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.

如果您更改了端口，则会得到这种错误"com.mysql.jdbc.exceptions.jdbc4 "。CommunicationsException:通信链路故障 请检查你的端口号

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!

下载MySQL-JDBC-Type-4-Treiber (i.g。Mysql -connector-java-5.1.11-bin.jar从Mysql -connector-java-5.1.11.zip)

在编译和运行时期间，您需要在类路径中包含驱动程序jar。

Class.forName( "com.mysql.jdbc.Driver" ); // do this in init
// edit the jdbc url 
Connection conn = DriverManager.getConnection( "jdbc:mysql://MyDbComputerNameOrIP:3306/myDatabaseName", username, password );
Statement st = conn.createStatement();
ResultSet rs = st.executeQuery( "select * from table" );

在我的案例中，解决方案是将预期的TLS协议添加到连接字符串中，如下所示:

jdbc:mysql://localhost:3306/database_name?enabledTLSProtocols=TLSv1.2

出于测试/开发的目的(不推荐用于生产)，您还可以尝试:

jdbc:mysql://localhost:3306/database_name?useSSL=false&allowPublicKeyRetrieval=true

在我的例子中，我遇到了这个问题。当我试图通过IntelliJ Idea数据源连接到AWS RDS MySQL时，CommunicationsException:通信链路故障)。

这个视频帮助了我: https://www.youtube.com/watch?v=v3jH1YxJqaY