如何在JDBC中使用try-with-resources？
每当我们实例化并使用某些对象/资源时，都应显式关闭它们，否则有可能发生资源泄漏。
通常，我们使用finally资源使用close资源作为-
Connection con = null;
Statement stmt = null;
ResultSet rs = null;
//注册驱动程序
try {
con = DriverManager.getConnection(mysqlUrl, "root", "password");
stmt = con.createStatement();
} catch (SQLException e) {
e.printStackTrace();
} finally {
try {
rs.close();
stmt.close();
con.close();
} catch(SQLException e) {
e.printStackTrace();
}
}从JSE7开始，引入了try-with-resources语句。在这种情况下，我们在try块中声明一个或多个资源，这些资源在使用后将自动关闭。（在try块的末尾）
我们在try块中声明的资源应扩展java.lang.AutoCloseable类。
在JDBC中，我们可以在try-with-resources语句中使用java.sql.CallableStatement，Connection，PreparedStatement，Statement，ResultSet和RowSet。
示例
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');以下JDBC程序演示了JDBC中try-with-resources语句的用法-
示例
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
public class TryWithResources_Example {
public static void main(String args[]) {
//获得连接
String mysqlUrl = "jdbc:mysql://localhost/mydatabase";
System.out.println("Connection established......");
//注册驱动程序
try(Connection con = DriverManager.getConnection(mysqlUrl, "root", "password");
Statement stmt = con.createStatement(); ) {
try(ResultSet rs = stmt.executeQuery("select * from MyPlayers");){
//检索数据
while(rs.next()) {
System.out.print(rs.getInt("ID")+", ");
System.out.print(rs.getString("First_Name")+", ");
System.out.print(rs.getString("Last_Name")+", ");
System.out.print(rs.getDate("Date_Of_Birth")+", ");
System.out.print(rs.getString("Place_Of_Birth")+", ");
System.out.print(rs.getString("Country"));
System.out.println();
}
} catch (SQLException e) {
e.printStackTrace();
}
} catch (SQLException e) {
e.printStackTrace();
}
}
}输出结果
Connection established...... 1, Shikhar, Dhawan, 1981-12-05, Delhi, India 2, Jonathan, Trott, 1981-04-22, CapeTown, SouthAfrica 3, Kumara, Sangakkara, 1977-10-27, Matale, Srilanka 4, Virat, Kohli, 1988-11-05, Mumbai, India 5, Rohit, Sharma, 1987-04-30, Nagpur, India 6, Ravindra, Jadeja, 1988-12-06, Nagpur, India 7, James, Anderson, 1982-06-30, Burnely, England 8, Ryan, McLaren, 1983-02-09, Kumberly, null