mysqlservlet数据库
本来用jdbc能够好好的连上数据库的，但是就是重启了下机器，就根本连不上了，一开始怀疑是端口号的问题，但是更改了端口号依然报错，不知道为什么。 return drivermanager.getconnection(jdbc:mysql://localhost:8888/hello_db,root,123456);贴上错误信息，忘大牛指导！！
http://localhost:8080/severlethello/test/come
com.mysql.jdbc.exceptions.jdbc4.mysqlnontransientconnectionexception: communication link failure, message from server: can't get hostname for your address
at sun.reflect.nativeconstructoraccessorimpl.newinstance0(native method)
at sun.reflect.nativeconstructoraccessorimpl.newinstance(nativeconstructoraccessorimpl.java:62)
at sun.reflect.delegatingconstructoraccessorimpl.newinstance(delegatingconstructoraccessorimpl.java:45)
at java.lang.reflect.constructor.newinstance(constructor.java:422)
at com.mysql.jdbc.util.handlenewinstance(util.java:404)
at com.mysql.jdbc.util.getinstance(util.java:387)
at com.mysql.jdbc.sqlerror.createsqlexception(sqlerror.java:917)
at com.mysql.jdbc.sqlerror.createsqlexception(sqlerror.java:896)
at com.mysql.jdbc.sqlerror.createsqlexception(sqlerror.java:885)
at com.mysql.jdbc.mysqlio.dohandshake(mysqlio.java:1038)
at com.mysql.jdbc.connectionimpl.coreconnect(connectionimpl.java:2255)
at com.mysql.jdbc.connectionimpl.connectonetryonly(connectionimpl.java:2286)
at com.mysql.jdbc.connectionimpl.createnewio(connectionimpl.java:2085)
at com.mysql.jdbc.connectionimpl.(connectionimpl.java:795)
at com.mysql.jdbc.jdbc4connection.(jdbc4connection.java:44)
at sun.reflect.nativeconstructoraccessorimpl.newinstance0(native method)
at sun.reflect.nativeconstructoraccessorimpl.newinstance(nativeconstructoraccessorimpl.java:62)
at sun.reflect.delegatingconstructoraccessorimpl.newinstance(delegatingconstructoraccessorimpl.java:45)
at java.lang.reflect.constructor.newinstance(constructor.java:422)
at com.mysql.jdbc.util.handlenewinstance(util.java:404)
at com.mysql.jdbc.connectionimpl.getinstance(connectionimpl.java:400)
at com.mysql.jdbc.nonregisteringdriver.connect(nonregisteringdriver.java:327)
at java.sql.drivermanager.getconnection(drivermanager.java:664)
at java.sql.drivermanager.getconnection(drivermanager.java:247)
at com.david.jdbc.mysqljdbc.getconnection(mysqljdbc.java:12)
at com.david.testhello.testhello.doget(testhello.java:35)
at javax.servlet.http.httpservlet.service(httpservlet.java:624)
at javax.servlet.http.httpservlet.service(httpservlet.java:731)
at org.apache.catalina.core.applicationfilterchain.internaldofilter(applicationfilterchain.java:303)
at org.apache.catalina.core.applicationfilterchain.dofilter(applicationfilterchain.java:208)
at org.apache.tomcat.websocket.server.wsfilter.dofilter(wsfilter.java:52)
at org.apache.catalina.core.applicationfilterchain.internaldofilter(applicationfilterchain.java:241)
at org.apache.catalina.core.applicationfilterchain.dofilter(applicationfilterchain.java:208)
at org.apache.catalina.core.standardwrappervalve.invoke(standardwrappervalve.java:220)
at org.apache.catalina.core.standardcontextvalve.invoke(standardcontextvalve.java:122)
at org.apache.catalina.authenticator.authenticatorbase.invoke(authenticatorbase.java:505)
at org.apache.catalina.core.standardhostvalve.invoke(standardhostvalve.java:169)
at org.apache.catalina.valves.errorreportvalve.invoke(errorreportvalve.java:103)
at org.apache.catalina.valves.accesslogvalve.invoke(accesslogvalve.java:956)
at org.apache.catalina.core.standardenginevalve.invoke(standardenginevalve.java:116)
at org.apache.catalina.connector.coyoteadapter.service(coyoteadapter.java:423)
at org.apache.coyote.http11.abstracthttp11processor.process(abstracthttp11processor.java:1079)
at org.apache.coyote.abstractprotocol$abstractconnectionhandler.process(abstractprotocol.java:625)
at org.apache.tomcat.util.net.jioendpoint$socketprocessor.run(jioendpoint.java:316)
at java.util.concurrent.threadpoolexecutor.runworker(threadpoolexecutor.java:1142)
at java.util.concurrent.threadpoolexecutor$worker.run(threadpoolexecutor.java:617)
at org.apache.tomcat.util.threads.taskthread$wrappingrunnable.run(taskthread.java:61)
at java.lang.thread.run(thread.java:745)
connection closed!!!
二月 08, 2016 1:39:29 上午 org.apache.catalina.core.standardwrappervalve invoke
严重: servlet.service() for servlet [hello] in context with path [/severlethello] threw exception
java.lang.nullpointerexception
at com.david.testhello.testhello.doget(testhello.java:37)
at javax.servlet.http.httpservlet.service(httpservlet.java:624)
at javax.servlet.http.httpservlet.service(httpservlet.java:731)
at org.apache.catalina.core.applicationfilterchain.internaldofilter(applicationfilterchain.java:303)
at org.apache.catalina.core.applicationfilterchain.dofilter(applicationfilterchain.java:208)
at org.apache.tomcat.websocket.server.wsfilter.dofilter(wsfilter.java:52)
at org.apache.catalina.core.applicationfilterchain.internaldofilter(applicationfilterchain.java:241)
at org.apache.catalina.core.applicationfilterchain.dofilter(applicationfilterchain.java:208)
at org.apache.catalina.core.standardwrappervalve.invoke(standardwrappervalve.java:220)
at org.apache.catalina.core.standardcontextvalve.invoke(standardcontextvalve.java:122)
at org.apache.catalina.authenticator.authenticatorbase.invoke(authenticatorbase.java:505)
at org.apache.catalina.core.standardhostvalve.invoke(standardhostvalve.java:169)
at org.apache.catalina.valves.errorreportvalve.invoke(errorreportvalve.java:103)
at org.apache.catalina.valves.accesslogvalve.invoke(accesslogvalve.java:956)
at org.apache.catalina.core.standardenginevalve.invoke(standardenginevalve.java:116)
at org.apache.catalina.connector.coyoteadapter.service(coyoteadapter.java:423)
at org.apache.coyote.http11.abstracthttp11processor.process(abstracthttp11processor.java:1079)
at org.apache.coyote.abstractprotocol$abstractconnectionhandler.process(abstractprotocol.java:625)
at org.apache.tomcat.util.net.jioendpoint$socketprocessor.run(jioendpoint.java:316)
at java.util.concurrent.threadpoolexecutor.runworker(threadpoolexecutor.java:1142)
at java.util.concurrent.threadpoolexecutor$worker.run(threadpoolexecutor.java:617)
at org.apache.tomcat.util.threads.taskthread$wrappingrunnable.run(taskthread.java:61)
at java.lang.thread.run(thread.java:745)