我有个问题：
我有一个在Ubuntu 12.04操作系统的远程服务器上的虚拟机上运行的Web服务。
现在，我想testing这个Web服务，并使用我在Web服务客户端中开发的代码：
public class Client3 { public static void main(String[] args) { byte[] inputFile; String nomeFile; String jdbcURL = "jdbc:mysql://xxx.xxx.xxx.xxx:3306/mydb"; String username = "root"; String password = "xxx"; String driver = "com.mysql.jdbc.Driver"; String result = wsmethod(jdbcURL, username, password, driver); private static String wsmethod(java.lang.String jdbcURL, java.lang.String username, java.lang.String password, java.lang.String driver) { ws.myWs_Service service = new ws.myWs_Service(); ws.myWs port = service.getmyWsPort(); return port.wsmethod(jdbcURL, username, password, driver); } } 此代码想要select连接信息到数据库并将其提供给我的Web服务。 然后，我的Web服务将使用D2RQ库将数据库中的信息转换为RDF。 我的Web服务客户端是使用虚拟机的IP地址创build的。
当我运行这个代码时，我得到这个错误：
Exception in thread "main" javax.xml.ws.soap.SOAPFaultException: Database connection to jdbc:mysql://xxx.xxx.xxx.xxx:3306/mydb failed (user: root): 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. (E54) at com.sun.xml.internal.ws.fault.SOAP11Fault.getProtocolException(SOAP11Fault.java:178) at com.sun.xml.internal.ws.fault.SOAPFaultBuilder.createException(SOAPFaultBuilder.java:125) at com.sun.xml.internal.ws.client.sei.SyncMethodHandler.invoke(SyncMethodHandler.java:108) at com.sun.xml.internal.ws.client.sei.SyncMethodHandler.invoke(SyncMethodHandler.java:78) at com.sun.xml.internal.ws.client.sei.SEIStub.invoke(SEIStub.java:135) at com.sun.proxy.$Proxy31.wsmethod(Unknown Source) at client3.Client3.wsmethod(Client3.java:77) at client3.Client3.main(Client3.java:70) Caused by: de.fuberlin.wiwiss.d2rq.D2RQException: Database connection to jdbc:mysql://xxx.xxx.xxx.xxx:3306/mydb failed (user: root): 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. (E54) at de.fuberlin.wiwiss.d2rq.sql.ConnectedDB.connect(ConnectedDB.java:201) at de.fuberlin.wiwiss.d2rq.sql.ConnectedDB.connection(ConnectedDB.java:170) at de.fuberlin.wiwiss.d2rq.dbschema.DatabaseSchemaInspector.<init>(DatabaseSchemaInspector.java:45) at de.fuberlin.wiwiss.d2rq.sql.ConnectedDB.schemaInspector(ConnectedDB.java:243) at de.fuberlin.wiwiss.d2rq.mapgen.MappingGenerator.<init>(MappingGenerator.java:77) at de.fuberlin.wiwiss.d2rq.SystemLoader.openMappingGenerator(SystemLoader.java:224) at Prova.classprova.methodprova(classprova.java:70) at WS.SmartHealth_ws.wsmethod(myWs.java:249) at sun.reflect.GeneratedMethodAccessor63.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:606) at com.sun.xml.ws.api.server.InstanceResolver$1.invoke(InstanceResolver.java:246) at com.sun.xml.ws.server.InvokerTube$2.invoke(InvokerTube.java:146) at com.sun.xml.ws.server.sei.EndpointMethodHandler.invoke(EndpointMethodHandler.java:257) at com.sun.xml.ws.server.sei.SEIInvokerTube.processRequest(SEIInvokerTube.java:95) at com.sun.xml.ws.api.pipe.Fiber.__doRun(Fiber.java:629) at com.sun.xml.ws.api.pipe.Fiber._doRun(Fiber.java:588) at com.sun.xml.ws.api.pipe.Fiber.doRun(Fiber.java:573) at com.sun.xml.ws.api.pipe.Fiber.runSync(Fiber.java:470) at com.sun.xml.ws.server.WSEndpointImpl$2.process(WSEndpointImpl.java:295) at com.sun.xml.ws.transport.http.HttpAdapter$HttpToolkit.handle(HttpAdapter.java:515) at com.sun.xml.ws.transport.http.HttpAdapter.handle(HttpAdapter.java:285) at com.sun.xml.ws.transport.http.servlet.ServletAdapter.handle(ServletAdapter.java:143) at com.sun.xml.ws.transport.http.servlet.WSServletDelegate.doGet(WSServletDelegate.java:155) at com.sun.xml.ws.transport.http.servlet.WSServletDelegate.doPost(WSServletDelegate.java:189) at com.sun.xml.ws.transport.http.servlet.WSServlet.doPost(WSServlet.java:76) at javax.servlet.http.HttpServlet.service(HttpServlet.java:644) at javax.servlet.http.HttpServlet.service(HttpServlet.java:725) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106) at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:506) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:142) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79) at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:610) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:537) at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1081) at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:658) at org.apache.coyote.http11.Http11NioProtocol$Http11ConnectionHandler.process(Http11NioProtocol.java:222) at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1566) at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1523) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615) at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) at java.lang.Thread.run(Thread.java:745) Java Result: 1
如果我在本地运行这个代码，我不会得到这个错误。 实际上，如果我在本地机器上使用Web服务的IP地址创build我的Web服务客户端，我不会收到这个错误。 为什么我得到这个错误？
我已经尝试从虚拟机到mysql主机，我得到“目标主机无法访问”。 为什么？