Cannot get a connection, general error

当出现上述报错时，请继续查看本文

	private static Connection connection = null;
	private static PreparedStatement preStmt = null;
	private static ResultSet result = null;

private static Connection getConnection() throws NamingException, SQLException {
		Context context = new InitialContext();
		DataSource ds = (DataSource)context.lookup("java:comp/env/MySQL");
		return ds.getConnection();
	}

private static PreparedStatement createPrepareStatement(String sql, Object[] params) throws ClassNotFoundException, SQLException, NamingException {
		PreparedStatement preStmt = null;
		preStmt = getConnection().prepareStatement(sql);
		if (params != null) {
			for (int i = 0; i < params.length; i++) {
				preStmt.setObject(i + 1, params[i]);
			}
		}
		return preStmt;
	}

private static void closeAll(ResultSet rs, Statement stmt, Connection connection) {
		try {
			if (rs != null)
				rs.close();
			if (stmt != null)
				stmt.close();
			if (connection != null) 
				connection.close();
		} catch (SQLException e) {
			e.printStackTrace();
		}
	}

经仔细阅读发现，getConnection生成的Connection没有给connection变量，导致closeAll中的if (connection!=null)始终处于不执行的状态，connection.close()一直没有执行。多次获取Connection，使得connection不能再被获取。