Quartz Job Scheduling Framework［翻译］第八章. 使用 Quartz 插件 (第四部分)

2008-07-21 | 阅读(310)

四. 使用多个插件

你喜欢多少个，就可以在 quartz.properties 文件中注册多少个插件。然而，加载和初始化的顺序却不能保证，因为 Quartz 加载先把所有的属性到一个 Map 中，然后按照从 Map 中取出的顺序遍历插件。

为规避这一限制，你可以创建一个 Quartz 插件作为父插件，然后以给定的顺序加载其他多个插件。代码 8.6 显示了 ParentPlugin 长什么样子。

代码 8.6. ParentPlugin 能以特定的顺序加载子插件

package org.cavaness.quartzbook.chapter8;

import java.util.ArrayList;
import java.util.List;
import java.util.StringTokenizer;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.quartz.Scheduler;
import org.quartz.SchedulerConfigException;
import org.quartz.SchedulerException;
import org.quartz.spi.SchedulerPlugin;

public class ParentPlugin implements SchedulerPlugin {
    private static Log logger = LogFactory.getLog(ParentPlugin.class);

    // A list of child plug-ins
    private List childPlugins = new ArrayList();

    private String childPluginNames;

    private String pluginName;

    private Scheduler scheduler;

    /**
     * Default no-arg Constructor
     *
     */
    public ParentPlugin() {
    }

    /**
     * Pass the initialize call on to the child plug-ins.
     *
     * @throws SchedulerConfigException
     *             if there is an error initializing.
     */

    public void initialize(String name, final Scheduler scheduler)
              throws SchedulerException {

         this.pluginName = name;
         this.scheduler = scheduler;

         logger.info("Searching for child plugins to load");

         // The child plug-ins are comma-separated
         StringTokenizer tokenizer =
              new StringTokenizer(childPluginNames, ",");

         while (tokenizer.hasMoreElements()) {
              String pluginClassname = tokenizer.nextToken();

              try {
                   Class pluginClass =
                        Class.forName(pluginClassname);

                   Object obj = pluginClass.newInstance();

                   // Make sure the specified class is a plug-in
                   if (obj instanceof SchedulerPlugin) {
                        // Initialize the Plugin
                        SchedulerPlugin childPlugin =
                              (SchedulerPlugin) obj;

                             logger.info("Init child Plugin " +
                                  pluginClassname);

                        childPlugin.initialize(pluginClassname,
                             scheduler);

                        // Store the child plug-in in the list
                        childPlugins.add(childPlugin);
                   } else {
                        // Skip loading class
                        logger.error("Class is not a plugin " +
                             pluginClass);
                   }

              } catch (Exception ex) {
                   // On error, log and go to next child plug-in
                   logger.error("Error loading plugin " +
                        pluginClassname, ex);
              }
         }
    }
    public void start() {
         // Start each child plug-in
         int size = childPlugins.size();
         for (int i = 0; i < size; i++) {
              SchedulerPlugin childPlugin =
                   ((SchedulerPlugin) childPlugins.get(i));

              logger.info("Starting Child Plugin " + childPlugin);
              childPlugin.start();
         }
    }

    public void shutdown() {
         // Stop each child plug-in
         int size = childPlugins.size();
         for (int i = 0; i < size; i++) {
              SchedulerPlugin childPlugin =
                   ((SchedulerPlugin) childPlugins.get(i));

              logger.info("Stopping Plugin " + childPlugin);
              childPlugin.shutdown();
         }
    }

    public String getPluginName() {
         return pluginName;
    }

    public void setPluginName(String pluginName) {
         this.pluginName = pluginName;
    }

    public String getChildPluginNames() {
         return childPluginNames;
    }

    public void setChildPluginNames(String childPluginNames) {
         this.childPluginNames = childPluginNames;
    }
}

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package org.cavaness.quartzbook.chapter8;

import java.util.ArrayList;

import java.util.List;

import java.util.StringTokenizer;

import org.apache.commons.logging.Log;

import org.apache.commons.logging.LogFactory;

import org.quartz.Scheduler;

import org.quartz.SchedulerConfigException;

import org.quartz.SchedulerException;

import org.quartz.spi.SchedulerPlugin;

public class ParentPlugin implements SchedulerPlugin {

private static Log logger = LogFactory.getLog(ParentPlugin.class);

// A list of child plug-ins

private List childPlugins = new ArrayList();

private String childPluginNames;

private String pluginName;

private Scheduler scheduler;

/**

* Default no-arg Constructor

public ParentPlugin() {

}

/**

* Pass the initialize call on to the child plug-ins.

