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

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

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

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

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

我也遇到过同样的问题，我是这样解决的:

中的.jsp调用了尚未定义的属性 servlet。我有两个列名，我通过ResultSet (getString("columnName"))传递到一个对象，这与我的数据库中的列名不匹配。

我不太确定哪一个解决了这个问题，但它确实有效。另外，请确保为每个表查询创建了一个新的Statement和ResultSet。

2014-03-17 05:34:49

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

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