我使用一个.jar的文件，想在cmd中以“java -jar *.jar”的格式运行，方便system.println()一些信息，该jar包中包含数据库连接内容，在我关闭comodo防火墙和windows防火墙的情况下，该文件无法运行，在我开启comodo防火墙时，会提示是否连接internet(实际上是127.0.0.1的本地连接)，点击同意可正常连接。坑爹的是，我只开启windows防火墙而不开启comodo，系统无任何提示，不能运行此程序，真心不知道是被哪个防火墙拦截的。
另外，如果点击同意之后，后续运行相同程序没有问题会可以继续运行，但是更新之后便必须开启comodo重新同意才可以在cmd中运行该jar包，因此调查一下不开启comodo而jar包被拦截到底是什么原因。
附录：等一段时间后，cmd弹出异常提示如下：
Success loading Mysql Driver!
com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link f
lure The last packet sent successfully to the server was 0 milliseconds ago. The dr
er has not received any packets from the server.
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Metho at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstru
orAccessorImpl.java:39)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Delegatin
onstructorAccessorImpl.java:27)
at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java
121)
at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:357)
at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2482)
at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java
519)
at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2304)
at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:834)
at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:47)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Metho at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstru
orAccessorImpl.java:39)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Delegatin
onstructorAccessorImpl.java:27)
at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:416)
at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.ja
:346)
at java.sql.DriverManager.getConnection(DriverManager.java:582)
at java.sql.DriverManager.getConnection(DriverManager.java:185)
at ReadAndWriteData_use.getConnection(ReadAndWriteData_use.java:71)
at ReadAndWriteData_use.ConnectMysql(ReadAndWriteData_use.java:46)
at ReadAndWriteData_use.main(ReadAndWriteData_use.java:212)
Caused by: java.net.ConnectException: Connection refused: connect
at java.net.PlainSocketImpl.socketConnect(Native Method)
at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:333)
at java.net.PlainSocketImpl.connectToAddress(PlainSocketImpl.java:195)
at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:182)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:366)
at java.net.Socket.connect(Socket.java:529)
at java.net.Socket.connect(Socket.java:478)
at java.net.Socket.<init>(Socket.java:375)
at java.net.Socket.<init>(Socket.java:218)
at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.
va:259)
at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:307)
... 17 more
Success connect Mysql server!
get data error!java.lang.NullPointerException
at ReadAndWriteData_use.ConnectMysql(ReadAndWriteData_use.java:49)
at ReadAndWriteData_use.main(ReadAndWriteData_use.java:212)
开始........
com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link f
lure The last packet sent successfully to the server was 0 milliseconds ago. The dr
er has not received any packets from the server.
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Metho at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstru
orAccessorImpl.java:39)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Delegatin
onstructorAccessorImpl.java:27)
at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java
121)
at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:357)
at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2482)
at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java
519)
at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2304)
at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:834)
at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:47)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Metho at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstru
orAccessorImpl.java:39)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Delegatin
onstructorAccessorImpl.java:27)
at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:416)
at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.ja
:346)
at java.sql.DriverManager.getConnection(DriverManager.java:582)
at java.sql.DriverManager.getConnection(DriverManager.java:185)
at ReadAndWriteData_use.getConnection(ReadAndWriteData_use.java:71)
at ReadAndWriteData_use.readFile(ReadAndWriteData_use.java:105)
at ReadAndWriteData_use.main(ReadAndWriteData_use.java:218)
Caused by: java.net.ConnectException: Connection refused: connect
at java.net.PlainSocketImpl.socketConnect(Native Method)
at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:333)
at java.net.PlainSocketImpl.connectToAddress(PlainSocketImpl.java:195)
at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:182)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:366)
at java.net.Socket.connect(Socket.java:529)
at java.net.Socket.connect(Socket.java:478)
at java.net.Socket.<init>(Socket.java:375)
at java.net.Socket.<init>(Socket.java:218)
at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.
va:259)
at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:307)
... 17 more
step1:getConnection() -> success!
Exception in thread "main" java.lang.NullPointerException
at ReadAndWriteData_use.readFile(ReadAndWriteData_use.java:107)
at ReadAndWriteData_use.main(ReadAndWriteData_use.java:218)
Success loading Mysql Driver!