Java 应用程序引擎服务的适当范围

创建servlet时，应用引擎服务的适当范围是什么：静态、实例还是本地？和每种方法的含义是什么？似乎您应该在尽可能广泛的范围内使用它们，以避免重新创建（或重新检索）它们的开销，但我想知道这是否会导致数据的不当重用，尤其是在

true

的情况下

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下面提供了每个范围的示例。将在下面的示例中使用，但我的问题适用于任何和所有服务（尽管我不确定答案是否取决于所使用的服务）。我常用、、和

静态范围：

public class MyServlet extends HttpServlet {
    private static MemcacheService memcacheService = MemcacheServiceFactory.getMemcacheService();

    @Override
    public void doGet(HttpServletRequest req, HttpServletResponse resp) {
        memcacheService.get("x");
    }
}

public class MyServlet extends HttpServlet {
    private MemcacheService memcacheService = MemcacheServiceFactory.getMemcacheService();

    @Override
    public void doGet(HttpServletRequest req, HttpServletResponse resp) {
        memcacheService.get("x");
    }
}

public class MyServlet extends HttpServlet {
    @Override
    public void doGet(HttpServletRequest req, HttpServletResponse resp) {
        MemcacheService memcacheService = MemcacheServiceFactory.getMemcacheService();
        memcacheService.get("x");
    }
}

实例成员：

public class MyServlet extends HttpServlet {
    private static MemcacheService memcacheService = MemcacheServiceFactory.getMemcacheService();

    @Override
    public void doGet(HttpServletRequest req, HttpServletResponse resp) {
        memcacheService.get("x");
    }
}

public class MyServlet extends HttpServlet {
    private MemcacheService memcacheService = MemcacheServiceFactory.getMemcacheService();

    @Override
    public void doGet(HttpServletRequest req, HttpServletResponse resp) {
        memcacheService.get("x");
    }
}

public class MyServlet extends HttpServlet {
    @Override
    public void doGet(HttpServletRequest req, HttpServletResponse resp) {
        MemcacheService memcacheService = MemcacheServiceFactory.getMemcacheService();
        memcacheService.get("x");
    }
}

本地范围：

public class MyServlet extends HttpServlet {
    private static MemcacheService memcacheService = MemcacheServiceFactory.getMemcacheService();

    @Override
    public void doGet(HttpServletRequest req, HttpServletResponse resp) {
        memcacheService.get("x");
    }
}

public class MyServlet extends HttpServlet {
    private MemcacheService memcacheService = MemcacheServiceFactory.getMemcacheService();

    @Override
    public void doGet(HttpServletRequest req, HttpServletResponse resp) {
        memcacheService.get("x");
    }
}

public class MyServlet extends HttpServlet {
    @Override
    public void doGet(HttpServletRequest req, HttpServletResponse resp) {
        MemcacheService memcacheService = MemcacheServiceFactory.getMemcacheService();
        memcacheService.get("x");
    }
}

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GAE是一个分布式系统，它的所有服务都运行在不同的服务器上。因此，当您调用服务时，它会在内部序列化请求（使用协议缓冲区的afaik）将其发送到运行该服务的服务器，检索结果并反序列化它

所以所有的

*服务

类基本上都是围绕序列化/反序列化代码的非常薄的包装。例如，见

---

关于范围：不需要优化

*服务

类，因为它们是非常薄的包装，创建它们所需的时间与整个服务往返相比应该可以忽略不计。

完整、简洁的答案，有源代码支持。谢谢。是的，但是让它们成为能够在单元测试中模拟它们的字段仍然是有意义的。