如何连接到从applet的SQL数据库 [英] How to connect to SQL database from applet
问题描述
我正在连接到存储在同一个Web服务器上的数据库的小程序，当我在Eclipse中的小程序查看器测试code，它连接。问题是，当我尝试的Eclipse之外运行它（网络服务器或本地的），我得到这个错误：
I am making an applet that connects to a database that is stored on the same web server, and when I test the code in the applet viewer in Eclipse, it connects. Problem is, when I try to run it outside Eclipse (on web server or locally), I get this error:
Exception in thread "AWT-EventQueue-2" java.lang.ExceptionInInitializerError
at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:286)
at java.sql.DriverManager.getConnection(Unknown Source)
at java.sql.DriverManager.getConnection(Unknown Source)
at com.j_ctrl.MovePanel.connectDB(MovePanel.java:569)
at com.j_ctrl.MovePanel.showHighScore(MovePanel.java:558)
at com.j_ctrl.MovePanel.enterPress(MovePanel.java:544)
at com.j_ctrl.MovePanel$1.keyPressed(MovePanel.java:163)
at java.awt.Component.processKeyEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.KeyboardFocusManager.redispatchEvent(Unknown Source)
at java.awt.DefaultKeyboardFocusManager.dispatchKeyEvent(Unknown Source)
at java.awt.DefaultKeyboardFocusManager.preDispatchKeyEvent(Unknown Source)
at java.awt.DefaultKeyboardFocusManager.typeAheadAssertions(Unknown Source)
at java.awt.DefaultKeyboardFocusManager.dispatchEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$000(Unknown Source)
at java.awt.EventQueue$1.run(Unknown Source)
at java.awt.EventQueue$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(Unknown Source)
at java.security.AccessControlContext$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue$2.run(Unknown Source)
at java.awt.EventQueue$2.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)
Caused by: java.security.AccessControlException: access denied (java.util.PropertyPermission file.encoding read)
at java.security.AccessControlContext.checkPermission(Unknown Source)
at java.security.AccessController.checkPermission(Unknown Source)
at java.lang.SecurityManager.checkPermission(Unknown Source)
at java.lang.SecurityManager.checkPropertyAccess(Unknown Source)
at java.lang.System.getProperty(Unknown Source)
at com.mysql.jdbc.StringUtils.<clinit>(StringUtils.java:70)
... 39 more
有什么特别需要为了从一个小程序连接到SQL数据库做？
这里是code处理的连接：
Is there anything special that needs to be done in order to connect to an SQL database from an applet? Here is the code that handles the connection:
private void connectDB(){
try{
String driverName = "com.mysql.jdbc.Driver";
Class.forName(driverName);
String url = "jdbc:mysql://localhost/database";
String user = "user";
String pass = "pass";
connection = DriverManager.getConnection(url, user, pass);
System.out.println("Connected");
}catch(Exception ex){
ex.printStackTrace();
}
}
我改了用户名，密码和数据库在这里，但在我的code正确。
I changed the username, password and database here, but in my code they are correct.
修改
由于连接到SQL服务器没有工作（我想它托管在其他主机上），我已经结束了改变我访问数据库的方式。小程序打开主机，这反过来又连接到数据库上的PHP文件的连接。无论哪种方式，这是更安全的。
Since connecting to the SQL server didn't work (I imagine it was hosted on a different host), I have ended up changing the way I access the database. The applet opens a connection to a PHP file on the host, which in turn connects to the database. Either way this is more secure.
推荐答案
这是由用于小应用程序的安全模型造成的。这里有一个很好的文章总结了解决此问题的方式主要有两种 - 要么签署applet或使用策略文件。让我们知道，如果你还在试图其中之一后遇到的问题：
This is being caused by the security model for applets. Here's a good article summarizing the two main ways around this issue - either sign the applet or use a policy file. Let us know if you still experience problems after trying one of these:
的http://www.$c$cranch.com/how-to/java/HowCanAnAppletReadFilesOnTheLocalFileSystem
这篇关于如何连接到从applet的SQL数据库的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
