抓狂，这个错误怎么解决

Question

com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

Last packet sent to the server was 0 ms ago.

at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)

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

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

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:1074)

at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2104)

at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:729)

at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:46)

at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)

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

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

at java.lang.reflect.Constructor.newInstance(Unknown Source)

at com.mysql.jdbc.Util.handleNewInstance(Util.java:406)

at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:302)

at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:283)

at java.sql.DriverManager.getConnection(Unknown Source)

at java.sql.DriverManager.getConnection(Unknown Source)

at JDBCUtlTool.getConnection(JDBCUtlTool.java:17)

at JDBCUtlTool.main(JDBCUtlTool.java:55)

Caused by: java.net.UnknownHostException: localhost_3306

at java.net.Inet6AddressImpl.lookupAllHostAddr(Native Method)

at java.net.InetAddress$1.lookupAllHostAddr(Unknown Source)

at java.net.InetAddress.getAddressesFromNameService(Unknown Source)

at java.net.InetAddress.getAllByName0(Unknown Source)

at java.net.InetAddress.getAllByName(Unknown Source)

at java.net.InetAddress.getAllByName(Unknown Source)

at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.java:246)

at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:276)

at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2027)

... 13 more

Exception in thread "main" java.lang.NullPointerException

at JDBCUtlTool.main(JDBCUtlTool.java:57)

Answer 1

不应该是localhost_3306吧，应该是localhost:3306