针对连接丢失的Java应用程序处理

Question

由于连接丢失（我认为是问题所在），因此我的应用程序似乎挂了一夜。如何构造我的应用程序，以便它可以尝试卷起新的连接？

** BEGIN NESTED EXCEPTION ** 

com.mysql.jdbc.exceptions.jdbc4.CommunicationsException 
MESSAGE: The last packet successfully received from the server was54521 seconds 
ago.The last packet sent successfully to the server was 54521 seconds ago, which 
    is longer than the server configured value of 'wait_timeout'. You should consi 
der either expiring and/or testing connection validity before use in your applic 
ation, increasing the server configured values for client timeouts, or using the 
Connector/J connection property 'autoReconnect=true' to avoid this problem. 

STACKTRACE: 

com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: The last packet success 
fully received from the server was54521 seconds ago.The last packet sent success 
fully to the server was 54521 seconds ago, which is longer than the server conf 
igured value of 'wait_timeout'. You should consider either expiring and/or testi 
ng connection validity before use in your application, increasing the server con 
figured values for client timeouts, or using the Connector/J connection property 
'autoReconnect=true' to avoid this problem. 
     at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) 

     at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source) 

     at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Sou 
rce) 
     at java.lang.reflect.Constructor.newInstance(Unknown Source) 
     at com.mysql.jdbc.Util.handleNewInstance(Util.java:406) 
     at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1 
074) 
     at com.mysql.jdbc.MysqlIO.send(MysqlIO.java:3246) 
     at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1917) 
     at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2060) 
     at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2536) 
     at com.mysql.jdbc.ConnectionImpl.setCatalog(ConnectionImpl.java:4962) 
     at com.mysql.jdbc.DatabaseMetaData.getCallStmtParameterTypes(DatabaseMet 
aData.java:1506) 
     at com.mysql.jdbc.DatabaseMetaData.getProcedureOrFunctionColumns(Databas 
eMetaData.java:4120) 
     at com.mysql.jdbc.DatabaseMetaData.getProcedureColumns(DatabaseMetaData. 
java:4057) 
     at com.mysql.jdbc.CallableStatement.determineParameterTypes(CallableStat 
ement.java:809) 
     at com.mysql.jdbc.CallableStatement.<init>(CallableStatement.java:609) 
     at com.mysql.jdbc.JDBC4CallableStatement.<init>(JDBC4CallableStatement.j 
ava:46) 
     at sun.reflect.GeneratedConstructorAccessor6.newInstance(Unknown Source) 

