我在网络服务器中托管了一个MySQL数据库。我已经授予所有权限并允许我的IP从我的本地计算机远程连接到这个数据库。它已连接，我能够从数据库中检索数据到我的 Java Swing 应用程序。但是，有时我收到此错误消息并且我与托管数据库的连接失败。 错误如下所示:

Apr 7, 2012 12:49:20 AM scm.new_fas txtSearchKeyReleased
SEVERE: null
com.mysql.jdbc.CommunicationsException: Communications link failure due to underlying exception: 

** BEGIN NESTED EXCEPTION ** 

java.io.EOFException
MESSAGE: Can not read response from server. Expected to read 4 bytes, read 0 bytes before connection was unexpectedly lost.

STACKTRACE:

java.io.EOFException: Can not read response from server. Expected to read 4 bytes, read 0 bytes before connection was unexpectedly lost.
    at com.mysql.jdbc.MysqlIO.readFully(MysqlIO.java:1997)
    at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:2411)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:2916)
    at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1631)
    at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:1723)
    at com.mysql.jdbc.Connection.execSQL(Connection.java:3250)
    at com.mysql.jdbc.Connection.execSQL(Connection.java:3179)
    at com.mysql.jdbc.Statement.executeQuery(Statement.java:1207)
    at scm.DBControl.getResult(DBControl.java:49)
    at scm.new_fas.txtSearchKeyReleased(new_fas.java:1686)
    at scm.new_fas.access$2300(new_fas.java:28)
    at scm.new_fas$23.keyReleased(new_fas.java:1136)
    at java.awt.Component.processKeyEvent(Component.java:5999)
    at javax.swing.JComponent.processKeyEvent(JComponent.java:2794)
    at java.awt.Component.processEvent(Component.java:5815)
    at java.awt.Container.processEvent(Container.java:2058)
    at java.awt.Component.dispatchEventImpl(Component.java:4410)
    at java.awt.Container.dispatchEventImpl(Container.java:2116)
    at java.awt.Component.dispatchEvent(Component.java:4240)
    at java.awt.KeyboardFocusManager.redispatchEvent(KeyboardFocusManager.java:1848)
    at java.awt.DefaultKeyboardFocusManager.dispatchKeyEvent(DefaultKeyboardFocusManager.java:693)
    at java.awt.DefaultKeyboardFocusManager.preDispatchKeyEvent(DefaultKeyboardFocusManager.java:958)
    at java.awt.DefaultKeyboardFocusManager.typeAheadAssertions(DefaultKeyboardFocusManager.java:830)
    at java.awt.DefaultKeyboardFocusManager.dispatchEvent(DefaultKeyboardFocusManager.java:657)
    at java.awt.Component.dispatchEventImpl(Component.java:4282)
    at java.awt.Container.dispatchEventImpl(Container.java:2116)
    at java.awt.Window.dispatchEventImpl(Window.java:2429)
    at java.awt.Component.dispatchEvent(Component.java:4240)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:273)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:183)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:173)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:168)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:160)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:121)


