package jdbc;
 ?
         import org.junit.jupiter.api.Test;
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         import java.sql.Connection;
         import java.sql.DriverManager;
         import java.sql.SQLException;
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 public class JDBCUtils {
     public static Connection connection;
     private static String url="jdbc:mysql://localhost:3306/aaa?useUnicode=true&characterEncoding=utf-8";
     private static String username="root";
     private static String password="root";
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     static{
         try {
             Class.forName("com.mysql.jdbc.Driver");
             connection = DriverManager.getConnection(url,username,password);
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         } catch (ClassNotFoundException e) {
             e.printStackTrace();
         } catch (SQLException e) {
             e.printStackTrace();
         }
     }
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     public static Connection getConnection(){
         return connection;
     }
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     @Test
     public void test(){
         Connection connection = JDBCUtils.getConnection();
         System.out.println(connection);
     }
 }

 url=jdbc:mysql://localhost:3306/aaa?useUnicode=true&characterEncoding=utf-8
 username=root
 password=root

package jdbc;
 ?
 import org.junit.jupiter.api.Test;
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 import java.io.FileInputStream;
 import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.sql.Connection;
 import java.sql.DriverManager;
 import java.sql.SQLException;
 import java.util.Properties;
 ?
 public class JDBCUtils2 {
     private static Connection connection;
     private static String url;
     private static String username;
     private static String password;
 ?
     static {
         try {
             //动态加载驱动
             Class.forName("com.mysql.jdbc.Driver");
             //加载配置文件
             Properties properties = new Properties();
             properties.load(new FileInputStream("src/main/java/db.properties"));
             url = properties.getProperty("url");
             username = properties.getProperty("username");
             password = properties.getProperty("password");
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             connection = DriverManager.getConnection(url,username,password);
 ?
 ?
         } catch (ClassNotFoundException e) {
             e.printStackTrace();
         } catch (FileNotFoundException e) {
             e.printStackTrace();
         } catch (IOException e) {
             e.printStackTrace();
         } catch (SQLException e) {
             e.printStackTrace();
         }
     }
 ?
     public static Connection getConnection(){
         return connection;
     }
 ?
     @Test
     public void test(){
         Connection connection = JDBCUtils2.getConnection();
         System.out.println(connection);
     }
 }