JDBC中的ResultSet可保持性是什么？

2024-04-26 18:30:04 25

ResultSet的可保持性确定使用commit()Connection接口的方法提交事务（包含游标/ResultSet对象）时是关闭还是保持ResultSet对象（光标）打开。

您可以使用setHoldability()Connection接口的方法设置ResultSet可保存性。

con.setHoldability(ResultSet.CLOSE_CURSORS_AT_COMMIT);

ResultSet接口提供两个值来指定ResultSet的可保存性，即CLOSE_CURSORS_AT_COMMIT和HOLD_CURSORS_OVER_COMMIT。

让我们使用CREATE语句在MySQL数据库中创建一个名为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)
);

现在，我们将使用INSERT语句在MyPlayers表中插入7条记录-

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');

CLOSE_CURSORS_AT_COMMIT

如果ResultSet对象的可保存性设置为此值。每当使用commit()Connection接口的方法提交/保存事务时，将关闭在当前事务中创建的ResultSet对象（已打开）。

接下来的JDBC程序将可保存性值设置为CLOSE_CURSORS_AT_COMMIT，通过禁用自动提交来启动事务，将名为MyPlayers的表的内容检索到ResultSet对象，将新行插入到ResultSet（以及表）中并提交事务。

提交事务后，可以验证使用该isClosed()方法关闭还是保持打开期间在事务期间获取的ResultSet对象。

如果您这样做了，因为我们已经将ResultSet的可保留性设置为CLOSE_CURSORS_AT_COMMIT，则可以发现在保存/提交事务后，ResultSet对象rs已关闭。

示例

import java.sql.Connection;
import java.sql.Date;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
public class ResultSetHoldability_CloseCursorsAtCommit {
   public static void main(String args[]) throws SQLException {
      //注册驱动程序
      DriverManager.registerDriver(new com.mysql.jdbc.Driver());
      //获得连接
      String url = "jdbc:mysql://localhost/mydatabase";
      Connection con = DriverManager.getConnection(url, "root", "password");
      System.out.println("Connection established......");
      //将自动提交设置为false-
      con.setAutoCommit(false);
      //将可保存性设置为CLOSE_CURSORS_AT_COMMIT-
      con.setHoldability(ResultSet.CLOSE_CURSORS_AT_COMMIT);
      //创建一个Statement对象
      Statement stmt = con.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE, ResultSet.CONCUR_UPDATABLE);
      //检索数据
      ResultSet rs = stmt.executeQuery("select * from MyPlayers");
      System.out.println("Contents of the table");
      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("");
      }
      //插入新行
      rs.moveToInsertRow();
      rs.updateInt(1, 8);
      rs.updateString(2, "Ishant");
      rs.updateString(3, "Sharma");
      rs.updateDate(4, new Date(904694400000L));
      rs.updateString(5, "Delhi");
      rs.updateString(6, "India");
      rs.insertRow();
      //提交事务
      con.commit();
      boolean bool = rs.isClosed();
      if(bool) {
         System.out.println("ResultSet object is closed");
      } else {
         System.out.println("ResultSet object is open");
      }
   }
}

输出结果

Connection established......
Contents of the table
ID: 1, First_Name: Shikhar, Last_Name: DhawanDate_Of_Birth: 1981-12-05, Place_Of_Birth: DelhiCountry: India
ID: 2, First_Name: Jonathan, Last_Name: TrottDate_Of_Birth: 1981-04-22, Place_Of_Birth: CapeTownCountry: SouthAfrica
ID: 3, First_Name: Kumara, Last_Name: SangakkaraDate_Of_Birth: 1977-10-27, Place_Of_Birth: MataleCountry: Srilanka
ID: 4, First_Name: Virat, Last_Name: KohliDate_Of_Birth: 1988-11-05, Place_Of_Birth: MumbaiCountry: India
ID: 5, First_Name: Rohit, Last_Name: SharmaDate_Of_Birth: 1987-04-30, Place_Of_Birth: NagpurCountry: India
ID: 6, First_Name: Ravindra, Last_Name: JadejaDate_Of_Birth: 1988-12-06, Place_Of_Birth: NagpurCountry: India
ID: 7, First_Name: James, Last_Name: AndersonDate_Of_Birth: 1982-06-30, Place_Of_Birth: Burnley Country: England
ResultSet object is closed

