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

我得到了同样的错误，因为我试图运行我的程序没有启动mysql服务器。

启动mysql服务器后，一切正常。

2013-04-04 04:53:55

其他回答

前面的答案是合适的。但是，我还想指出一个更普遍的问题。

我也遇到过类似的问题，原因是我所在公司的网络限制。

当我在任何其他网络时，同样的连接都是成功的。

2016-12-22 10:36:40

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

通常，当您使用的数据库在操作系统中关闭时，会出现此问题。如果你使用windows，那么进入服务，确保MySQL是启动位置。

2022-04-03 00:47:49

用于远程调用Mysql

Add remote user to Mysql from for exemple IP=remoteIP : mysql -u xxxx -p //local coonection to mysql mysql> GRANT ALL PRIVILEGES ON *.* TO 'theNewUser'@'remoteIP' IDENTIFIED BY 'passWord'; //Query OK, 0 rows affected (xx sec) mysql> FLUSH PRIVILEGES; //Query OK, 0 rows affected Allow remote access to Mysql (by default all externall call is not allowed): Edit /etc/mysql/mysql.conf.d/mysqld.cnf or /etc/mysql/my.cnf Change line: bind-address = 127.0.0.1 to bind-address = 0.0.0.0 Restart Mysql: /etc/init.d/mysql restart For The latest version of JDBC Driver, the JDBC : jdbc.url='jdbc:mysql://remoteIP:3306/yourDbInstance?autoReconnect=true&useUnicode=true&useJDBCCompliantTimezoneShift=true&useLegacyDatetimeCode=false&serverTimezone=UTC' jdbc.user='theNewUser'

2018-11-07 21:06:19

我收到了多个错误，如:

CommunicationsException:通信链路故障 java.lang.NullPointerException:尝试在空对象引用上调用接口方法'java.sql.Statement java.sql.Connection.createStatement()'。

我必须补充一句:

在AndroidManifest.xml中包含<uses-permission android:name="android.permission. xml "。INTERNET"/>就在开始清单标签之后。将JDBC驱动程序添加到您的Gradle(或Maven)依赖项中。

2019-02-10 15:30:37

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

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