如果Java试图通过SSL连接MySQL，但出现了错误，也可能发生此错误。(在我的例子中，我将Payara Server 5.193.1连接池配置为MySQL。)

有人建议设置useSSL=false。但是，由于Connector/J版本8.0.13，该设置已弃用。下面是MySQL连接器/J 8.0配置属性的摘录:

sslMode By default, network connections are SSL encrypted; this property permits secure connections to be turned off, or a different levels of security to be chosen. The following values are allowed: DISABLED - Establish unencrypted connections; PREFERRED - (default) Establish encrypted connections if the server enabled them, otherwise fall back to unencrypted connections; REQUIRED - Establish secure connections if the server enabled them, fail otherwise; VERIFY_CA - Like REQUIRED but additionally verify the server TLS certificate against the configured Certificate Authority (CA) certificates; VERIFY_IDENTITY - Like VERIFY_CA, but additionally verify that the server certificate matches the host to which the connection is attempted. This property replaced the deprecated legacy properties useSSL, requireSSL, and verifyServerCertificate, which are still accepted but translated into a value for sslMode if sslMode is not explicitly set: useSSL=false is translated to sslMode=DISABLED; {"useSSL=true", "requireSSL=false", "verifyServerCertificate=false"} is translated to sslMode=PREFERRED; {"useSSL=true", "requireSSL=true", "verifyServerCertificate=false"} is translated to sslMode=REQUIRED; {"useSSL=true" AND "verifyServerCertificate=true"} is translated to sslMode=VERIFY_CA. There is no equivalent legacy settings for sslMode=VERIFY_IDENTITY. Note that, for ALL server versions, the default setting of sslMode is PREFERRED, and it is equivalent to the legacy settings of useSSL=true, requireSSL=false, and verifyServerCertificate=false, which are different from their default settings for Connector/J 8.0.12 and earlier in some situations. Applications that continue to use the legacy properties and rely on their old default settings should be reviewed. The legacy properties are ignored if sslMode is set explicitly. If none of sslMode or useSSL is set explicitly, the default setting of sslMode=PREFERRED applies. Default: PREFERRED Since version: 8.0.13

因此，在我的例子中，设置sslMode=DISABLED就是解决这个问题所需要的全部内容。 这是在一台测试机器上。但是对于生产环境，安全解决方案应该正确配置Java客户机和MySQL服务器以使用SSL。

注意，通过禁用SSL，您可能还必须设置allowPublicKeyRetrieval=true。(同样，从安全角度来看，这不是一个明智的决定)。进一步的信息提供在MySQL ConnectionString选项:

AllowPublicKeyRetrieval If the user account uses sha256_password authentication, the password must be protected during transmission; TLS is the preferred mechanism for this, but if it is not available then RSA public key encryption will be used. To specify the server’s RSA public key, use the ServerRSAPublicKeyFile connection string setting, or set AllowPublicKeyRetrieval=True to allow the client to automatically request the public key from the server. Note that AllowPublicKeyRetrieval=True could allow a malicious proxy to perform a MITM attack to get the plaintext password, so it is False by default and must be explicitly enabled.

我的防火墙阻止了我的MySQL监听的3307帖子。所以我把端口从3307改成了3306。然后我就可以成功地连接到数据库。

也许你没有启动你的Mysql和Apache服务器。我从XAMPP控制面板启动Apache服务器和Mysql后，连接成功建立。

好运！

当我在my.ini和php.ini文件中将mysql端口从3306更改为3307时，就发生了这种情况，但在更改端口(3307->3306)后，它又可以正常工作了。

在我的情况下，原来是mysql-connector-java的版本太旧了。

在我的演示中，我像这样使用mysql-connector-java:

<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>5.1.9</version>
</dependency>

但是在开发环境中，我使用这个:

<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>5.1.31</version>
</dependency>

我的MySQL版本是5.1.48(是的，它是旧的，只是为了模仿产品版本)。所以我遇到了同样的错误。

既然找到了原因，解决办法也就找到了。匹配版本!

你有一个

com.mysql.jdbc.exceptions.jdbc4。CommunicationsException:通信链路故障 connectexception:拒绝连接

我引用了这个答案，其中还包含一个循序渐进的MySQL+JDBC教程:

If you get a SQLException: Connection refused or Connection timed out or a MySQL specific CommunicationsException: Communications link failure, then it means that the DB isn't reachable at all. This can have one or more of the following causes: IP address or hostname in JDBC URL is wrong. Hostname in JDBC URL is not recognized by local DNS server. Port number is missing or wrong in JDBC URL. DB server is down. DB server doesn't accept TCP/IP connections. DB server has run out of connections. Something in between Java and DB is blocking connections, e.g. a firewall or proxy. To solve the one or the other, follow the following advices: Verify and test them with ping. Refresh DNS or use IP address in JDBC URL instead. Verify it based on my.cnf of MySQL DB. Start the DB. Verify if mysqld is started without the --skip-networking option. Restart the DB and fix your code accordingly that it closes connections in finally. Disable firewall and/or configure firewall/proxy to allow/forward the port.

参见:

我应该如何连接到JDBC数据库/数据源在一个基于servlet的应用程序? 在多线程系统中使用静态java.sql.Connection实例安全吗?