如何在java中覆盖服务提供者 [英] how to override a service provider in java
问题描述
这是一个更为常见的问题：
我正在使用xstream和woodstox，woodstox附带了一个服务提供程序，用于注册com.ctc.wstx.stax的woodstox jar中的javax.xml.stream.XMLOutputFactory。 WstxOutputFactory。
我想提供自己的javax.xml.stream.XMLOutputFactory，并且在类路径中仍然有woodstox jar。我知道我可以提供我自己的系统属性javax.xml.stream.XMLOutputFactory，但我正试图从我们的开发团队中解脱麻烦，并在我的jar中使用服务文件或者在我的战争中使用META -INF / services文件夹。查看javax.xml.stream.FactoryFinder的代码如何确保我的
META-INF / services / javax.xml.stream.XMLOutputFactory文件将是FactoryFinder使用的文件？
This is more a general question by example: I'm using xstream and woodstox, woodstox comes with a service provider for javax.xml.stream.XMLOutputFactory in woodstox jar registering com.ctc.wstx.stax.WstxOutputFactory. I want to provide my own javax.xml.stream.XMLOutputFactory and still have woodstox jar in the classpath. I know I can provide my own with the system property javax.xml.stream.XMLOutputFactory , but I'm trying to take off the hassle from our dev ops team and do it with a service file in my jar or maybe in my war's META-INF/services folder. looking the code of javax.xml.stream.FactoryFinder how can I make sure that my META-INF/services/javax.xml.stream.XMLOutputFactory file will be the one used by FactoryFinder?
我们将xstream与camel一起使用，无法找到将工厂注入XStreamDataFormat的方法
we use xstream with camel and could not find a way to inject the factory to XStreamDataFormat
推荐答案
首先：我强烈建议简化您的生活而不是使用它，而不是依赖于JDK SPI接口。它实际上没有增加注入 XMLInputFactory 和/或 XMLOutputFactory 的价值。对于注射，您可以使用Guice（或Spring）;或者只是手动传递它。由于这些工厂没有自己的依赖关系，这很容易。
First: instead of relying on JDK SPI interface, I strongly recommend simplifying your life and NOT using it. It really adds no value over injecting XMLInputFactory and/or XMLOutputFactory yourself. For injection you can use Guice (or Spring); or just pass it manually. Since these factories do not have dependencies of their own, this is easy.
但是如果选择（或必须）使用 XMLInputFactory.newInstance（ ），您可以为javax.xml.stream.XMLOutputFactory和javax.xml.stream.XMLInputFactory定义一个System属性。
But if choose to (or have to) use XMLInputFactory.newInstance(), you can define a System property for "javax.xml.stream.XMLOutputFactory" and "javax.xml.stream.XMLInputFactory".
那么为什么不使用JDK方法呢？多种原因：
So why not use JDK approach? Multiple reasons:
- 它增加了开销：如果你没有指定系统属性，它将必须扫描整个类路径，并使用大应用程序服务器大多数解析需要10x-100x
- 实现的优先级是未定义的：如果你在classpath中有多个，你会得到哪一个？谁知道......（注意：当你在类路径中添加新的jar时它甚至可能会改变）
- 你很可能通过传递依赖获得多个impl
不幸的是，Oracle似乎仍然坚持要为注册服务提供商添加这种已知错误的方法。为什么？可能是因为他们没有他们自己的DI lib /框架（Guice是谷歌，Spring by Springsource），他们往往很容易控制饥饿。
Unfortunately, Oracle still seems to insist on adding this known-faulty method for registering service providers. Why? Probably because they do not have a DI lib/framework of their own (Guice is by google, Spring by Springsource), and they tend to be pretty control hungry.
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