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

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

其他回答

我可能找错了对象，但您的异常似乎表明您的MySQL服务器不可用。

线程main中出现异常: 日志含义通信链路故障最后一个成功发送到服务器的报文为0 毫秒前。驱动未收到服务器的报文。处理步骤在…

如果你尝试(从终端)会发生什么?

mysql -u username -p

系统将提示您输入与用户名关联的密码。在你给出正确的密码后，mysql客户端连接吗?

如果没有，你可能需要从首选项启动MySQL。您还可以将其设置为在启动时运行。

2010-06-06 10:03:51

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" );

2010-06-06 06:50:38

这可能是一个简单的罐子问题。可能您正在使用旧的mysql-connector-java- xxx -bin.jar，它不支持您当前的mysql版本。我使用mysql-connector-java-5.1.18-bin.jar，因为我使用mysql 5.5，这个问题为我解决了。

2014-11-04 05:10:03

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

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

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

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