使用 JDBC 將 JAVA 與 MySql 連接

Question

這是我嘗試過的代碼。 但是每次它顯示錯誤：無法創建與數據庫服務器的連接。代碼中的錯誤是什么？url 語法是否正確？

import java.sql.*;
public class Second {
    public static void main(String[] args) {
        Connection con = null;
        try {
            String url = "jdbc:mysql://localhost:3306/sakila";
            String user = "root";
            String password = "1234";
            Class.forName("com.mysql.jdbc.Driver");
            con = DriverManager.getConnection(url, user, password); 
            System.out.println("Connection is established.");
            con.close();
        }
        catch(Exception e) {
            e.printStackTrace();
        }
    }
}

我在這里發布了 StackTrace。我得到的 Null 指針異常是什么？

Wed May 13 09:19:35 IST 2020 WARN: Establishing SSL connection without server's identity verification is not recommended. According to MySQL 5.5.45+, 5.6.26+ and 5.7.6+ requirements SSL connection must be established by default if explicit option isn't set. For compliance with existing applications not using SSL the verifyServerCertificate property is set to 'false'. You need either to explicitly disable SSL by setting useSSL=false, or set useSSL=true and provide truststore for server certificate verification.
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.newInstanceWithCaller(Constructor.java:500)
    at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:481)
    at mysql.connector.java@5.1.38/com.mysql.jdbc.Util.handleNewInstance(Util.java:404)
    at mysql.connector.java@5.1.38/com.mysql.jdbc.Util.getInstance(Util.java:387)
    at mysql.connector.java@5.1.38/com.mysql.jdbc.SQLError.createSQLException(SQLError.java:917)
    at mysql.connector.java@5.1.38/com.mysql.jdbc.SQLError.createSQLException(SQLError.java:896)
    at mysql.connector.java@5.1.38/com.mysql.jdbc.SQLError.createSQLException(SQLError.java:885)
    at mysql.connector.java@5.1.38/com.mysql.jdbc.SQLError.createSQLException(SQLError.java:860)
    at mysql.connector.java@5.1.38/com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2332)
    at mysql.connector.java@5.1.38/com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2085)
    at mysql.connector.java@5.1.38/com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:795)
    at mysql.connector.java@5.1.38/com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:44)
    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.newInstanceWithCaller(Constructor.java:500)
    at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:481)
    at mysql.connector.java@5.1.38/com.mysql.jdbc.Util.handleNewInstance(Util.java:404)
    at mysql.connector.java@5.1.38/com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:400)
    at mysql.connector.java@5.1.38/com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:327)
    at java.sql/java.sql.DriverManager.getConnection(DriverManager.java:677)
    at java.sql/java.sql.DriverManager.getConnection(DriverManager.java:228)
    at JDBC.Second.main(Second.java:12)
Caused by: java.lang.NullPointerException
    at mysql.connector.java@5.1.38/com.mysql.jdbc.ConnectionImpl.getServerCharset(ConnectionImpl.java:3005)
    at mysql.connector.java@5.1.38/com.mysql.jdbc.MysqlIO.sendConnectionAttributes(MysqlIO.java:1916)
    at mysql.connector.java@5.1.38/com.mysql.jdbc.MysqlIO.proceedHandshakeWithPluggableAuthentication(MysqlIO.java:1845)
    at mysql.connector.java@5.1.38/com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1215)
    at mysql.connector.java@5.1.38/com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2255)
    at mysql.connector.java@5.1.38/com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2286)
    ... 14 more

Answer 1

您的連接 url 應該是 jdbc:mysql://localhost:3306/sakila?autoReconnect=true&useSSL=false