JDBC - 設定儲存點示例

以下是示例，它使用了事務教程中描述的 setSavepoint 和 rollback 方法。

此示例程式碼是基於前面章節中完成的環境和資料庫設定編寫的。

使用 SavePoint 回滾到之前的穩定更改示例

在這個示例中，我們有六個靜態字串，包含資料庫連線 URL、使用者名稱、密碼、SELECT 查詢和兩個 DELETE 查詢。DELETE 查詢用於刪除 Employees 表中 ID 為 8 和 9 的兩條記錄。現在，使用 DriverManager.getConnection() 方法，我們準備了一個數據庫連線。使用 setAutoCommit(false)，我們將自動提交設定為 false，預設為 true。連線準備就緒後，我們使用 connection.createStatement() 方法建立了一個 Statement 物件。在建立 Statement 物件時，我們使用了 ResultSet 型別 TYPE_SCROLL_INSENSITIVE 和 CONCUR_READ_ONLY。

使用 setSavepoint() 方法，我們設定了一個儲存點，然後刪除了 ID 為 8 的記錄。下一步，使用回滾到之前的儲存點來恢復更改。這將恢復刪除行的更改。然後，我們刪除了 ID 為 9 的記錄，並使用 printResultSet() 方法列印記錄，該方法列印結果集的所有記錄。

將以下示例複製並貼上到 JDBCExample.java 中，編譯並執行如下：

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Savepoint;
import java.sql.Statement;

public class JDBCExample {
   static final String DB_URL = "jdbc:mysql:///TUTORIALSPOINT";
   static final String USER = "guest";
   static final String PASS = "guest123";
   static final String QUERY = "SELECT id, first, last, age FROM Employees";
   static final String DELETE_QUERY = "DELETE FROM Employees WHERE ID = 8";
   static final String DELETE_QUERY_1 = "DELETE FROM Employees WHERE ID = 9";

   public static void printResultSet(ResultSet rs) throws SQLException{
      // Ensure we start with first row
      rs.beforeFirst();
      while(rs.next()){
         // Display values
         System.out.print("ID: " + rs.getInt("id"));
         System.out.print(", Age: " + rs.getInt("age"));
         System.out.print(", First: " + rs.getString("first"));
         System.out.println(", Last: " + rs.getString("last"));
      }
      System.out.println();
   }

   public static void main(String[] args) {
      // Open a connection
      try(Connection conn = DriverManager.getConnection(DB_URL, USER, PASS);
         Statement stmt = conn.createStatement(
            ResultSet.TYPE_SCROLL_INSENSITIVE,
            ResultSet.CONCUR_UPDATABLE);				
      ) {		

         conn.setAutoCommit(false);
         ResultSet rs = stmt.executeQuery(QUERY);
         System.out.println("List result set for reference....");
         printResultSet(rs);

         // delete row having ID = 8
         // But save point before doing so.
         Savepoint savepoint1 = conn.setSavepoint("ROWS_DELETED_1");
         System.out.println("Deleting row....");
         stmt.executeUpdate(DELETE_QUERY);  
         // Rollback the changes after save point 1.
         conn.rollback(savepoint1);

         // delete rows having ID = 9
         // But save point before doing so.
         conn.setSavepoint("ROWS_DELETED_2");
         System.out.println("Deleting row....");

         stmt.executeUpdate(DELETE_QUERY_1);  

         rs = stmt.executeQuery(QUERY);
         System.out.println("List result set for reference....");
         printResultSet(rs);

         // Clean-up environment
         rs.close();

      } catch (SQLException e) {
         e.printStackTrace();
      } 
   }
}

輸出

現在，讓我們編譯上面的示例，如下所示：

C:\>javac JDBCExample.java
C:\>

執行 JDBCExample 時，將產生以下結果：

C:\>java JDBCExample
List result set for reference....
ID: 1, Age: 23, First: Zara, Last: Ali
ID: 2, Age: 30, First: Mahnaz, Last: Fatma
ID: 3, Age: 35, First: Zaid, Last: Khan
ID: 4, Age: 33, First: Sumit, Last: Mittal
ID: 5, Age: 40, First: John, Last: Paul
ID: 7, Age: 20, First: Sita, Last: Singh
ID: 8, Age: 20, First: Rita, Last: Tez
ID: 9, Age: 20, First: Sita, Last: Singh

