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法學Java Connection releaseSavepoint() 方法及示例
儲存點是事務中的一個邏輯回滾點。設定儲存點後，如果在儲存點之後發生錯誤，可以使用 **rollback()** 方法撤銷在此儲存點之前執行的操作。
可以使用 Connection 介面的 **setSavepoint()** 方法在資料庫中設定儲存點。
可以使用 **releaseSavepoint()** 方法刪除/釋放儲存點。
此方法接受一個 **Savepoint** 物件作為引數，並刪除指定的儲存點。
要釋放儲存點：
使用 DriverManager 類的 registerDriver() 方法註冊驅動程式：
//Registering the Driver DriverManager.registerDriver(new com.mysql.jdbc.Driver());
使用 DriverManager 類的 getConnection() 方法獲取連線：
//Getting the connection String url = "jdbc:mysql:///mydatabase"; Connection con = DriverManager.getConnection(url, "root", "password");
使用 **setSavepoint() 方法** 將儲存點設定為所需值，並使用 Connection 介面的 setHoldability() 方法：
Savepoint savePoint = con.setSavepoint("MysavePoint");如果不需要儲存點，請使用 **releaseSavepoint()** 方法釋放它。
con.releaseSavepoint("MysavePoint");讓我們使用 CREATE 語句在 MySQL 資料庫中建立一個名為 **MyPlayers** 的表，如下所示：
CREATE TABLE MyPlayers( ID INT, First_Name VARCHAR(255), Last_Name VARCHAR(255), Date_Of_Birth date, Place_Of_Birth VARCHAR(255), Country VARCHAR(255), PRIMARY KEY (ID) );
現在，我們將使用 INSERT 語句在 MyPlayers 表中插入 7 條記錄：
insert into MyPlayers values(1, 'Shikhar', 'Dhawan', DATE('1981-12-05'), 'Delhi', 'India');
insert into MyPlayers values(2, 'Jonathan', 'Trott', DATE('1981-04-22'), 'CapeTown', 'SouthAfrica');
insert into MyPlayers values(3, 'Kumara', 'Sangakkara', DATE('1977-10-27'), 'Matale', 'Srilanka');
insert into MyPlayers values(4, 'Virat', 'Kohli', DATE('1988-11-05'), 'Delhi', 'India');
insert into MyPlayers values(5, 'Rohit', 'Sharma', DATE('1987-04-30'), 'Nagpur', 'India');
insert into MyPlayers values(6, 'Ravindra', 'Jadeja', DATE('1988-12-06'), 'Nagpur', 'India');
insert into MyPlayers values(7, 'James', 'Anderson', DATE('1982-06-30'), 'Burnley', 'England');下面的 JDBC 程式演示了 **Connection** 介面的 releaseSavepoint() 方法。在這裡，我們在 Myplayers 表中插入了一條新記錄。設定儲存點，刪除之前插入的記錄，回滾到建立的儲存點，最後顯示錶的內容並使用 releaseSavepoint() 方法釋放建立的儲存點。
示例
import java.sql.Connection;
import java.sql.Date;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Savepoint;
import java.sql.Statement;
public class Connection_releaseSavepoint {
public static void main(String args[]) throws SQLException {
//Registering the Driver
DriverManager.registerDriver(new com.mysql.jdbc.Driver());
//Getting the connection
String url = "jdbc:mysql:///mydatabase";
Connection con = DriverManager.getConnection(url, "root", "password");
System.out.println("Connection established......");
//Setting the auto commit false
con.setAutoCommit(false);
//Creating a Statement object
Statement stmt = con.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE, ResultSet.CONCUR_UPDATABLE);
//Retrieving the data
ResultSet rs = stmt.executeQuery("select * from MyPlayers");
System.out.println("Contents of the table initially");
while(rs.next()) {
System.out.print("ID: "+rs.getString("ID")+", ");
System.out.print("First_Name: "+rs.getString("First_Name")+", ");
System.out.print("Last_Name: "+rs.getString("Last_Name")+", ");
System.out.print("Date_Of_Birth: "+rs.getString("Date_Of_Birth")+", ");
System.out.print("Place_Of_Birth: "+rs.getString("Place_Of_Birth")+", ");
System.out.print("Country: "+rs.getString("Country"));
