詳解Java的JDBC API中事務的提交和復原_java

如果JDBC串連是在自動認可模式下，它在預設情況下，那麼每個SQL語句都是在其完成時提交到資料庫。

這可能是對簡單的應用程式，但有三個原因，你可能想關閉自動認可和管理自己的事務：

1. 為了提高效能
2. 為了保持商務程序的完整性
3. 使用分散式交易

若要控制事務，以及何時更改應用到資料庫。它把單個SQL語句或一組SQL語句作為一個邏輯單元，而且如果任何語句失敗，整個事務失敗。

若要啟用，而不是JDBC驅動程式預設使用auto-commit模式手動事務支援，使用Connection對象的的setAutoCommit()方法。如果傳遞一個布爾值false到setAutoCommit()，關閉自動認可。可以傳遞一個布爾值true將其重新開啟。

例如，如果有一個名為conn Connection對象，以下代碼來關閉自動認可：

conn.setAutoCommit(false);

提交和復原
一旦已經完成了變化，要提交更改，然後調用commit（在連線物件）方法，如下所示：

conn.commit( );

否則復原更新對資料庫所做的使用命名串連conn，使用下面的代碼：

conn.rollback( );

下面的例子示範了如何使用一個提交和復原對象：

try{  //Assume a valid connection object conn  conn.setAutoCommit(false);  Statement stmt = conn.createStatement();    String SQL = "INSERT INTO Employees " +        "VALUES (106, 20, 'Rita', 'Tez')";  stmt.executeUpdate(SQL);   //Submit a malformed SQL statement that breaks  String SQL = "INSERTED IN Employees " +        "VALUES (107, 22, 'Sita', 'Singh')";  stmt.executeUpdate(SQL);  // If there is no error.  conn.commit();}catch(SQLException se){  // If there is any error.  conn.rollback();}

在這種情況下沒有上述INSERT語句會成功，一切都將被復原。

事務提交和復原樣本
以下是使用事務提交和復原描述的例子。

基於對環境和資料庫安裝在前面的章節中做此範例程式碼已學習過。

複製過去下面的例子中JDBCExample.java，編譯並運行，如下所示：

//STEP 1. Import required packagesimport 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

現在讓我們來編譯上面的例子如下：

C:>javac JDBCExample.java

當運行JDBCExample，它會產生以下結果：

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: AliID: 101, Age: 25, First: Mahnaz, Last: FatmaID: 102, Age: 30, First: Zaid, Last: KhanID: 103, Age: 28, First: Sumit, Last: MittalID: 106, Age: 20, First: Rita, Last: TezID: 107, Age: 22, First: Sita, Last: SinghGoodbye!