December 2019
Beginner to intermediate
330 pages
10h 7m
Chinese
Content preview from RxJava反应式编程
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152
｜
第
5
章
程数量有限，并且其中有一部分意外阻塞时，这可能会造成灾难性的影响。还记得基于
RxNetty
的服务器吗？它们最多只会使用几十个线程。另外一种灾难性的场景就是频繁调
用
URL.equals() 的时候，比如在 Set<URL> 中。URL 这种意料之外的行为是众所周知的，这
就好比一个事实：它的 equals() 实际会生成的结果取决于
Internet
的连接状况。
指出这一点只是为了说明编写反应式应用程序非常困难，而且陷阱重重。下一节将会介绍
另外一个更明显的阻塞源：数据库访问代码。
5.3
关系数据库访问
在前面的部分，我们已经得出结论：每个服务器最终都会成为不同服务的客户端。还有一
个非常有意思的现象，目前使用的计算机系统几乎全都是分布式的。由网线连接的两台计
算机需要进行通信时，在空间上实际已经是分布式的了。更极端一点，你可以将每台计算
机都想象成一个分布式系统，各个独立的
CPU
核心缓存并不总是一致的，它们必须通过
消息传递协议来实现同步。现在，让我们对比一下应用程序服务器和数据库服务器架构。
在
Java
领域，关系数据库访问长期存在的标准是
Java
数据库连接
（
Java Database
Connectivity
，
JDBC
）。从消费者的角度来说，
JDBC
提供了一组
API
与关系数据库进行通
信，这些数据库包括
PostgreSQL
、
Oracle Database
等。核心的抽象是
Connection
（
TCP/
IP
，线路连接）、Statement
（数据库查询）和
ResultSet
（查看数据库结果） ...
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