java连接数据库异常

Question

为什么java获取mysql数据库失败

MySQL是8.0版本

已经打开防火墙端口权限了，还有root权限为%了

运行后报错的文本：

com.mysql.jdbc.exceptions.jdbc4.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 java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:77)
    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 com.mysql.jdbc.Util.handleNewInstance(Util.java:425)
    at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:989)
    at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:341)
    at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2192)
    at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2225)
    at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2024)
    at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:779)
    at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:47)
    at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:77)
    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 com.mysql.jdbc.Util.handleNewInstance(Util.java:425)
    at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:389)
    at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:330)
    at java.sql/java.sql.DriverManager.getConnection(DriverManager.java:681)
    at java.sql/java.sql.DriverManager.getConnection(DriverManager.java:229)
    at net.jdbc.main(jdbc.java:12)
Caused by: java.net.UnknownHostException: 不知道这样的主机。 (locallhost)
    at java.base/java.net.Inet6AddressImpl.lookupAllHostAddr(Native Method)
    at java.base/java.net.InetAddress$PlatformNameService.lookupAllHostAddr(InetAddress.java:933)
    at java.base/java.net.InetAddress.getAddressesFromNameService(InetAddress.java:1519)
    at java.base/java.net.InetAddress$NameServiceAddresses.get(InetAddress.java:852)
    at java.base/java.net.InetAddress.getAllByName0(InetAddress.java:1509)
    at java.base/java.net.InetAddress.getAllByName(InetAddress.java:1367)
    at java.base/java.net.InetAddress.getAllByName(InetAddress.java:1301)
    at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.java:188)
    at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:300)
    ... 16 more

```java
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

public class jdbc {
    public static void main(String[] args) {
        Connection conn = null;
        try {
            Class.forName("com.mysql.jdbc.Driver");
            conn =  DriverManager.getConnection("jdbc:mysql://localhost:3306/gxgl", "root", "123456");
            System.out.print("数据库连接成功");
        } catch (Exception e) {
            e.printStackTrace();
        }
        finally {
            if(null!=conn) {
                try {
                    conn.close();
                    System.out.print("关闭数据库连接");
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
        }
        
    }

}

是用这个代码运行的

Answer 1

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• 你可以参考下这个问题的回答, 看看是否对你有帮助, 链接: https://ask.csdn.net/questions/30100
• 我还给你找了一篇非常好的博客，你可以看看是否有帮助，链接：Java连接Mysql数据库写入中文数据乱码成？？？的解决方法
• 除此之外, 这篇博客: MySQL压缩包版安装教程（韩顺平java基础版）中的 修改root用户密码 部分也许能够解决你的问题, 你可以仔细阅读以下内容或跳转源博客中阅读:
  

  

  user mysql;

  updata user set authentcation_string=password(‘hsp’) where user=‘root’ and Host=‘localhost’;

  上面的语句就是修改 root用户的密码为 hsp

  注意：在后面需要带分号，回车即执行该指令

  执行：flush privileges；刷新权限

  退出：quit

如果你已经解决了该问题, 非常希望你能够分享一下解决方案, 写成博客, 将相关链接放在评论区, 以帮助更多的人 ^-^