extract data from result set
      while(rs.next()){
         //Retrieve by column name
         int newAge = rs.getInt("age") + 5;
         rs.updateDouble( "age", newAge );
         rs.updateRow();
      }
      System.out.println("List result set showing new ages...");
      printRs(rs);
      // Insert a record into the table.
      //Move to insert row and add column data with updateXXX()
      System.out.println("Inserting a new record...");
      rs.moveToInsertRow();
      rs.updateInt("id",104);
      rs.updateString("first","John");
      rs.updateString("last","Paul");
      rs.updateInt("age",40);
      //Commit row
      rs.insertRow();

      System.out.println("List result set showing new set...");
      printRs(rs);
      
      // Delete second record from the table.
      // Set position to second record first
      rs.absolute( 2 );
      System.out.println("List the record before deleting...");
      //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);

     //Delete row
      rs.deleteRow();
      System.out.println("List result set after \
                                 deleting one records...");
      printRs(rs);

      //STEP 8: Clean-up environment
      rs.close();
      stmt.close();
      conn.close();
   }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(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

Ora compiliamo l'esempio sopra come segue:

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

Quando corri JDBCExample, produce il seguente risultato:

C:\>java JDBCExample
Connecting to database...
Creating statement...
List result set for reference....
ID: 100, Age: 33, First: Zara, Last: Ali
ID: 101, Age: 40, First: Mahnaz, Last: Fatma
ID: 102, Age: 50, First: Zaid, Last: Khan
ID: 103, Age: 45, First: Sumit, Last: Mittal

List result set showing new ages...
ID: 100, Age: 38, First: Zara, Last: Ali
ID: 101, Age: 45, First: Mahnaz, Last: Fatma
ID: 102, Age: 55, First: Zaid, Last: Khan
ID: 103, Age: 50, First: Sumit, Last: Mittal

Inserting a new record...
List result set showing new set...
ID: 100, Age: 38, First: Zara, Last: Ali
ID: 101, Age: 45, First: Mahnaz, Last: Fatma
ID: 102, Age: 55, First: Zaid, Last: Khan
ID: 103, Age: 50, First: Sumit, Last: Mittal
ID: 104, Age: 40, First: John, Last: Paul

List the record before deleting...
ID: 101, Age: 45, First: Mahnaz, Last: Fatma
List result set after deleting one records...
ID: 100, Age: 38, First: Zara, Last: Ali
ID: 102, Age: 55, First: Zaid, Last: Khan
ID: 103, Age: 50, First: Sumit, Last: Mittal
ID: 104, Age: 40, First: John, Last: Paul

Goodbye!
C:\>