* @throws SchedulerConfigException

* if there is an error initializing.

public void initialize(String name, final Scheduler scheduler)

throws SchedulerException {

this.pluginName = name;

this.scheduler = scheduler;

logger.info("Searching for child plugins to load");

// The child plug-ins are comma-separated

StringTokenizer tokenizer =

new StringTokenizer(childPluginNames, ",");

while (tokenizer.hasMoreElements()) {

String pluginClassname = tokenizer.nextToken();

try {

Class pluginClass =

Class.forName(pluginClassname);

Object obj = pluginClass.newInstance();

// Make sure the specified class is a plug-in

if (obj instanceof SchedulerPlugin) {

// Initialize the Plugin

SchedulerPlugin childPlugin =

(SchedulerPlugin) obj;

logger.info("Init child Plugin " +

pluginClassname);

childPlugin.initialize(pluginClassname,

scheduler);

// Store the child plug-in in the list

childPlugins.add(childPlugin);

} else {

// Skip loading class

logger.error("Class is not a plugin " +

pluginClass);

}

} catch (Exception ex) {

// On error, log and go to next child plug-in

logger.error("Error loading plugin " +

pluginClassname, ex);

}

public void start() {

// Start each child plug-in

int size = childPlugins.size();

for (int i = 0; i < size; i++) {

SchedulerPlugin childPlugin =

((SchedulerPlugin) childPlugins.get(i));

logger.info("Starting Child Plugin " + childPlugin);

childPlugin.start();

}

public void shutdown() {

// Stop each child plug-in

int size = childPlugins.size();

for (int i = 0; i < size; i++) {

SchedulerPlugin childPlugin =

((SchedulerPlugin) childPlugins.get(i));

logger.info("Stopping Plugin " + childPlugin);

childPlugin.shutdown();

}

public String getPluginName() {

return pluginName;

}

public void setPluginName(String pluginName) {

this.pluginName = pluginName;

}

public String getChildPluginNames() {

return childPluginNames;

}

public void setChildPluginNames(String childPluginNames) {

this.childPluginNames = childPluginNames;

}

代码 8.6 中的插件基什么也不做，也就只能算作一个插件，但是它扮演着子插件的加载器。一个子插件是个有效的 Quartz 插件，它可以是你所编写的或者是包含在框架中的。

·配置文件 quartz.properties 中的 ParentPlugin

要配置 quartz.properties 文件中的 ParentPlugin，仅要加入作为其他插件的父类。那就是，添加如下的行：

org.quartz.plugin.parentPlugin.class = org.cavaness.quartzbook.chapter8.ParentPlugin

接着，添加子插件，并按你想要的加载顺序排列，就是指定一个逗号分隔的插件列表：

org.quartz.plugin.parentPlugin.childPluginNames=org.quartz.plugins.history
　　.LoggingJobHistoryPlugin,org.quartz.plugins.history.LoggingTriggerHistoryPlugin

[译者 Unmi 注：注意，上面是写在一行里的，因页面排版本的原因写成两行了]

如代码 8.6 所示，ParentPlugin 拆开逗号分隔的字符串并以它们在列表中的顺序来加载插件。这看起来好像相当复杂，但却能很好的完成工作。将来的 Quartz 框架版本也许支持插件的按序加载机制，但是现在，ParentPlugin 工作的很好。

本文链接 https://yanbin.blog/quartz-job-scheduling-framework-8-4/, 来自隔叶黄莺 Yanbin Blog

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