     at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Sou 
rce) 
     at java.lang.reflect.Constructor.newInstance(Unknown Source) 
     at com.mysql.jdbc.Util.handleNewInstance(Util.java:406) 
     at com.mysql.jdbc.CallableStatement.getInstance(CallableStatement.java:5 
05) 
     at com.mysql.jdbc.ConnectionImpl.parseCallableStatement(ConnectionImpl.j 
ava:3881) 
     at com.mysql.jdbc.ConnectionImpl.prepareCall(ConnectionImpl.java:3965) 
     at com.mysql.jdbc.ConnectionImpl.prepareCall(ConnectionImpl.java:3939) 
     at com.protocase.hmiclient.db.HMIDatabaseAdapter.getAvailableBatchesForW 
orkstation(HMIDatabaseAdapter.java:471) 
     at com.protocase.hmiclient.views.WorkstationContainer.getBatches(Worksta 
tionContainer.java:74) 
     at com.protocase.hmiclient.views.BatchList.<init>(BatchList.java:55) 
     at com.protocase.hmiclient.views.WorkstationContainer.goToBatchList(Work 
stationContainer.java:56) 
     at com.protocase.hmiclient.views.forms.BatchListControlPanel.refreshButt 
onActionPerformed(BatchListControlPanel.java:118) 
     at com.protocase.hmiclient.views.forms.BatchListControlPanel.access$200(
BatchListControlPanel.java:16) 
     at com.protocase.hmiclient.views.forms.BatchListControlPanel$3.actionPer 
formed(BatchListControlPanel.java:64) 
     at javax.swing.AbstractButton.fireActionPerformed(Unknown Source) 
     at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source) 
     at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source) 
     at javax.swing.DefaultButtonModel.setPressed(Unknown Source) 
     at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Sour 
ce) 
     at java.awt.Component.processMouseEvent(Unknown Source) 
     at javax.swing.JComponent.processMouseEvent(Unknown Source) 
     at java.awt.Component.processEvent(Unknown Source) 
     at java.awt.Container.processEvent(Unknown Source) 
     at java.awt.Component.dispatchEventImpl(Unknown Source) 
     at java.awt.Container.dispatchEventImpl(Unknown Source) 
     at java.awt.Component.dispatchEvent(Unknown Source) 
     at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source) 
     at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source) 
     at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source) 
     at java.awt.Container.dispatchEventImpl(Unknown Source) 
     at java.awt.Window.dispatchEventImpl(Unknown Source) 
     at java.awt.Component.dispatchEvent(Unknown Source) 
     at java.awt.EventQueue.dispatchEventImpl(Unknown Source) 
     at java.awt.EventQueue.access$000(Unknown Source) 
     at java.awt.EventQueue$1.run(Unknown Source) 
     at java.awt.EventQueue$1.run(Unknown Source) 
     at java.security.AccessController.doPrivileged(Native Method) 
     at java.security.AccessControlContext$1.doIntersectionPrivilege(Unknown 
Source) 
     at java.security.AccessControlContext$1.doIntersectionPrivilege(Unknown 
Source) 
     at java.awt.EventQueue$2.run(Unknown Source) 
     at java.awt.EventQueue$2.run(Unknown Source) 
     at java.security.AccessController.doPrivileged(Native Method) 
     at java.security.AccessControlContext$1.doIntersectionPrivilege(Unknown 
Source) 
     at java.awt.EventQueue.dispatchEvent(Unknown Source) 
     at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source) 
     at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source) 
     at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source) 
     at java.awt.EventDispatchThread.pumpEvents(Unknown Source) 
     at java.awt.EventDispatchThread.pumpEvents(Unknown Source) 
     at java.awt.EventDispatchThread.run(Unknown Source) 
Caused by: java.net.SocketException: Software caused connection abort: socket wr 
ite error 
     at java.net.SocketOutputStream.socketWrite0(Native Method) 
     at java.net.SocketOutputStream.socketWrite(Unknown Source) 
     at java.net.SocketOutputStream.write(Unknown Source) 
     at java.io.BufferedOutputStream.flushBuffer(Unknown Source) 
     at java.io.BufferedOutputStream.flush(Unknown Source) 
     at com.mysql.jdbc.MysqlIO.send(MysqlIO.java:3227) 
     ... 61 more 


** END NESTED EXCEPTION ** 

Answer 1

此异常提示你打开了：

事件发生以来我已经更新我的应用程序使用的，因此getConnection（）方法：

private Connection getConnection() { 
    boolean failed = false; 
    try{ 
     failed = !connection.isValid(1000); 
    }catch(SQLException ex){ 
     System.out.println("WARNING: Connection not valid!"); 
    } 
    try{ 
     failed = connection.isClosed(); 
    }catch(SQLException ex){ 
     System.out.println("WARNING: Connection is closed!"); 
    } 
    if(failed){ 
     System.out.println("Renewing connection"); 
     this.initializeConnection(); 
    } 
    return connection; 
} 

这是输出仅在应用程序启动期间连接一次，并在应用程序的生命周期中保持永久打开。这不好。数据库迟早会收回连接，因为它已打开太久。在打开它并在其上执行查询时，应该在同一个try块的finally块中正确关闭连接。

E.g.

public Entity find(Long id) throws SQLException { 
    Connection connection = null; 
    // ... 

    try { 
     connection = database.getConnection(); 
     // ... 
    } finally { 
     // ... 
     if (connection != null) try { connection.close(); } catch (SQLException logOrIgnore) {} 
    } 

    return entity; 
} 

如果你有关于这个性能问题（这是因为连接是最昂贵的任务非常合理的），那么你就应该使用连接池。它也透明地处理了这种“连接丢失”问题。例如，BoneCP。请注意，在连接池的情况下，您仍应按照上面的JDBC代码惯例关闭finally块中的连接。它将使它们可供重用。