无法从 java 连接到 mysql 服务器

Question

我在这行代码收到错误 "Communications link failure"：

mySqlCon = DriverManager.getConnection("jdbc:mysql://**server ip address**:3306/db-name", "mu-user-name", "my-password");

我检查了 this post 中的所有内容：

我在 etc/mysql 中增加了 my.cnf 中的最大允许数据包： max_allowed_packet = 5073741824------ [mysql转储] max_allowed_packet = 1G
绑定地址为：127.0.0.1
所有超时值都等于一个数字
Tomcat 尚未安装在服务器上（新服务器）
my.cnf
我可以ping通服务器
我通过 ssh

当我将查询字符串更改为：

mySqlCon = DriverManager.getConnection("jdbc:mysql://**server ip address**:22/127.0.0.1:3306/db-name", "mu-user-name", "my-password");

我收到错误 Packet for query is too large (4739923 > 1048576). You can change this value on the server by setting the max_allowed_packet' variable.

虽然我在 my.cnf 上更改了数据包大小并在之后重新启动了 mysql 服务。

有什么建议吗？

注意：

我可以用这段代码通过ssh连接，但这种方式似乎不太合理！我可以在 main 中连接一次，然后我应该将连接传递给所有类.

public my-class-constructor() {

        try {
            go();
        } catch (Exception e) {
            e.printStackTrace();
        }

        mySqlCon = null;
        String driver = "com.mysql.jdbc.Driver";
        String url = "jdbc:mysql://" + rhost + ":" + lport + "/";
        String db = "my-db-name";
        String dbUser = "dbuser";
        String dbPasswd = "pass";
        try {
            Class.forName(driver);
            mySqlCon = DriverManager.getConnection(url + db, dbUser, dbPasswd);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public static void go() {
        String user = "ssh-user";
        String password = "ssh-pass";
        String host = "ips-address";
        int port = 22;
        try {
            JSch jsch = new JSch();
            Session session = jsch.getSession(user, host, port);
            lport = 4321;
            rhost = "localhost";
            rport = 3306;
            session.setPassword(password);
            session.setConfig("StrictHostKeyChecking", "no");
            System.out.println("Establishing Connection...");
            session.connect();
            int assinged_port = session.setPortForwardingL(lport, rhost, rport);
            System.out.println("localhost:" + assinged_port + " -> " + rhost
                    + ":" + rport);
        } catch (Exception e) {
            System.err.print(e);
            e.printStackTrace();
        }
    }

Answer 1

看看here。看起来下面描述了你的情况

The largest possible packet that can be transmitted to or from a MySQL 5.7 server or client is 1GB.

When a MySQL client or the mysqld server receives a packet bigger than max_allowed_packet bytes, it issues an ER_NET_PACKET_TOO_LARGE error and closes the connection. With some clients, you may also get a Lost connection to MySQL server during query error if the communication packet is too large.

Both the client and the server have their own max_allowed_packet variable, so if you want to handle big packets, you must increase this variable both in the client and in the server.

所以，看起来您还需要更改客户端上的 max_allowed_packet：

mySqlCon = DriverManager.getConnection("jdbc:mysql://**server ip address**:3306/db-name?max_allowed_packet= 5073741824", "mu-user-name", "my-password");

Answer 2

我把/etc/mysql中的my.cnf文件中的绑定地址改成了服务器的ip地址，问题就解决了

无法从 java 连接到 mysql 服务器

Cannot connect to mysql server from java

java

mysql

database-connection