Nutch 1.0 源代码分析［2］ Plugin(1)

    借着URLNormalizers看一下Nutch的插件机制，在Injector类中的configure类中有一句是：

urlNormalizers = newURLNormalizers(job,

       URLNormalizers.SCOPE_INJECT);

    它调用的是：

publicURLNormalizers(Configuration conf, String scope) {

    this.conf =conf;

    this.extensionPoint =PluginRepository

.get(conf).getExtensionPoint(URLNormalizer.X_POINT_ID);

    ObjectCache objectCache = ObjectCache.get(conf);

    normalizers =(URLNormalizer[]) objectCache

           .getObject(URLNormalizer.X_POINT_ID + "_" +scope);

    if (normalizers == null) {

       normalizers =getURLNormalizers(scope);

    }

    if (normalizers == EMPTY_NORMALIZERS) {

       normalizers =(URLNormalizer[]) objectCache

              .getObject(URLNormalizer.X_POINT_ID + "_"

+ SCOPE_DEFAULT);

       if (normalizers == null) {

           normalizers =getURLNormalizers(SCOPE_DEFAULT);

       }

    }

    loopCount =conf.getInt("urlnormalizer.loop.count", 1);

}

    这里的getExtensionPoint是得到相应的扩展点，这里URLNormailizer.X_POINT_ID是org.apache.nutch.net.URLNormalizer，关于扩展点可以看一下IBM的技术文章《Nutch 插件系统浅析》，接下来先到缓存中去找，如果没有找到就调用getURLNormalizers()，如果normalizers==EMPTY_NORMALIZERS说明它应该在缓存里有，如果缓存里存的是null，就用默认的normalizer，而loopCount是在规范化时指定要循环多少次的一个值。getURLNormalizers代码如下：

URLNormalizer[]getURLNormalizers(String scope) {

    List<Extension> extensions =getExtensions(scope);

    List<URLNormalizer> normalizers = new

       Vector<URLNormalizer>(extensions.size());

    Iterator<Extension> it =extensions.iterator();

    while(it.hasNext()) {

       Extension ext = it.next();

       URLNormalizer normalizer = null;

       try {

           normalizer = (URLNormalizer)objectCache

.getObject(ext.getId());

           if(normalizer == null) {

              // go aheadand instantiate it and then cache it

              normalizer = (URLNormalizer)ext.getExtensionInstance();

              objectCache.setObject(ext.getId(),normalizer);

           }

           normalizers.add(normalizer);

       } catch(PluginRuntimeException e) {

       }

    }

    returnnormalizers.toArray(newURLNormalizer[normalizers.size()]);

}

    得到相应scope的Extensions，先不去管它是如何得到的，这里将得到的Extension实例化，保存到normalizers中。下面则是getExtensions的代码：

privateList<Extension> getExtensions(String scope) {

https://c.tieba.baidu.com/p/3476776824
https://c.tieba.baidu.com/p/3476808306
https://c.tieba.baidu.com/p/3476798710
https://c.tieba.baidu.com/p/3474281354
https://c.tieba.baidu.com/p/3474300101
https://c.tieba.baidu.com/p/3474294075
https://c.tieba.baidu.com/p/3474123295
https://c.tieba.baidu.com/p/3474314242
https://c.tieba.baidu.com/p/3474310411
https://c.tieba.baidu.com/p/3474304550
https://c.tieba.baidu.com/p/3475433945
https://c.tieba.baidu.com/p/3475430015
https://c.tieba.baidu.com/p/3475433348
https://c.tieba.baidu.com/p/3475431434
https://c.tieba.baidu.com/p/3474176863
https://c.tieba.baidu.com/p/3474159835
https://c.tieba.baidu.com/p/3474163941
https://c.tieba.baidu.com/p/3474156121
https://c.tieba.baidu.com/p/3474147660
https://c.tieba.baidu.com/p/3474151899
https://c.tieba.baidu.com/p/3474142287
https://c.tieba.baidu.com/p/3474136965
https://c.tieba.baidu.com/p/3474133165
https://c.tieba.baidu.com/p/3474128675
https://c.tieba.baidu.com/p/3474103896
https://c.tieba.baidu.com/p/3474099488
https://c.tieba.baidu.com/p/3474094120
https://c.tieba.baidu.com/p/3475431976
https://c.tieba.baidu.com/p/3474267991
https://c.tieba.baidu.com/p/3474259583
https://c.tieba.baidu.com/p/3474254990
https://c.tieba.baidu.com/p/3474228986
https://c.tieba.baidu.com/p/3474221626
https://c.tieba.baidu.com/p/3474215742
https://c.tieba.baidu.com/p/3474212122
https://c.tieba.baidu.com/p/3474188883
https://c.tieba.baidu.com/p/3474207722
https://c.tieba.baidu.com/p/3474184143
https://c.tieba.baidu.com/p/3474180522
https://c.tieba.baidu.com/p/3474171022
https://c.tieba.baidu.com/p/3474086627