Dependency injection 依赖注入

This is more of a software engineering section than a Java section, but one of the best ways to write testable software is to use dependency injection (DI). Because Java strongly encourages OO design, to make testable software, you need to use DI.

这部分更像是谈论软件工程而不仅仅是Java，但是编写可测试软件的最佳方法之一就是使用依赖注入（DI）。因为Java非常推崇面向对象设计来保持软件的可测试性，你需要使用DI。

In Java, this is typically done with the Spring Framework. It has a either code-based wiring or XML configuration-based wiring. If you use the XML configuration, it's important that you don't overuse Spring because of its XML-based configuration format. There should be absolutely no logic or control structures in XML. It should only inject dependencies.

在Java里，实现DI的典型例子就是Spring框架。它既可以基于代码来装配，也可以基于XML文件来进行配置。如果使用XML配置的话，非常重要的一点就是不要滥用Spring，因为基于XML配置的格式问题。很显然不能够在XML里面放有任何逻辑或者控制结构，它仅仅用于注入依赖。

Good alternatives to using Spring is Google and Square's Dagger library or Google's Guice. They don't use Spring's XML configuration file format, and instead they put the injection logic in annotations and in code.

使用Spring的另一种选择是Google和Square的Dagger库或者是Google的Guice。他们不会使用Spring的XML配置文件格式，而是将注入逻辑放在代码的注解里面。