8.Quartz源码取经之插件模式

1.为什么用插件模式？

1.1 场景

想创建一个开放的应用，主应用只包含标准的功能，个性化的功能交给其他开发者实现

1.2 解决方法

• 主应用不知道子应用的存在：开放API，子应用独立运行。百度地图开放API、jar依赖、SDK、小程序¹都属于这种。
• 主应用知道子应用的存在，子应用运行依赖于主应用：插件模式

2.插件模式怎么实现–Quartz中的插件

2.1 定义插件接口

public interface SchedulerPlugin {
    void initialize(String name, Scheduler scheduler, ClassLoadHelper loadHelper)
        throws SchedulerException;
    void start();
    void shutdown();
}

• 说明：开发者开发插件时需实现上面的接口

2.2 初始化时注册插件

//StdSchudulerFactory的instantiate方法片段
//从配置文件中加载插件类，注册到QuartzSchedulerResources对象中
String[] pluginNames = cfg.getPropertyGroups(PROP_PLUGIN_PREFIX);
SchedulerPlugin[] plugins = new SchedulerPlugin[pluginNames.length];
        for (int i = 0; i < pluginNames.length; i++) {
            Properties pp = cfg.getPropertyGroup(PROP_PLUGIN_PREFIX + "."
                    + pluginNames[i], true);

            String plugInClass = pp.getProperty(PROP_PLUGIN_CLASS, null);

            if (plugInClass == null) {
                initException = new SchedulerException(
                        "SchedulerPlugin class not specified for plugin '"
                                + pluginNames[i] + "'");
                throw initException;
            }
            SchedulerPlugin plugin = null;
            try {
                plugin = (SchedulerPlugin)
                        loadHelper.loadClass(plugInClass).newInstance();
            } catch (Exception e) {
                initException = new SchedulerException(
                        "SchedulerPlugin class '" + plugInClass
                                + "' could not be instantiated.", e);
                throw initException;
            }
            try {
                setBeanProps(plugin, pp);
            } catch (Exception e) {
                initException = new SchedulerException(
                        "JobStore SchedulerPlugin '" + plugInClass
                                + "' props could not be configured.", e);
                throw initException;
            }

            plugins[i] = plugin;
        }
        // add plugins
            for (int i = 0; i < plugins.length; i++) {
                rsrcs.addSchedulerPlugin(plugins[i]);
            }

2.3 启动时调用插件的start方法

//QuartzScheduler中的方法，启动时会调用
private void startPlugins() {
        java.util.Iterator<SchedulerPlugin> itr = resources.getSchedulerPlugins().iterator();
        while (itr.hasNext()) {
            SchedulerPlugin plugin = itr.next();
            plugin.start();
        }
    }

3. Quartz插件示例

// quartz.properties文件配置
org.quartz.plugin.triggHistory.class: org.quartz.plugins.history.LoggingJobHistoryPlugin

public class LoggingTriggerHistoryPlugin implements SchedulerPlugin,
        TriggerListener {
     //此处省略了非插件相关代码
    /*
     * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     * 
     * Constructors.
     * 
     * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     */

    public LoggingTriggerHistoryPlugin() {
    }
    /*
     * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     * 
     * SchedulerPlugin Interface.
     * 
     * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     */

    public void initialize(String pname, Scheduler scheduler, ClassLoadHelper classLoadHelper)
        throws SchedulerException {
        this.name = pname;

        scheduler.getListenerManager().addTriggerListener(this,  EverythingMatcher.allTriggers());
    }

    public void start() {
        // do nothing...
    }
    public void shutdown() {
        // nothing to do...
    }
}

---

1. 2020新版微信小程序可以脱离微信客户端运行；以前版本以及其他小程序可能需要依赖于主应用 ↩︎