我正在尝试连接到我在

Java程序中使用

MySQL创建的数据库,但它总是失败.

为了举例,这是我的代码：

import java.sql.*;

public class Squirrel {

public static void main(String[] args) {

String user;

String password;

Connection connection;

Statement statement;

try {

Class.forName("com.mysql.jdbc.Driver");

connection = DriverManager.getConnection(

"jdbc:mysql://localhost:3306", user, password);

statement = connection.createStatement();

// Other code

} catch (ClassNotFoundException | SQLException e) {

e.printStackTrace();

} finally {

try {

if (statement != null) {

statement.close();

}

if (connection != null) {

connection.close();

}

} catch (SQLException e) {

e.printStackTrace();

}

}

}

}

我能够从IntelliJ中连接到数据库,并添加了添加到项目中的mysql-connector-java-5.1.40.jar,但每次运行程序时,DriverManager.getConnection()都会抛出：

com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Could not create connection to database server.

at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)

at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)

at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)

at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:488)

at com.mysql.jdbc.Util.handleNewInstance(Util.java:425)

at com.mysql.jdbc.Util.getInstance(Util.java:408)

at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:918)

at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:897)

at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:886)

at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:860)

at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2330)

at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2083)

at com.mysql.jdbc.ConnectionImpl.(ConnectionImpl.java:806)

at com.mysql.jdbc.JDBC4Connection.(JDBC4Connection.java:47)

at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)

at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)

at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)

at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:488)

at com.mysql.jdbc.Util.handleNewInstance(Util.java:425)

at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:410)

at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:328)

at java.sql/java.sql.DriverManager.getConnection(DriverManager.java:678)

at java.sql/java.sql.DriverManager.getConnection(DriverManager.java:229)

at Squirrel.main(Squirrel.java:12)

Caused by: java.lang.NullPointerException

at com.mysql.jdbc.ConnectionImpl.getServerCharset(ConnectionImpl.java:2997)

at com.mysql.jdbc.MysqlIO.sendConnectionAttributes(MysqlIO.java:1934)

at com.mysql.jdbc.MysqlIO.proceedHandshakeWithPluggableAuthentication(MysqlIO.java:1863)

at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1226)

at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2253)

at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2284)

... 13 more