java - 通过jdbc连接mysql异常

Question

当我尝试通过 jdbc 连接 mysql 时出现异常。已经有人问过这种类型的问题，但我没有找到解决问题的方法，这是我的代码...

    public static void main(String[] args) {
    String url="jdbc:mysql://localhost:3306/student?
    autoReconnect=true&useSSL=false";
    String user="root";
    String pass="system";
    try {
        Class.forName("com.mysql.jdbc.Driver");

        System.out.println("Now connecting to databse...\n");
        Connection con=DriverManager.getConnection(url,user,pass);
        System.out.println("Connected !!!\n");
        con.close();
        System.out.println("connection close !!!\n");

    } catch (ClassNotFoundException | SQLException e) {System.out.println(e);
   e.printStackTrace();
    }
}

这些是我得到的异常...

run:
Now connecting to databse...

com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Could not create connection to database server. Attempted reconnect 3 times. Giving up.
com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Could not create connection to database server. Attempted reconnect 3 times. Giving up.
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:404)
    at com.mysql.jdbc.Util.getInstance(Util.java:387)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:917)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:896)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:885)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:860)
    at com.mysql.jdbc.ConnectionImpl.connectWithRetries(ConnectionImpl.java:2165)
    at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2090)
    at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:795)
    at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:44)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:404)
    at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:400)
    at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:327)
    at java.sql.DriverManager.getConnection(DriverManager.java:664)
    at java.sql.DriverManager.getConnection(DriverManager.java:247)
    at dbms_basic.Dbms_Basic.main(Dbms_Basic.java:28)
Caused by: java.lang.NullPointerException
    at com.mysql.jdbc.ConnectionImpl.getServerCharset(ConnectionImpl.java:3005)
    at com.mysql.jdbc.MysqlIO.sendConnectionAttributes(MysqlIO.java:1916)
    at com.mysql.jdbc.MysqlIO.proceedHandshakeWithPluggableAuthentication(MysqlIO.java:1845)
    at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1215)
    at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2255)
    at com.mysql.jdbc.ConnectionImpl.connectWithRetries(ConnectionImpl.java:2106)
    ... 13 more
BUILD SUCCESSFUL (total time: 4 seconds)

有人帮我解决这个错误..

Answer 1

当您尝试在 Mysql 8 或更高版本的数据库上使用 Mysql 5 JDBC 驱动程序时，会发生此错误。您可以使用以下 JAR 文件

mysql-connector-java 8.0.11

或者使用这个 Maven 依赖

    <!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>8.0.11</version>
    </dependency>

如果你需要在同一个应用程序中同时连接到 MySQL 5 和 MySQL 8，你将需要隔离类加载器，类似下面的方法可能会起作用

How to load JAR files dynamically at Runtime?