Deleting row....
Deleting row....
List result set for reference....
ID: 1, Age: 23, First: Zara, Last: Ali
ID: 2, Age: 30, First: Mahnaz, Last: Fatma
ID: 3, Age: 35, First: Zaid, Last: Khan
ID: 4, Age: 33, First: Sumit, Last: Mittal
ID: 5, Age: 40, First: John, Last: Paul
ID: 7, Age: 20, First: Sita, Last: Singh
ID: 8, Age: 20, First: Rita, Last: Tez
C:\>

使用 SavePoint 回滾到之前的更改示例

在這個示例中，我們有六個靜態字串，包含資料庫連線 URL、使用者名稱、密碼、SELECT 查詢和兩個 DELETE 查詢。DELETE 查詢用於刪除 Employees 表中 ID 為 8 的記錄。現在，使用 DriverManager.getConnection() 方法，我們準備了一個數據庫連線。使用 setAutoCommit(false)，我們將自動提交設定為 false，預設為 true。連線準備就緒後，我們使用 connection.createStatement() 方法建立了一個 Statement 物件。在建立 Statement 物件時，我們使用了 ResultSet 型別 TYPE_SCROLL_INSENSITIVE 和 CONCUR_READ_ONLY。

使用 setSavepoint() 方法，我們設定了一個儲存點，然後刪除了 ID 為 8 的記錄。下一步，使用回滾到之前的儲存點來恢復更改。這將恢復刪除行的更改。然後，使用 printResultSet() 方法列印記錄，該方法列印結果集的所有記錄。

將以下示例複製並貼上到 JDBCExample.java 中，編譯並執行如下：

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Savepoint;
import java.sql.Statement;

public class JDBCExample {
   static final String DB_URL = "jdbc:mysql:///TUTORIALSPOINT";
   static final String USER = "guest";
   static final String PASS = "guest123";
   static final String QUERY = "SELECT id, first, last, age FROM Employees";
   static final String DELETE_QUERY = "DELETE FROM Employees WHERE ID = 8";

   public static void printResultSet(ResultSet rs) throws SQLException{
      // Ensure we start with first row
      rs.beforeFirst();
      while(rs.next()){
         // Display values
         System.out.print("ID: " + rs.getInt("id"));
         System.out.print(", Age: " + rs.getInt("age"));
         System.out.print(", First: " + rs.getString("first"));
         System.out.println(", Last: " + rs.getString("last"));
      }
      System.out.println();
   }

   public static void main(String[] args) {
      // Open a connection
      try(Connection conn = DriverManager.getConnection(DB_URL, USER, PASS);
         Statement stmt = conn.createStatement(
            ResultSet.TYPE_SCROLL_INSENSITIVE,
            ResultSet.CONCUR_UPDATABLE);				
      ) {		

         conn.setAutoCommit(false);

         // Create a savepoint object before executing the 
         // deleteQuery
         Savepoint beforeDeleteSavepoint = conn.setSavepoint();
         stmt.executeUpdate(DELETE_QUERY);  
		 
		 System.out.println("Table EMPLOYEES after executing deleteQuery");
		 ResultSet rs = stmt.executeQuery(QUERY);
		 printResultSet(rs);
         
		 // Rollback the changes after delete save point.
         conn.rollback(beforeDeleteSavepoint);
         
         System.out.println("Table Employees after rollback");
         rs = stmt.executeQuery(QUERY);
         printResultSet(rs);

         // Clean-up environment
         rs.close();

      } catch (SQLException e) {
         e.printStackTrace();
      } 
   }
}

輸出

現在，讓我們編譯上面的示例，如下所示：

C:\>javac JDBCExample.java
C:\>

執行 JDBCExample 時，將產生以下結果：

C:\>java JDBCExample
Table EMPLOYEES after executing deleteQuery
ID: 1, Age: 18, First: Zara, Last: Ali
ID: 2, Age: 25, First: Mahnaz, Last: Fatma
ID: 3, Age: 30, First: Zaid, Last: Khan
ID: 4, Age: 28, First: Sumit, Last: Mittal
ID: 7, Age: 20, First: Rita, Last: Tez
Table Employees after rollback
ID: 1, Age: 18, First: Zara, Last: Ali
ID: 2, Age: 25, First: Mahnaz, Last: Fatma
ID: 3, Age: 30, First: Zaid, Last: Khan
ID: 4, Age: 28, First: Sumit, Last: Mittal
ID: 7, Age: 20, First: Rita, Last: Tez
ID: 8, Age: 20, First: Sita, Last: Singh

C:\>