詳解Java的JDBC API中事務的提交和回滾

詳解Java的JDBC API中事務的提交和回滾。本站提示廣大學習愛好者：（詳解Java的JDBC API中事務的提交和回滾）文章只能為提供參考，不一定能成為您想要的結果。以下是詳解Java的JDBC API中事務的提交和回滾正文

假如JDBC銜接是在主動提交形式下，它在默許情形下，那末每一個SQL語句都是在其完成時提交到數據庫。

這能夠是對簡略的運用法式，但有三個緣由，你能夠想封閉主動提交和治理本身的事務：

1. 為了進步機能
2. 為了堅持營業流程的完全性
3. 應用散布式事務

若要掌握事務，和什麼時候更改運用到數據庫。它把單個SQL語句或一組SQL語句作為一個邏輯單位，並且假如任何語句掉敗，全部事務掉敗。

若要啟用，而不是JDBC驅動法式默許應用auto-commit形式手動事務支撐，應用Connection對象的的setAutoCommit()辦法。假如傳遞一個布爾值false到setAutoCommit()，封閉主動提交。可以傳遞一個布爾值true將其從新翻開。

例如，假如有一個名為conn Connection對象，以下代碼來封閉主動提交：

conn.setAutoCommit(false);

提交和回滾
一旦曾經完成了變更，要提交更改，然後挪用commit（在銜接對象）辦法，以下所示：

conn.commit( );

不然回滾更新對數據庫所做的應用定名銜接conn，應用上面的代碼：

conn.rollback( );

上面的例子演示了若何應用一個提交和回滾對象：

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();
}

在這類情形下沒有上述INSERT語句會勝利，一切都將被回滾。

事務提交和回滾示例
以下是應用事務提交和回滾描寫的例子。

基於對情況和數據庫裝置在後面的章節中做此示例代碼已進修過。

復制曩昔上面的例子中JDBCExample.java，編譯並運轉，以下所示：

//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

如今讓我們來編譯下面的例子以下：

C:>javac JDBCExample.java

當運轉JDBCExample，它會發生以下成果：

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: 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!