我在网络服务器中托管了一个MySQL数据库。我授予所有权限并允许我的IP从本地计算机远程连接到此数据库。它连接起来，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，而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。我不明白什么是错的！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;
}
}
答案 0 :(得分：3)
确保您没有使用死jdbc连接。根据您创建jdbc连接的方式，它们可能会空闲。如果您反复使用相同的连接，请在尝试发出查询之前测试连接，如果mysql已关闭它，请获取新连接。
更新：
除了getResult（）之外，您可以在任何地方创建新连接，这是堆栈跟踪标识错误的地方。您可以像在其他任何地方一样创建新连接，或者改进getConnection（）的封装。换句话说，更改getConnection（）以返回存储在类中的静态Connection，条件是它不为null且仍然有效。否则创建一个新连接并返回该连接。
答案 1 :(得分：2)
这在MySQL中是一个相当普遍的问题，不幸的是，只有在生产中，当应用程序运行一段延长的时间时，通常只会在短暂的开发周期中发生。
MySQL在没有通知其客户端的情况下关闭连接，并且当您尝试使用超时连接时出现的不太明显的异常。例如，您可以定期ping一些简单的SQL语句，以避免超时。
最好使用连接池（以避免有太多用户同时访问数据库的问题），例如一般而言，DBCP。 DBCP可以轻松添加到您的应用程序中，您只需将其设置为准JDBC驱动程序。 你可以在那里设置正确的方式。
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'
<强>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新连接。