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)：
- 為了提高性能
- 為了保持業(yè)務(wù)流程的完整性
- 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(kāi)。
例如，如果有一個(gè)名為conn Connection對(duì)象，以下代碼來(lái)關(guān)閉自動(dòng)提交：
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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：
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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：
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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：
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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(méi)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(guò)。
復(fù)制過(guò)去下面的例子中JDBCExample.java，編譯并運(yùn)行，如下所示：
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//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(lái)編譯上面的例子如下：
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C:>javac JDBCExample.java |
當(dāng)運(yùn)行JDBCExample，它會(huì)產(chǎn)生以下結(jié)果：
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C:>java JDBCExample |
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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! |
