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 Workbench 成功访问它。我将数据库添加到 Netbeans。当我尝试从 Netbeans 连接数据库时，出现此错误：

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.

我还尝试使用 RESTful Web 服务连接数据库。我收到此错误：

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_timeoutmysql变量：

SET wait_timeout=300;