我写了个JDBC工具类,然后测试的时候报空指针异常,我用断点测试出是Class.forname()
这里是null,但是我驱动包之类的都加了啊!然后不死心的我又手写了一个测试类,Class.forname()
又可以连接,就是说工具类就不行,测试类就可以。
下面把代码贴上来,希望又前辈能够指正我的错误。
``
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
public class JDBCUtils {
private JDBCUtils(){}
private static Connection con = null;
static{
try{
Class.forName("com.mysql.jdbc.Driver");
String url = "jdbc:mysql://localhost:3306/mybase";
String username = "root";
String password = "123";
Connection con = DriverManager.getConnection(url,username,password);
}catch (ClassNotFoundException se){
se.printStackTrace();
System.out.println("数据库连接失败");
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
public static Connection getConnection(){
return con;
}
}
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
public class JDBCTest {
public static void main(String[] args) throws SQLException {
Connection con = JDBCUtils.getConnection();
PreparedStatement pst = con.prepareStatement("SELECT sname FROM sort");
ResultSet rs = pst.executeQuery();
while(rs.next()){
System.out.println(rs.getString("sname"));
}
}
}
上面是我工具类的测试类,下面我把报错信息贴一下
Exception in thread "main" java.lang.NullPointerException
at com.itheima.jdbcutil.JDBCTest.main(JDBCTest.java:13)
下面是我可以正常运行的测试类
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
public class JDBCTest2 {
public static void main(String[] args) throws ClassNotFoundException, SQLException {
Class.forName("com.mysql.jdbc.Driver");
Connection con = DriverManager.getConnection( "jdbc:mysql://localhost:3306/mybase","root","123");
PreparedStatement pst = con.prepareStatement("select sname from sort");
ResultSet rs = pst.executeQuery();
while(rs.next()){
System.out.println(rs.getString("sname"));
}
}
}