** END NESTED EXCEPTION **



Last packet sent to the server was 2 ms ago.
    at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:2622)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:2916)
    at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1631)
    at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:1723)
    at com.mysql.jdbc.Connection.execSQL(Connection.java:3250)
    at com.mysql.jdbc.Connection.execSQL(Connection.java:3179)
    at com.mysql.jdbc.Statement.executeQuery(Statement.java:1207)
    at scm.DBControl.getResult(DBControl.java:49)
    at scm.new_fas.txtSearchKeyReleased(new_fas.java:1686)
    at scm.new_fas.access$2300(new_fas.java:28)
    at scm.new_fas$23.keyReleased(new_fas.java:1136)
    at java.awt.Component.processKeyEvent(Component.java:5999)
    at javax.swing.JComponent.processKeyEvent(JComponent.java:2794)
    at java.awt.Component.processEvent(Component.java:5815)
    at java.awt.Container.processEvent(Container.java:2058)
    at java.awt.Component.dispatchEventImpl(Component.java:4410)
    at java.awt.Container.dispatchEventImpl(Container.java:2116)
    at java.awt.Component.dispatchEvent(Component.java:4240)
    at java.awt.KeyboardFocusManager.redispatchEvent(KeyboardFocusManager.java:1848)
    at java.awt.DefaultKeyboardFocusManager.dispatchKeyEvent(DefaultKeyboardFocusManager.java:693)
    at java.awt.DefaultKeyboardFocusManager.preDispatchKeyEvent(DefaultKeyboardFocusManager.java:958)
    at java.awt.DefaultKeyboardFocusManager.typeAheadAssertions(DefaultKeyboardFocusManager.java:830)
    at java.awt.DefaultKeyboardFocusManager.dispatchEvent(DefaultKeyboardFocusManager.java:657)
    at java.awt.Component.dispatchEventImpl(Component.java:4282)
    at java.awt.Container.dispatchEventImpl(Container.java:2116)
    at java.awt.Window.dispatchEventImpl(Window.java:2429)
    at java.awt.Component.dispatchEvent(Component.java:4240)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:273)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:183)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:173)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:168)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:160)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:121)

有人可以帮我解决这个问题吗？我不明白怎么了!是服务器还是？ 非常感谢:)

这是我连接数据库的类(class):

package scm;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;

public class DBControl {

    private static DBControl con;
    private static String severIp = null;
    private static String severPort = null;
    private static String userName = null;
    private static String password = null;
    private static ResultSet rs = null;
    private static Connection cc = null;

    public DBControl() {
    }

    public static synchronized DBControl getInstance() {
        if (con == null) {
            con = new DBControl();
        }
        return con;
    }

    public void setSeverIp(String Ip) {
        severIp = Ip;
    }

    public void setSeverPort(String Port) {
        severPort = Port;
    }

    public void SetUserName(String Name) {
        userName = Name;
    }

    public void setPassword(String passWord) {
        password = passWord;
    }

    public static ResultSet getResult(String url) throws Exception {
        Statement s = cc.createStatement();
        rs = s.executeQuery(url);
        return rs;
    }

    public static Connection getConnection() throws Exception {
//        try {
        Class.forName("com.mysql.jdbc.Driver");
        cc = (Connection) DriverManager.getConnection("jdbc:mysql://" + getSeverIp() + ":" + getSeverPort() + "/anuradha_rr", getUserName(), getPassword());
        return cc;
    }

    public void setResult(String url) throws Exception {
        Class.forName("com.mysql.jdbc.Driver");
        cc = (Connection) DriverManager.getConnection("jdbc:mysql://" + getSeverIp() + ":" + getSeverPort() + "/anuradha_rr", getUserName(), getPassword());
        Statement s = (Statement) cc.createStatement();
        s.executeUpdate(url);
    }

    public static String getSeverIp() {
        return severIp;
    }

    public static String getSeverPort() {
        return severPort;
    }

    public static String getUserName() {
        return userName;
    }

    public static String getPassword() {
        return password;
    }
}

最佳答案

确保您没有使用失效的 jdbc 连接。根据您创建 jdbc 连接的方式，它们可能处于空闲状态。如果您反复使用同一个连接，请在尝试发出查询之前测试该连接，如果它已被 mysql 关闭，则获取一个新连接。

更新:

您在除 getResult() 之外的任何地方都创建了一个新连接，这是堆栈跟踪识别错误来源的地方。您可以像在其他地方一样创建新连接，也可以改进 getConnection() 的封装。换句话说，更改 getConnection() 以返回存储在您的类中的静态连接，条件是它不为空且仍然有效。否则创建一个新连接并返回它。

关于java - 访问远程服务器时 MySQL 连接出错，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/10048296/