servlet生命周期--3

3.3 需要同步的资源
                        成员变量,静态变量,数据库连接,网络资源,文件等.
        4. service的销毁--destroy()
                当服务器决定销毁servlet时,就会调用这个方法,一般我们在这个方法中作一些于inti()相反的工作,例如释放数据库的连接,文件的关闭,终止后台进程等工作.
                还有,当我们决定销毁该servlet时候,不要把需要持久话的对象存放在内存中,因为在关闭的时候可能没有存放进数据库,造成数据的丢失.
        5. 具体的数据流程图
                                               
                                                servlet                                       
                                                   |
                                                   |生成实例
                                          |--------inti()
                                          |           |
                                          |           |成功
                                          |失败           |
                                          |         ready
                                          |           |
                                          |           |
                                          |------destroy