Jdbc-commit-rollback

JDBC-コミットとロールバックの例

以下は、トランザクションチュートリアルで説明されている commit および rollback を使用する例です。

このサンプルコードは、前の章で行った環境とデータベースのセットアップに基づいて記述されています。

JDBCExample.javaで次の例をコピーして貼り付け、次のようにコンパイルして実行します-

//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

今、私たちは次のように上記の例をコンパイルしましょう-

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

*JDBCExample* を実行すると、次の結果が生成されます-

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:\>