请问为啥这段java程序报错呢？
import java.sql.*;
public class Gradation { //创建类
//连接数据库方法
public Connection getConnection() throws ClassNotFoundException, SQLException {
Class.forName("com.mysql.cj.jdbc.Driver");
Connection connection = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3360/test", "root", "root8888");
return connection; //返回Connection对象
}
public static void main(String[] args) { //主方法
Gradation gradation = new Gradation(); //创建本类对象
Connection connection = null; //声明connection对象
Statement statement = null; //声 明Statement对象
ResultSet result = null; //声明ResultSet对象
try {
connection = gradation.getConnection(); //与数据库建立连接
statement = (Statement) connection.createStatement(); //实例话Statement对象
result = statement.executeQuery("select * from tb_stu"); //执行SQL语句，返回结果集
while (result.next()) { //如果当前语句不是最后一条则进入循环
String idString = result.getString("id");
String nameString = result.getString("name");
String sexString = result.getString("sex");
//获取列名是birthday的字段值
String birthdayString = result.getString("birthday");
System.out.println("编号：" + idString);
System.out.println("姓名：" + nameString);
System.out.println("性别：" + sexString);
System.out.println("生日：" + birthdayString);
}
} catch (Exception e) {
e.printStackTrace();
} finally { //依次关闭数据库资源
if (result != null) {
try {
result.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if (statement != null) {
try {
((Connection) statement).close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if (connection != null) {
try {
connection.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
}
}
com.mysql.cj.jdbc.exceptions.CommunicationsException: Communications link failure
The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.
at mysql.connector.java@8.0.24/com.mysql.cj.jdbc.exceptions.SQLError.createCommunicationsException(SQLError.java:174)
at mysql.connector.java@8.0.24/com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:64)
at mysql.connector.java@8.0.24/com.mysql.cj.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:833)
at mysql.connector.java@8.0.24/com.mysql.cj.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:453)
at mysql.connector.java@8.0.24/com.mysql.cj.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:246)
at mysql.connector.java@8.0.24/com.mysql.cj.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:198)
at java.sql/java.sql.DriverManager.getConnection(DriverManager.java:677)
at java.sql/java.sql.DriverManager.getConnection(DriverManager.java:228)
at Gradation.getConnection(Gradation.java:7)
at Gradation.main(Gradation.java:17)
Caused by: com.mysql.cj.exceptions.CJCommunicationsException: Communications link failure
The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.
at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:78)
at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.base/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:499)
at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:480)
at mysql.connector.java@8.0.24/com.mysql.cj.exceptions.ExceptionFactory.createException(ExceptionFactory.java:61)
at mysql.connector.java@8.0.24/com.mysql.cj.exceptions.ExceptionFactory.createException(ExceptionFactory.java:105)
at mysql.connector.java@8.0.24/com.mysql.cj.exceptions.ExceptionFactory.createException(ExceptionFactory.java:151)
at mysql.connector.java@8.0.24/com.mysql.cj.exceptions.ExceptionFactory.createCommunicationsException(ExceptionFactory.java:167)
at mysql.connector.java@8.0.24/com.mysql.cj.protocol.a.NativeSocketConnection.connect(NativeSocketConnection.java:89)
at mysql.connector.java@8.0.24/com.mysql.cj.NativeSession.connect(NativeSession.java:144)
at mysql.connector.java@8.0.24/com.mysql.cj.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:953)
at mysql.connector.java@8.0.24/com.mysql.cj.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:823)
... 7 more
Caused by: java.net.ConnectException: Connection refused
at java.base/sun.nio.ch.Net.connect0(Native Method)
at java.base/sun.nio.ch.Net.connect(Net.java:576)
at java.base/sun.nio.ch.Net.connect(Net.java:565)
at java.base/sun.nio.ch.NioSocketImpl.connect(NioSocketImpl.java:588)
at java.base/java.net.SocksSocketImpl.connect(SocksSocketImpl.java:333)
at java.base/java.net.Socket.connect(Socket.java:645)
at mysql.connector.java@8.0.24/com.mysql.cj.protocol.StandardSocketFactory.connect(StandardSocketFactory.java:155)
at mysql.connector.java@8.0.24/com.mysql.cj.protocol.a.NativeSocketConnection.connect(NativeSocketConnection.java:63)
... 10 more
连接数据库错误，主要是你犯了下面其中之一：
1.账号密码错误
2.端口号错误，mysql默认端口号是3306，你有没有改成3360？
3.确定你的mysql版本是8.0或者以上，否则驱动不能写com.mysql.cj.jdbc.Driver，而是com.mysql.jdbc.Driver
4.链接驱动jar包要和你安装的mysql版本一致
5.上面都没错的情况下，你的链接信息后面加上这个
?useUnicode=true&characterEncoding=utf8
第七行代码这样写
Connection connection = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3360/test?useUnicode=true&characterEncoding=utf8", "root", "root8888");
连接数据库错误。你确定你的端口是3360，而不是3306？
mysql服务没有启动吧，看下服务中的mysql有没有启动，下图是启动的。
解决措施：搜索服务->右击mysql->选择启动,
把第七行代码的
Connection connection = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3360/test", "root", "root8888");3360改成3306
1.你第七行代码有错误,将3360改成3306
Connection connection = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/test", "root", "root8888");
2.确保你电脑mysql服务启动了,安装了mysql,如果没有,你可以检查一下
3.如果还不行,可能是你的mysql-driver中的jar驱动版本不一致,您可以换一下
Communications link failure：数据库连接失败，应该是你的jar报版本有问题，com.mysql.cj.jdbc.Driver这个有问题。
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