System.out.println("");
}
PreparedStatement pstmt = con.prepareStatement("INSERT INTO MyPlayers VALUES (?, ?, ?, ?, ?, ?)");
pstmt.setInt(1, 8);
pstmt.setString(2, "Virat");
pstmt.setString(3, "Kohli");
pstmt.setDate(4, new Date(594733933000L));
pstmt.setString(5, "Delhi");
pstmt.setString(6, "India");
pstmt.executeUpdate();
//Setting the save point
Savepoint savePoint = con.setSavepoint("MysavePoint");
//Deleting the record
stmt.execute("Delete from MyPlayers where id = 8");
//Rolling back to the save point
con.rollback(savePoint);
//Contents of the table after the roll-back
System.out.println("Contents of the table");
rs = stmt.executeQuery("select * from MyPlayers");
while(rs.next()) {
System.out.print("ID: "+rs.getString("ID")+", ");
System.out.print("First_Name: "+rs.getString("First_Name")+", ");
System.out.print("Last_Name: "+rs.getString("Last_Name")+", ");
System.out.print("Date_Of_Birth: "+rs.getString("Date_Of_Birth")+", ");
System.out.print("Place_Of_Birth: "+rs.getString("Place_Of_Birth")+", ");
System.out.print("Country: "+rs.getString("Country"));
System.out.println("");
}
con.releaseSavepoint(savePoint);
System.out.println("Save point released");
}
}現在，您可以觀察到在儲存點之前建立的新記錄出現在結果中。由於我們在設定儲存點後刪除了此記錄，因此在回滾時會恢復此記錄。
輸出
Connection established...... Contents of the table initially ID: 1, First_Name: Shikhar, Last_Name: Dhawan, Date_Of_Birth: 1981-12-05, Place_Of_Birth: Delhi, Country: India ID: 2, First_Name: Jonathan, Last_Name: Trott, Date_Of_Birth: 1981-04-22, Place_Of_Birth: CapeTown, Country: SouthAfrica ID: 3, First_Name: Kumara, Last_Name: Sangakkara, Date_Of_Birth: 1977-10-27, Place_Of_Birth: Matale, Country: Srilanka ID: 4, First_Name: Virat, Last_Name: Kohli, Date_Of_Birth: 1988-11-05, Place_Of_Birth: Mumbai, Country: India ID: 5, First_Name: Rohit, Last_Name: Sharma, Date_Of_Birth: 1987-04-30, Place_Of_Birth: Nagpur, Country: India ID: 6, First_Name: Ravindra, Last_Name: Jadeja, Date_Of_Birth: 1988-12-06, Place_Of_Birth: Nagpur, Country: India ID: 7, First_Name: James, Last_Name: Anderson, Date_Of_Birth: 1982-06-30, Place_Of_Birth: Burnley , Country: England Contents of the table after rollback ID: 1, First_Name: Shikhar, Last_Name: Dhawan, Date_Of_Birth: 1981-12-05, Place_Of_Birth: Delhi, Country: India ID: 2, First_Name: Jonathan, Last_Name: Trott, Date_Of_Birth: 1981-04-22, Place_Of_Birth: CapeTown, Country: SouthAfrica ID: 3, First_Name: Kumara, Last_Name: Sangakkara, Date_Of_Birth: 1977-10-27, Place_Of_Birth: Matale, Country: Srilanka ID: 4, First_Name: Virat, Last_Name: Kohli, Date_Of_Birth: 1988-11-05, Place_Of_Birth: Mumbai, Country: India ID: 5, First_Name: Rohit, Last_Name: Sharma, Date_Of_Birth: 1987-04-30, Place_Of_Birth: Nagpur, Country: India ID: 6, First_Name: Ravindra, Last_Name: Jadeja, Date_Of_Birth: 1988-12-06, Place_Of_Birth: Nagpur, Country: India ID: 7, First_Name: James, Last_Name: Anderson, Date_Of_Birth: 1982-06-30, Place_Of_Birth: Burnley , Country: England ID: 8, First_Name: Virat, Last_Name: Kohli, Date_Of_Birth: 1988-11-05, Place_Of_Birth: Delhi, Country: India Save point released
更新於：2019-07-30
瀏覽量：337
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