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法律研究如何使用JDBC从表中检索DATALINK对象？
DATALINK对象表示一个URL值，该值引用外部资源（当前数据库/数据源之外），可以是文件、目录等。
您可以使用**PreparedStatement**接口的**getURL()**方法从SQL表中检索DATALINK对象。此方法接受一个整数，表示ResultSet中列的索引，并返回指定索引中的URL对象。
示例
让我们使用如下所示的CREATE语句在MySQL数据库中创建一个名为tutorials_data的表：
CREATE TABLE tutorials_data ( tutorial_id INT PRIMARY KEY AUTO_INCREMENT, tutorial_title VARCHAR(100), tutorial_author VARCHAR(40), submission_date date, tutorial_link VARCHAR(255) );
现在，我们将使用INSERT语句在tutorials_data表中插入5条记录：
insert into tutorials_data (tutorial_title, tutorial_author, submission_date, tutorial_link) values('Java', 'Krishna Kasyap', DATE('2019-09-01'), 'https://tutorialspoint.com/java');
insert into tutorials_data (tutorial_title, tutorial_author, submission_date, tutorial_link) values('JFreeCharts', 'Satish Kumar', DATE('2019-05-01 '), 'https://tutorialspoint.com/jfreechart');
insert into tutorials_data (tutorial_title, tutorial_author, submission_date, tutorial_link) values('Android', 'Sai Ram', DATE('2019-03-01'), 'https://tutorialspoint.com/android');
insert into tutorials_data (tutorial_title, tutorial_author, submission_date, tutorial_link) values('Cassandra', 'Pruthvi Raj', DATE('2019-04-06'), 'https://tutorialspoint.com/cassandra');
insert into tutorials_data (tutorial_title, tutorial_author, submission_date, tutorial_link) values('JavaFX', 'Sarmista sharma', DATE('2018-05-01'), 'https://tutorialspoint.com/javafx下面的JDBC程序与**MySQL**数据库建立连接，并检索tutorials_data表的内容。在这里，我们使用getURL()方法获取每一记录下tutorial_link列的URL(DATALINK)值。
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
public class RetrievingDataLinkObjects {
public static void main(String args[])throws Exception{
//Registering the Driver
DriverManager.registerDriver(new com.mysql.jdbc.Driver());
//Getting the connection
String mysqlUrl = "jdbc:mysql:///sampledatabase";
Connection con = DriverManager.getConnection(mysqlUrl, "root", "password");
System.out.println("Connection established......");
//Creating a Statement object
Statement stmt = con.createStatement();
//Query to retrieve the contents of the tutorials_data table
String query = "select * from tutorials_data";
//Executing the statement
ResultSet rs = stmt.executeQuery(query);
System.out.println("Contents of the table tutorials_data: ");
//Retrieving the contents of the table
while(rs.next()){
System.out.print("ID: "+rs.getInt("tutorial_id")+", ");
System.out.print("Title: "+rs.getString("tutorial_title")+", ");
System.out.print("Author: "+rs.getString("tutorial_author")+", ");
System.out.print("Submission date: "+rs.getDate("submission_date"));
//Retrieving the DATALINK object using the getURL() method
System.out.print("Tutorial link: "+rs.getURL("tutorial_link"));
System.out.println();
}
}
}输出
Connection established...... Contents of the table tutorials_data: ID: 1, Title: Java, Author: Krishna Kasyap, Submission date: 2019-09-01Tutorial link: https://tutorialspoint.com/java ID: 2, Title: JFreeCharts, Author: Satish Kumar, Submission date: 2019-05-01Tutorial link: https://tutorialspoint.com/jfreechart ID: 3, Title: Android, Author: Sai Ram, Submission date: 2019-03-01Tutorial link: https://tutorialspoint.com/android ID: 4, Title: Cassandra, Author: Pruthvi Raj, Submission date: 2019-04-06Tutorial link: https://tutorialspoint.com/cassandra ID: 5, Title: JavaFX, Author: Sarmista sharma, Submission date: 2018-05-01Tutorial link: https://tutorialspoint.com/javafx
更新于：2019年7月30日
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