java - 为什么 pluginManager.getExtensions 的结果为空？

Question

尝试使用 PF4J 时，我创建了必要的部分，如

扩展 ExtensionPoint 的接口
一个插件
带有清单的罐子
插件加载和激活

为什么 clickHandlers 列表是空的？

我已经使用 JUnit 测试对此进行了测试，我可以在其中调试似乎工作正常的其他部分。请参阅下面的调试日志。

我还查看了https://github.com/pf4j/pf4j/issues/21并激活了 Eclipse 注释处理，但没有任何积极影响。

1.扩展扩展点的接口

public interface ClickHandler extends ExtensionPoint {
...

}

2.一个插件

public class MBClickHandlerPlugin extends Plugin {

  /**
   * construct me
   * @param wrapper
   */
  public MBClickHandlerPlugin(PluginWrapper wrapper) {
    super(wrapper);
  }

  @Extension
  public static class  MBClickHandler implements ClickHandler {


  }
}

3. 带有清单的罐子

unzip -q -c target/com.bitplan.mb-0.0.1.jar META-INF/MANIFEST.MF
Manifest-Version: 1.0
Plugin-Dependencies: 
Plugin-Id: com.bitplan.mb
Built-By: wf
Plugin-Provider: BITPlan GmbH
Plugin-Version: 0.0.1
Plugin-Class: com.bitplan.mb.MBClickHandlerPlugin
Created-By: Apache Maven 3.5.2
Build-Jdk: 1.8.0_152

4.插件加载和激活

  /**
   * activate the plugins requested on the command line
   */
  public void activatePlugins() {
    pluginManager = new DefaultPluginManager();

    for (String plugin : plugins) {
      Path pluginPath = Paths.get(plugin);
      pluginManager.loadPlugin(pluginPath);
    }
    pluginManager.startPlugins();

    List<ClickHandler> clickHandlers = pluginManager
        .getExtensions(ClickHandler.class);
    for (ClickHandler clickHandler : clickHandlers) {
      installClickHandler(clickHandler);
    }
  }

调试日志

22 [main] DEBUG org.pf4j.CompoundPluginDescriptorFinder  - Try to continue with the next finder
22 [main] DEBUG org.pf4j.CompoundPluginDescriptorFinder  - 'org.pf4j.ManifestPluginDescriptorFinder@73d4cc9e' is applicable for plugin '/Users/wf/Documents/workspace/com.bitplan.mb/target/com.bitplan.mb-0.0.1.jar'
24 [main] DEBUG org.pf4j.AbstractPluginManager  - Found descriptor PluginDescriptor [pluginId=com.bitplan.mb, pluginClass=com.bitplan.mb.MBClickHandlerPlugin, version=0.0.1, provider=BITPlan GmbH, dependencies=[], description=, requires=*, license=null]
24 [main] DEBUG org.pf4j.AbstractPluginManager  - Class 'com.bitplan.mb.MBClickHandlerPlugin' for plugin '/Users/wf/Documents/workspace/com.bitplan.mb/target/com.bitplan.mb-0.0.1.jar'
24 [main] DEBUG org.pf4j.AbstractPluginManager  - Loading plugin '/Users/wf/Documents/workspace/com.bitplan.mb/target/com.bitplan.mb-0.0.1.jar'
24 [main] DEBUG org.pf4j.CompoundPluginLoader  - 'org.pf4j.DefaultPluginLoader@6366ebe0' is not applicable for plugin '/Users/wf/Documents/workspace/com.bitplan.mb/target/com.bitplan.mb-0.0.1.jar'
24 [main] DEBUG org.pf4j.CompoundPluginLoader  - 'org.pf4j.JarPluginLoader@44f75083' is applicable for plugin '/Users/wf/Documents/workspace/com.bitplan.mb/target/com.bitplan.mb-0.0.1.jar'
25 [main] DEBUG org.pf4j.PluginClassLoader  - Add 'file:/Users/wf/Documents/workspace/com.bitplan.mb/target/com.bitplan.mb-0.0.1.jar'
25 [main] DEBUG org.pf4j.AbstractPluginManager  - Loaded plugin '/Users/wf/Documents/workspace/com.bitplan.mb/target/com.bitplan.mb-0.0.1.jar' with class loader 'org.pf4j.PluginClassLoader@43d7741f'
25 [main] DEBUG org.pf4j.AbstractPluginManager  - Creating wrapper for plugin '/Users/wf/Documents/workspace/com.bitplan.mb/target/com.bitplan.mb-0.0.1.jar'
25 [main] DEBUG org.pf4j.AbstractPluginManager  - Created wrapper 'PluginWrapper [descriptor=PluginDescriptor [pluginId=com.bitplan.mb, pluginClass=com.bitplan.mb.MBClickHandlerPlugin, version=0.0.1, provider=BITPlan GmbH, dependencies=[], description=, requires=*, license=null], pluginPath=/Users/wf/Documents/workspace/com.bitplan.mb/target/com.bitplan.mb-0.0.1.jar]' for plugin '/Users/wf/Documents/workspace/com.bitplan.mb/target/com.bitplan.mb-0.0.1.jar'
26 [main] DEBUG org.pf4j.DependencyResolver  - Graph: 
   com.bitplan.mb -> []
26 [main] DEBUG org.pf4j.DependencyResolver  - Plugins order: [com.bitplan.mb]
27 [main] INFO org.pf4j.AbstractPluginManager  - Plugin 'com.bitplan.mb@0.0.1' resolved
27 [main] INFO org.pf4j.AbstractPluginManager  - Start plugin 'com.bitplan.mb@0.0.1'
27 [main] DEBUG org.pf4j.DefaultPluginFactory  - Create instance for plugin 'com.bitplan.mb.MBClickHandlerPlugin'
28 [main] DEBUG org.pf4j.AbstractExtensionFinder  - Finding extensions of extension point 'com.bitplan.uml2mxgraph.ClickHandler'
28 [main] DEBUG org.pf4j.LegacyExtensionFinder  - Reading extensions storages from classpath
28 [main] DEBUG org.pf4j.AbstractExtensionFinder  - No extensions found
28 [main] DEBUG org.pf4j.LegacyExtensionFinder  - Reading extensions storages from plugins
28 [main] DEBUG org.pf4j.LegacyExtensionFinder  - Reading extensions storage from plugin 'com.bitplan.mb'
28 [main] DEBUG org.pf4j.LegacyExtensionFinder  - Cannot find 'META-INF/extensions.idx'
28 [main] DEBUG org.pf4j.AbstractExtensionFinder  - No extensions found
28 [main] DEBUG org.pf4j.AbstractExtensionFinder  - Finding extensions of extension point 'com.bitplan.uml2mxgraph.ClickHandler' for plugin 'null'
28 [main] DEBUG org.pf4j.AbstractExtensionFinder  - Finding extensions of extension point 'com.bitplan.uml2mxgraph.ClickHandler' for plugin 'com.bitplan.mb'
29 [main] DEBUG org.pf4j.AbstractExtensionFinder  - Found 0 extensions for extension point 'com.bitplan.uml2mxgraph.ClickHandler

