java - 使用 JDBC 连接 JAVA 和 MySql

Question

这是我尝试过的代码。但每次都会显示错误:无法创建与数据库服务器的连接。代码中的错误是什么？url语法是否正确？

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();
        }
    }
}

我已在此处发布了 StackTrace。我收到的空指针异常是什么？

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

您的连接网址应该是 jdbc:mysql://localhost:3306/sakila?autoReconnect=true&useSSL=false