Java动态加载插件 [英] Java dynamically load plugin

问题描述

我想创建一个可以动态加载插件的应用程序，但我没有在互联网上找到任何文献。

I want to make an application that can dynamically load plug-ins but I've not found any literature on Internet.

困难的是：我不喜欢提前知道这个名字。

The difficult thing is: I don't know the name in advance.

例如我有一个插件界面：

public interface Plugin {
    public static Plugin newPlugin();
    public void executePlugin(String args[]);
}

以便每个在jar中实现插件的Class文件在列表中实例化：

So that every Class implementing Plugin in the jar file are instantiated in a list:

Method method = classToLoad.getMethod ("newPlugin");
mylist.add(method.invoke(null);

1. 第一个问题是，我在界面中没有静态方法。


2. 第二个问题是，我不知道如何查找实现界面

1. First problem is, I cannot have a static method in an interface.
2. Second problem is, I don't know how to find all classes that implement an interface

感谢您的帮助。

推荐答案

因此，您似乎希望在运行时动态发现实现特定接口的类（例如，插件）。您基本上有两种选择：

So it seems like you want to dynamically discover Classes that implement a specific interface (e.g., Plugin) at runtime. You have basically two choices for this:

1. 使用像osgi这样的组件框架


2. 使用Java的内部发现过程（ ServiceLoader ）

1. Use a component framework like osgi
2. Use Java's internal discovery process (ServiceLoader)

由于有许多关于osgi（也是小的）的好教程，我不会详细说明要使用Java的内部发现过程，您需要执行以下操作：

Since there are many good tutorials on osgi (also small ones), I will not detail that here. To use Java's internal discovery process, you need to do the following:

• 将您希望发现的所有新类捆绑到jar文件


• Cre在jar文件中使用里面的新文件： META-INF / services / package.Plugin 你必须在这里使用完整的包限定符


• 这个文件是一个简单的文本文件，包含在该jar文件中实现插件的每个类的完全限定名称


• 将该jar文件放入（可能已在运行的）应用程序的类路径中


• 发现服务：

• Bundle all "new" classes that you wish to discover into a jar file
• Create a new file inside the jar file: META-INF/services/package.Plugin You must use the full package qualifier here
• This file is a simple text file and contains the fully qualified name of each class implementing Plugin in that jar-file
• Place that jar file into the classpath of your (potentially already running) application
• Discover the services:

服务发现是这样完成的：

Service discovery is done like this:

ServiceLoader<Plugin> loader = ServiceLoader.load(Plugin.class)
for (Plugin p : loader) {
    // do something with the plugin
}

这里有更多细节： http://docs.oracle.com/javase/7/docs/api/java/util/ServiceLoader.html

对于接口中的静态方法：不可能。由于静态方法可以在没有类实例的情况下访问，并且接口只是定义方法而没有任何功能，因此它的语义也有些奇怪。因此，静态允许调用 Interface.doSomething（），而接口没有定义任何功能，这只会引起混淆。

As for static methods in interfaces: not possible. The semantics of that would also be somewhat weird as static methods are accessible without an instance of a class, and interfaces just define the methods, without any functionality. Thus, static would allow to call Interface.doSomething() whereas the interface does not define any functionality, this leads just to confusion.

编辑：

添加说明元文件中应包含的内容

added description what should be in the meta-file

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