国产探花免费观看_亚洲丰满少妇自慰呻吟_97日韩有码在线_资源在线日韩欧美_一区二区精品毛片,辰东完美世界有声小说,欢乐颂第一季,yy玄幻小说排行榜完本

首頁(yè) > 編程 > Java > 正文

詳解Java的JDBC API中事務(wù)的提交和回滾

2019-11-26 14:43:46
字體:
供稿:網(wǎng)友

如果JDBC連接是在自動(dòng)提交模式下,它在默認(rèn)情況下,那么每個(gè)SQL語(yǔ)句都是在其完成時(shí)提交到數(shù)據(jù)庫(kù)。

這可能是對(duì)簡(jiǎn)單的應(yīng)用程序,但有三個(gè)原因,你可能想關(guān)閉自動(dòng)提交和管理自己的事務(wù):

  1. 為了提高性能
  2. 為了保持業(yè)務(wù)流程的完整性
  3. 使用分布式事務(wù)

若要控制事務(wù),以及何時(shí)更改應(yīng)用到數(shù)據(jù)庫(kù)。它把單個(gè)SQL語(yǔ)句或一組SQL語(yǔ)句作為一個(gè)邏輯單元,而且如果任何語(yǔ)句失敗,整個(gè)事務(wù)失敗。

若要啟用,而不是JDBC驅(qū)動(dòng)程序默認(rèn)使用auto-commit模式手動(dòng)事務(wù)支持,使用Connection對(duì)象的的setAutoCommit()方法。如果傳遞一個(gè)布爾值false到setAutoCommit(),關(guān)閉自動(dòng)提交。可以傳遞一個(gè)布爾值true將其重新打開。

例如,如果有一個(gè)名為conn Connection對(duì)象,以下代碼來關(guān)閉自動(dòng)提交:

conn.setAutoCommit(false);

提交和回滾
一旦已經(jīng)完成了變化,要提交更改,然后調(diào)用commit(在連接對(duì)象)方法,如下所示:

conn.commit( );

否則回滾更新對(duì)數(shù)據(jù)庫(kù)所做的使用命名連接conn,使用下面的代碼:

conn.rollback( );

下面的例子演示了如何使用一個(gè)提交和回滾對(duì)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(yǔ)句會(huì)成功,一切都將被回滾。

事務(wù)提交和回滾示例
以下是使用事務(wù)提交和回滾描述的例子。

基于對(duì)環(huán)境和數(shù)據(jù)庫(kù)安裝在前面的章節(jié)中做此示例代碼已學(xué)習(xí)過。

復(fù)制過去下面的例子中JDBCExample.java,編譯并運(yùn)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(xiàn)在讓我們來編譯上面的例子如下:

C:>javac JDBCExample.java

當(dāng)運(yùn)行JDBCExample,它會(huì)產(chǎn)生以下結(jié)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!
發(fā)表評(píng)論 共有條評(píng)論
用戶名: 密碼:
驗(yàn)證碼: 匿名發(fā)表
主站蜘蛛池模板: 来宾市| 洞头县| 红桥区| 綦江县| 大竹县| 云霄县| 迁西县| 当阳市| 克东县| 抚松县| 凉城县| 独山县| 汉中市| 新晃| 观塘区| 合川市| 陆川县| 洛扎县| 金秀| 鲁山县| 连江县| 绥中县| 和林格尔县| 康乐县| 留坝县| 山东省| 南昌县| 运城市| 天水市| 大邑县| 青浦区| 蒙自县| 龙海市| 肃北| 辉南县| 湖口县| 望城县| 乳山市| 绥芬河市| 怀柔区| 富民县|