我无法从Netbeans连接数据库

Question

我在互联网上有一个MySQL数据库。我可以通过浏览器和MySQL工作台成功访问它。我给Netbeans添加了数据库。当我试图从Netbeans连接数据库时，我得到这个错误:

com.mysql.jdbc.exceptions.jdbc4.CommunicationsException
Error code 0, SQL state 08S01: Communications link failure
The last packet successfully received from the server was 14.047 milliseconds ago.  The last packet sent successfully to the server was 1 milliseconds ago.

我也尝试使用restful web服务连接数据库。我得到这个错误:

GET RequestFailed RequestFailed --> Status: (500) 
Response: {
HTTP Status 500 -
type Exception report
message
descriptionThe server encountered an internal error () that prevented it from fulfilling this request.
exception
javax.servlet.ServletException: Exception [EclipseLink-4002] (Eclipse Persistence Services - 2.3.2.v20111125-r10461): org.eclipse.persistence.exceptions.DatabaseException
Internal Exception: com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: No operations allowed after connection closed.
Error Code: 0
Call: SELECT o_id, isim, not, yas FROM ogrenci
Query: ReadAllQuery(referenceClass=Ogrenci sql="SELECT o_id, isim, not, yas FROM ogrenci")
root cause
Exception [EclipseLink-4002] (Eclipse Persistence Services - 2.3.2.v20111125-r10461): org.eclipse.persistence.exceptions.DatabaseException
Internal Exception: com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: No operations allowed after connection closed.
Error Code: 0
Call: SELECT o_id, isim, not, yas FROM ogrenci
Query: ReadAllQuery(referenceClass=Ogrenci sql="SELECT o_id, isim, not, yas FROM ogrenci")
root cause
com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: No operations allowed after connection closed.
root cause
com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
The last packet successfully received from the server was 228.471 milliseconds ago.  The last packet sent successfully to the server was 11 milliseconds ago.
root cause
java.io.EOFException: Can not read response from server. Expected to read 4 bytes, read 0 bytes before connection was unexpectedly lost.
note The full stack traces of the exception and its root causes are available in the GlassFish Server Open Source Edition 3.1.2.2 logs.

Answer 1

尝试增加wait_timeout mysql变量:

SET wait_timeout=300;