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：
1 Success loading Mysql Driver!
2 com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link f
3 lure
4
5 The last packet sent successfully to the server was 0 milliseconds ago. The dr
6 er has not received any packets from the server.
7 at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Metho
8
9 at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstru
10 orAccessorImpl.java:39)
11 at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Delegatin
12 onstructorAccessorImpl.java:27)
13 at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
14 at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
15 at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java
16 121)
17 at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:357)
18 at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2482)
19 at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java
20 519)
21 at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2304)
22 at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:834)
23 at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:47)
24 at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Metho
25
26 at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstru
27 orAccessorImpl.java:39)
28 at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Delegatin
29 onstructorAccessorImpl.java:27)
30 at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
31 at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
32 at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:416)
33 at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.ja
34 :346)
35 at java.sql.DriverManager.getConnection(DriverManager.java:582)
36 at java.sql.DriverManager.getConnection(DriverManager.java:185)
37 at ReadAndWriteData_use.getConnection(ReadAndWriteData_use.java:71)
38 at ReadAndWriteData_use.ConnectMysql(ReadAndWriteData_use.java:46)
39 at ReadAndWriteData_use.main(ReadAndWriteData_use.java:212)
40 Caused by: java.net.ConnectException: Connection refused: connect
41 at java.net.PlainSocketImpl.socketConnect(Native Method)
42 at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:333)
43 at java.net.PlainSocketImpl.connectToAddress(PlainSocketImpl.java:195)
44 at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:182)
45 at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:366)
46 at java.net.Socket.connect(Socket.java:529)
47 at java.net.Socket.connect(Socket.java:478)
48 at java.net.Socket.<init>(Socket.java:375)
49 at java.net.Socket.<init>(Socket.java:218)
50 at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.
51 va:259)
52 at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:307)
53 ... 17 more
54 Success connect Mysql server!
55 get data error!java.lang.NullPointerException
56 at ReadAndWriteData_use.ConnectMysql(ReadAndWriteData_use.java:49)
57 at ReadAndWriteData_use.main(ReadAndWriteData_use.java:212)
58 开始........
59 com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link f
60 lure
61
62 The last packet sent successfully to the server was 0 milliseconds ago. The dr
63 er has not received any packets from the server.
64 at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Metho
65
66 at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstru
67 orAccessorImpl.java:39)
68 at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Delegatin
69 onstructorAccessorImpl.java:27)
70 at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
71 at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
72 at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java
73 121)
74 at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:357)
75 at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2482)
76 at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java
77 519)
78 at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2304)
79 at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:834)
80 at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:47)
81 at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Metho
82
83 at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstru
84 orAccessorImpl.java:39)
85 at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Delegatin
86 onstructorAccessorImpl.java:27)
87 at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
88 at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
89 at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:416)
90 at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.ja
91 :346)
92 at java.sql.DriverManager.getConnection(DriverManager.java:582)
93 at java.sql.DriverManager.getConnection(DriverManager.java:185)
94 at ReadAndWriteData_use.getConnection(ReadAndWriteData_use.java:71)
95 at ReadAndWriteData_use.readFile(ReadAndWriteData_use.java:105)
96 at ReadAndWriteData_use.main(ReadAndWriteData_use.java:218)
97 Caused by: java.net.ConnectException: Connection refused: connect
98 at java.net.PlainSocketImpl.socketConnect(Native Method)
99 at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:333)
100 at java.net.PlainSocketImpl.connectToAddress(PlainSocketImpl.java:195)
101 at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:182)
102 at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:366)
103 at java.net.Socket.connect(Socket.java:529)
104 at java.net.Socket.connect(Socket.java:478)
105 at java.net.Socket.<init>(Socket.java:375)
106 at java.net.Socket.<init>(Socket.java:218)
107 at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.
108 va:259)
109 at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:307)
110 ... 17 more
111 step1:getConnection() -> success!
112 Exception in thread "main" java.lang.NullPointerException
113 at ReadAndWriteData_use.readFile(ReadAndWriteData_use.java:107)
114 at ReadAndWriteData_use.main(ReadAndWriteData_use.java:218)
115 Success loading Mysql Driver!
时间： 2024-07-31 14:25:50