3

我在网络服务器中托管了一个 MySQL 数据库。我已授予所有权限并允许我的 IP从本地计算机远程连接到该数据库。它已连接，我能够将数据从数据库检索到我的 Java Swing 应用程序。但是，有时我会收到此错误消息，并且与托管数据库的连接失败。 错误如下图所示：

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种情况。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课程：

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;
    }
}
4

2 回答 2

3

确保您没有使用死的 jdbc 连接。根据您创建 jdbc 连接的方式，它们可能会处于空闲状态。如果您一遍又一遍地使用相同的连接，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() 之外的任何地方创建一个新连接，这是堆栈跟踪标识错误的来源。您可以像在其他任何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 Connection，条件是它不为 null 并且仍然有效。否则创建一个新连接并返回它。

于 2012-04-06T19:39:15.157 回答
2

这是 MySQL 中相当常见的问题，不幸的是，通常仅在应用程序运行一段时间后才会在生产中发生，这与较短的开发周期不同。

MySQL 在不通知其客户端的情况下关闭连接，当您尝试使用超时连接时出现的异常并不明显。例如，您可以定期使用一些简单的 SQL 语句 ping 连接以避免超时。

一般而言，使用连接池（以避免太多用户同时访问数据库的问题）是一种很好的做法，例如 DBCP。DBCP 可以很容易地添加到您的应用程序中，您只需将其设置为准 JDBC 驱动程序。在那里你可以正确地设置东西。

我从我的一个项目中复制了这个 DBCP 配置：

                 MaxActive=20,
                 MaxWait=60000,
                 TestWhileIdle=true,
                 TimeBetweenEvictionRunsMillis=300000,
                 MinEvictableIdleTimeMillis=300000,
                 TestOnBorrow=true,
                 ValidationQuery='SELECT 1'

更新： 作为一个非常简单的解决方案，您可以尝试在访问时捕获异常并在这种情况下打开一个新连接。

于 2012-04-06T21:45:35.700 回答