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

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

其他回答

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

2014-11-13 10:05:05

如果您使用WAMP或XAMP服务器安装mysql数据库。然后你必须显式启动mysql服务器，否则它会显示 com.mysql.jdbc.exceptions.jdbc4。CommunicationsException:连接数据库时通信链路故障

2014-11-04 05:19:02

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

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

我刚开始申请的时候也遇到过同样的问题，

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.

问题是在mysql文件/etc/mysql/mysql.conf.d/mysqld.cnf中，配置是这样的

[mysqld]
pid-file        = /var/run/mysqld/mysqld.pid
socket          = /var/run/mysqld/mysqld.sock
datadir         = /var/lib/mysql
log-error       = /var/log/mysql/error.log
# By default we only accept connections from localhost
bind-address    = 127.0.0.1
# Disabling symbolic-links is recommended to prevent assorted security risks
symbolic-links=0

所以我们可以看到，绑定地址是指向127.0.0.1，所以启动你的应用程序，一个简单的解决方案是，我们可以使用jdbc:mysql://127.0.0.1:3306/pizzeria，而不是jdbc:mysql://localhost:3306/pizzeria，将mysql连接到应用程序或另一个解决方案是，你可以检查和改变mysql配置为默认值。两种方案都可行。我希望这对你们也有用。

2018-11-03 06:54:50

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

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