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法律研究JDBC中的ResultSet保持性是什么？
ResultSet保持性决定了当使用Connection接口的commit()方法提交事务（包含所述游标/ResultSet对象）时，ResultSet对象（游标）是否应该关闭或保持打开状态。
您可以使用Connection接口的setHoldability()方法设置ResultSet保持性。
con.setHoldability(ResultSet.CLOSE_CURSORS_AT_COMMIT);
ResultSet接口提供两个值来指定ResultSet的保持性，即CLOSE_CURSORS_AT_COMMIT和HOLD_CURSORS_OVER_COMMIT。
让我们使用下面所示的CREATE语句在MySQL数据库中创建一个名为MyPlayers的表：
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
如果将ResultSet对象的保持性设置为该值。每当您使用Connection接口的commit()方法提交/保存事务时，在当前事务中创建的（已打开的）ResultSet对象将被关闭。
下面的JDBC程序将保持性值设置为CLOSE_CURSORS_AT_COMMIT，通过禁用自动提交启动事务，将名为MyPlayers的表的內容检索到ResultSet对象，将新行插入到ResultSet（以及表中），并提交事务。
提交事务后，您可以使用isClosed()方法验证在事务期间检索到的ResultSet对象是关闭的还是保持打开状态。
如果您这样做，因为我们已将ResultSet保持性设置为**CLOSE_CURSORS_AT_COMMIT**，您会发现事务保存/提交后，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 {
//Registering the Driver
DriverManager.registerDriver(new com.mysql.jdbc.Driver());
//Getting the connection
String url = "jdbc:mysql://127.0.0.1/mydatabase";
Connection con = DriverManager.getConnection(url, "root", "password");
System.out.println("Connection established......");
//Setting the auto commit false
con.setAutoCommit(false);
//Setting the holdability to CLOSE_CURSORS_AT_COMMIT
con.setHoldability(ResultSet.CLOSE_CURSORS_AT_COMMIT);
//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");
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("");
}
//Inserting a new row
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();
//Committing the transaction
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
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
如果将ResultSet对象的保持性设置为该值。每当您使用Connection接口的commit()方法提交/保存事务时，在当前事务中创建的（已打开的）ResultSet对象将保持打开状态。
下面的JDBC程序将保持性值设置为HOLD_CURSORS_OVER_COMMIT，通过禁用自动提交启动事务，将名为MyPlayers的表的內容检索到ResultSet对象，将新行插入到ResultSet（以及表中），并提交事务。
提交事务后，您可以使用**isClosed()**方法验证在事务期间检索到的ResultSet对象是关闭的还是保持打开状态。
如果您这样做，因为我们已将ResultSet保持性设置为**HOLD_CURSORS_OVER_COMMIT**，您会发现事务保存/完成 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 {
//Registering the Driver
DriverManager.registerDriver(new com.mysql.jdbc.Driver());
//Getting the connection
String url = "jdbc:mysql://127.0.0.1/mydatabase";
Connection con = DriverManager.getConnection(url, "root", "password");
System.out.println("Connection established......");
//Setting the auto commit false
con.setAutoCommit(false);
//Setting the holdability to HOLD_CURSORS_OVER_COMMIT
con.setHoldability(ResultSet.HOLD_CURSORS_OVER_COMMIT);
//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");
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("");
}
//Inserting a new row
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();
//Committing the transaction
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
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
更新于：2019年7月30日
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