HOLD_CURSORS_OVER_COMMIT

如果ResultSet对象的可保存性设置为此值。每当使用commit()Connection接口的方法提交/保存事务时，在当前事务中创建的ResultSet对象（已打开）将保持打开状态。

接下来的JDBC程序将可保存性值设置为HOLD_CURSORS_OVER_COMMIT，通过禁用自动提交启动事务，将名为MyPlayers的表的内容检索到ResultSet对象，将新行插入ResultSet（以及表）中并提交事务。

提交事务后，可以验证在事务期间检索到的ResultSet对象是关闭还是使用isClosed()方法保持打开状态。

如果您这样做了，因为我们将ResultSet的可保留性设置为HOLD_CURSORS_OVER_COMMIT，则可以发现在保存/完成事务后ResultSet对象rs保持打开状态。

示例

import java.sql.Connection;
import java.sql.Date;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
public class ResultSetHoldability_Hold_Cursors_Over_Commit {
   public static void main(String args[]) throws SQLException {
      //注册驱动程序
      DriverManager.registerDriver(new com.mysql.jdbc.Driver());
      //获得连接
      String url = "jdbc:mysql://localhost/mydatabase";
      Connection con = DriverManager.getConnection(url, "root", "password");
      System.out.println("Connection established......");
      //将自动提交设置为false-
      con.setAutoCommit(false);
      //将可保持性设置为HOLD_CURSORS_OVER_COMMIT-
      con.setHoldability(ResultSet.HOLD_CURSORS_OVER_COMMIT);
      //创建一个Statement对象
      Statement stmt = con.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE, ResultSet.CONCUR_UPDATABLE);
      //检索数据
      ResultSet rs = stmt.executeQuery("select * from MyPlayers");
      System.out.println("Contents of the table");
      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("");
      }
      //插入新行
      rs.moveToInsertRow();
      rs.updateInt(1, 8);
      rs.updateString(2, "Ishant");
      rs.updateString(3, "Sharma");
      rs.updateDate(4, new Date(904694400000L));
      rs.updateString(5, "Delhi");
      rs.updateString(6, "India");
      rs.insertRow();
      //提交事务
      con.commit();
      boolean bool = rs.isClosed();
      if(bool) {
         System.out.println("ResultSet object is closed");
      } else {
         System.out.println("ResultSet object is open");
      }
   }
}

输出结果

Connection established......
Contents of the table
ID: 1, First_Name: Shikhar, Last_Name: DhawanDate_Of_Birth: 1981-12-05, Place_Of_Birth: DelhiCountry: India
ID: 2, First_Name: Jonathan, Last_Name: TrottDate_Of_Birth: 1981-04-22, Place_Of_Birth: CapeTownCountry: SouthAfrica
ID: 3, First_Name: Kumara, Last_Name: SangakkaraDate_Of_Birth: 1977-10-27, Place_Of_Birth: MataleCountry: Srilanka
ID: 4, First_Name: Virat, Last_Name: KohliDate_Of_Birth: 1988-11-05, Place_Of_Birth: MumbaiCountry: India
ID: 5, First_Name: Rohit, Last_Name: SharmaDate_Of_Birth: 1987-04-30, Place_Of_Birth: NagpurCountry: India
ID: 6, First_Name: Ravindra, Last_Name: JadejaDate_Of_Birth: 1988-12-06, Place_Of_Birth: NagpurCountry: India
ID: 7, First_Name: James, Last_Name: AndersonDate_Of_Birth: 1982-06-30, Place_Of_Birth: Burnley Country: England
ResultSet object is open

JDBC中的ResultSet可保持性是什么？

CLOSE_CURSORS_AT_COMMIT

示例

HOLD_CURSORS_OVER_COMMIT

示例

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