https://www.heckjj.com/index.php zh-cn https://www.heckjj.com/post// Heck <@hecks.tk> Thu, 24 Nov 2022 14:00:34 +0000 https://www.heckjj.com/post//
本文例子基于Github地址：https://github.com/pf4j/pf4j

<dependency>
  <groupId>org.pf4j</groupId>
  <artifactId>pf4j</artifactId>
  <version>3.6.0</version>
</dependency>
插件项目会涉及到3个工程：工程结构
plugin-api：定义可扩展接口
plugins：插件项目，可以包含多个插件，需要实现plugin-api中定义的接口
plugin-app：主程序，需要依赖plugin-api，加载并执行plugins
定义可扩展接口(plugin-api)
简单定义一个接口，需继承ExtensionPoint：

package plugin.api;

import org.pf4j.ExtensionPoint;

public interface Greeting extends ExtensionPoint {

    String getGreeting();
}
实现插件(plugins)
插件需要实现plugin-api定义的接口，并且使用@Extension标记：
package plugins;

import org.pf4j.Extension;
import plugin.api.Greeting;

@Extension
public class WelcomeGreeting implements Greeting {

    public String getGreeting() {
        return "Welcome";
    }
}

插件打包(plugins)
插件打包时，需要往MANIFEST.MF写入插件信息，此处使用maven插件(打包命令为package)：
<plugin>
  <groupId>org.apache.maven.plugins</groupId>
  <artifactId>maven-jar-plugin</artifactId>
  <version>2.3.1</version>
  <configuration>
    <archive>
      <manifestEntries>
        <Plugin-Id>welcome-plugin</Plugin-Id>
        <Plugin-Version>0.0.1</Plugin-Version>
      </manifestEntries>
    </archive>
  </configuration>
</plugin>


根据Github上介绍，MANIFEST.MF中Plugin-Id以及Plugin-Version是必须信息：

In above manifest I described a plugin with id welcome-plugin (mandatory attribute), with class org.pf4j.demo.welcome.WelcomePlugin (optional attribute), with version 0.0.1 (mandatory attribute) and with dependencies to plugins x, y, z (optional attribute).

此处定义插件ID为welcome-plugin，版本为0.0.1

加载执行插件(plugin-app)
package plugin.app;

import java.nio.file.Paths;
import java.util.List;

import org.pf4j.JarPluginManager;
import org.pf4j.PluginManager;

import plugin.api.Greeting;

public class Main {

    public static void main(String[] args) {
        // jar插件管理器
        PluginManager pluginManager = new JarPluginManager();

        // 加载指定路径插件
        pluginManager.loadPlugin(Paths.get("plugins-0.0.1-SNAPSHOT.jar"));

        // 启动指定插件(也可以加载所有插件)
        pluginManager.startPlugin("welcome-plugin");

        // 执行插件
        List<Greeting> greetings = pluginManager.getExtensions(Greeting.class);
        for (Greeting greeting : greetings) {
            System.out.println(">>> " + greeting.getGreeting());
        }

        // 停止并卸载指定插件
        pluginManager.stopPlugin("welcome-plugin");
        pluginManager.unloadPlugin("welcome-plugin");

    }
}



运行输出：

>>> Welcome
其他
插件周期
如果对插件生命周期(如加载，执行，停止等)有兴趣的话，可以实现插件类继承Plugin：

package plugins;

import org.pf4j.Plugin;
import org.pf4j.PluginWrapper;

public class WelcomePlugin extends Plugin {

    public WelcomePlugin(PluginWrapper wrapper) {
        super(wrapper);
    }

    @Override
    public void start() {
        System.out.println("WelcomePlugin.start()");
    }

    @Override
    public void stop() {
        System.out.println("WelcomePlugin.stop()");
    }

    @Override
    public void delete() {
        System.out.println("WelcomePlugin.delete()");
    }
}
同时往MANIFEST.MF写入插件信息：

<plugin>
  <groupId>org.apache.maven.plugins</groupId>
  <artifactId>maven-jar-plugin</artifactId>
  <version>2.3.1</version>
  <configuration>
    <archive>
      <manifestEntries>
        <Plugin-Id>welcome-plugin</Plugin-Id>
        <Plugin-Version>0.0.1</Plugin-Version>
        <!-- 新增 -->
        <Plugin-Class>plugins.WelcomePlugin</Plugin-Class>
      </manifestEntries>
    </archive>
  </configuration>
</plugin>
打包后运行输出：

WelcomePlugin.start()
>>> Welcome
WelcomePlugin.stop()
如果对运行流程感兴趣，或者调试，可以将日志级别设为debug日志
log4j.properties示例：

log4j.rootLogger = debug,stdout,log

log4j.appender.stdout = org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout = org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern = %d [%-5p] %l %r ms: %m%n

log4j.appender.log = org.apache.log4j.DailyRollingFileAppender
log4j.appender.log.DatePattern = _yyyy-MM-dd
log4j.appender.log.File = logs/debug.log
log4j.appender.log.Encoding = UTF-8
log4j.appender.log.layout = org.apache.log4j.PatternLayout
log4j.appender.log.layout.ConversionPattern = %d [%-5p] (%c.%t): %m%n ]]> https://www.heckjj.com/post//#blogcomment <user@domain.com> Thu, 01 Jan 1970 00:00:00 +0000 https://www.heckjj.com/post//#blogcomment