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2024-03-29 05:00:04

com.mysql.jdbc.exceptions.jdbc4。CommunicationsException:通信链路故障

我正在努力让我的数据库与我的Java程序对话。

有人能给我一个使用JDBC的快速而简单的示例程序吗?

我得到了一个相当大的错误

Exception in thread "main" com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure 
    The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:409)
    at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1122)
    at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2260)
    at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:787)
    at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:49)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:409)
    at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:357)
    at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:285)
    at java.sql.DriverManager.getConnection(DriverManager.java:582)
    at java.sql.DriverManager.getConnection(DriverManager.java:207)
    at SqlTest.main(SqlTest.java:22)
Caused by: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
    The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:409)
    at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1122)
    at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:344)
    at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2181)
    ... 12 more
Caused by: java.net.ConnectException: Connection refused
    at java.net.PlainSocketImpl.socketConnect(Native Method)
    at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:333)
    at java.net.PlainSocketImpl.connectToAddress(PlainSocketImpl.java:195)
    at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:182)
    at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:432)
    at java.net.Socket.connect(Socket.java:529)
    at java.net.Socket.connect(Socket.java:478)
    at java.net.Socket.<init>(Socket.java:375)
    at java.net.Socket.<init>(Socket.java:218)
    at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.java:256)
    at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:293)
    ... 13 more

测试文件内容:

import com.mysql.jdbc.*;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

public class SqlTest {

    public static void main(String [] args) throws Exception {
        // Class.forName( "com.mysql.jdbc.Driver" ); // do this in init
        // // edit the jdbc url 
        Connection conn = DriverManager.getConnection( 
            "jdbc:mysql://localhost:3306/projects?user=user1&password=123");
        // Statement st = conn.createStatement();
        // ResultSet rs = st.executeQuery( "select * from table" );

        System.out.println("Connected?");
    }
}

当前回答

示例jdbc连接类文件。当你想要获得一个连接时，简单地调用getConnection方法。包含相关的mysql-connector.jar

import java.sql.Connection;
import java.sql.DriverManager;


public class DBConnection {

    public Connection getConnection() {
        Connection con = null;

        String dbhost;
        String user;
        String password;
// get properties
dbhost="jdbc:mysql://localhost:3306/cardmaildb";
user="root";
password="123";

 System.out.println("S=======db Connecting======");

        try {
            Class.forName("com.mysql.jdbc.Driver");

            con = DriverManager.getConnection(dbhost, user, password);
            //if you are facing with SSl issue please try this 
            //con = DriverManager.getConnection("jdbc:mysql://192.168.23.100:3306/cardmaildb?useUnicode=yes&characterEncoding=UTF-8&useSSL=false",user, password);

        } catch (Exception e) {
            System.err.println("error in connection");
            e.printStackTrace();
        }
        System.out.println("E=======db Connecting======");
        return con;
    }

    public static void main(String[] args) {
        new DBConnection().getConnection();
    }
}
2019-12-31 06:42:12

其他回答

在我的例子中，我需要将Localhost替换为实际的数据库服务器IP地址

而不是

 Connection con = DriverManager.getConnection(
 "jdbc:mysql://localhost:3306/DBname", "root", "root");

我需要

 Connection con = DriverManager.getConnection(
 "jdbc:mysql://192.100.0.000:3306/DBname", "root", "root");
2014-03-12 10:32:07

在MySQL Workbench中，有一种非常特殊的情况会发生这种问题，特别是在使用Eclipse JPA和本地主机下的持久性时。问题是，正如在其他一些回答中提到的，MySQL服务器在创建连接时可以非常严格地使用localhost, 0.0.0.0.1或127.0.0.1。为了克服这个问题，在(Windows)中的hosts文件:

C:\Windows\System32\drivers\etc

需要为主连接(例如myserver)添加以下条目:

#我的数据库服务器 127.0.0.1 myserver

如果没有添加到主机，那么每次尝试从127.0.0.1连接数据库时，连接都会失败

2022-04-17 18:34:28

如果有任何读者在访问远程服务器时遇到此问题:请确保端口是打开的

2016-12-28 13:11:34

尝试将localhost更改为127.0.0.1。

本地主机将被解析为::1。MySQL默认不支持IPv6连接。

下面是telnet localhost 3306的输出:

$ telnet localhost 3306
Trying ::1...

MySQL服务器没有响应。

当然，请确保您的MySQL服务器正在运行。

2017-05-18 01:24:51

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?

2010-06-06 17:40:40

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