java.security.AccessControlException: access denie

Exception: Cannot load connection class because
of underlying exception:
'java.security.AccessControlException: access denied (java.lang.RuntimePermission modifyThreadGroup)'.


gwt 1.6 新建一个工程使用jdbc连接的时候有问题.

报的这个错误.

1.在run-> web application
的时候在helloworld里面写一段jdbc连接的代码

@SuppressWarnings("serial")
public class GreetingServiceImpl extends RemoteServiceServlet implements
		GreetingService {

	public String greetServer(String input) {
		String serverInfo = getServletContext().getServerInfo();
		String userAgent = getThreadLocalRequest().getHeader("User-Agent");

		Connection con = null;
		try {
			Class.forName("com.mysql.jdbc.Driver").newInstance();
			String url = "jdbc:mysql://localhost:3306/test_ssh?autoReconnect=true&useUnicode=true&characterEncoding=utf-8";
			con = DriverManager.getConnection(url, "root", "");
			if (!con.isClosed())
				System.out.println("Successfully connected to "
						+ "MySQL server using TCP/IP...");

		} catch (Exception e) {
			System.err.println("Exception: " + e.getMessage());
		} finally {
			try {
				if (con != null)
					con.close();
			} catch (SQLException e) {
			}
		}

		return "Hello, " + input + "!<br><br>I am running " + serverInfo
				+ ".<br><br>It looks like you are using:<br>" + userAgent;
	}
}

2.用 run-> web application的时候报错误.

Exception: Cannot load connection class because 
of underlying exception: 
'java.security.AccessControlException: access denied (java.lang.RuntimePermission modifyThreadGroup)'.

在属性里面添加jar包就好了.