'

score 1 · Accepted Answer

解决方法 #1

使用定制的 PluginManager

pluginManager = new JarPluginManager(this.getClass().getClassLoader());

从将使用插件的类中确保使用相同的类加载器

JarPluginManager 源代码：

import java.nio.file.Path;

import org.pf4j.DefaultPluginManager;
import org.pf4j.JarPluginLoader;
import org.pf4j.ManifestPluginDescriptorFinder;
import org.pf4j.PluginClassLoader;
import org.pf4j.PluginDescriptor;
import org.pf4j.PluginDescriptorFinder;
import org.pf4j.PluginLoader;
import org.pf4j.PluginManager;

/**
 * see https://github.com/pf4j/pf4j/issues/249 see
 * https://pf4j.org/doc/class-loading.html
 * 
 * @author wf
 *
 */
public class JarPluginManager extends DefaultPluginManager {
  public static class ParentClassLoaderJarPluginLoader extends JarPluginLoader {
    static ClassLoader parentClassLoader;

    /**
     * 
     * @param pluginManager
     */
    public ParentClassLoaderJarPluginLoader(PluginManager pluginManager) {
      super(pluginManager);
    }

    static PluginClassLoader pluginClassLoader;

    @Override
    public ClassLoader loadPlugin(Path pluginPath,
        PluginDescriptor pluginDescriptor) {
      if (pluginClassLoader == null) {
        boolean parentFirst=true;
        pluginClassLoader = new PluginClassLoader(pluginManager,
            pluginDescriptor, parentClassLoader,parentFirst);
      }
      pluginClassLoader.addFile(pluginPath.toFile());

      return pluginClassLoader;
    }
  }

  /**
   * construct me with the given classloader
   * @param classLoader
   */
  public JarPluginManager(ClassLoader classLoader) {
    ParentClassLoaderJarPluginLoader.parentClassLoader=classLoader;
    //System.setProperty("pf4j.mode", RuntimeMode.DEPLOYMENT.toString());
    //System.setProperty("pf4j.mode", RuntimeMode.DEVELOPMENT.toString());
  }

  @Override
  protected PluginLoader createPluginLoader() {
    // load only jar plugins
    return new ParentClassLoaderJarPluginLoader(this);
  }

  @Override
  protected PluginDescriptorFinder createPluginDescriptorFinder() {
    // read plugin descriptor from jar's manifest
    return new ManifestPluginDescriptorFinder();
  }

}

解决方法 #2 如果未创建 extensions.idx 文件，则说明您的注释处理有问题。您可能想解决问题的根源，但也可以尝试解决它：

https://groups.google.com/forum/#!topic/pf4j/nn20axJHpfI 指出我手动创建 META-INF/extensions.idx 文件并确保静态内部类没有 args 构造函数。有了这个改变，事情就开始了。
注意在 extensions.idx 文件中正确设置类名 - 否则您将在处理程序列表中得到一个空条目
注意有一个空参数构造函数，否则你会得到一个异常

@Extension
public static class  MBClickHandler implements ClickHandler {
  /**
   * constructor with no argument
   */
  public MBClickHandler() {

  }

src/main/resources/META-INF/extensions.idx

com.bitplan.mb.MBClickHandlerPlugin$MBClickHandler

要检查的代码

extension.idx 条目的正确名称

MBClickHandler ch=new MBClickHandler();
File extFile=new File("src/main/resources/META-INF/extensions.idx");
String extidx=FileUtils.readFileToString(extFile,"UTF-8");
assertEquals(extidx,ch.getClass().getName());

检查扩展

List<PluginWrapper> startedPlugins = pluginManager.getStartedPlugins();

    for (PluginWrapper plugin : startedPlugins) {
       String pluginId = plugin.getDescriptor().getPluginId();
       System.out.println(String.format("Extensions added by plugin '%s':", pluginId));
       Set<String> extensionClassNames = pluginManager.getExtensionClassNames(pluginId);
       for (String extension : extensionClassNames) {
           System.out.println("   " + extension);
       }
    }

java - 为什么 pluginManager.getExtensions 的结果为空？

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