Hadoop源码分析(2)——Configuration类

public static void main(String[] args) throws Exception {
     int res = ToolRunner.run(new Configuration(), new CalculateSumJob(),args);
     System.exit(res);
}

  public static synchronized void addDefaultResource(String name) {
    if(!defaultResources.contains(name)) {
      defaultResources.add(name);
      for(Configuration conf : REGISTRY.keySet()) {
        if(conf.loadDefaults) {
          conf.reloadConfiguration();
        }
      }
    }
  }

private void loadResources(Properties properties,
                             ArrayList resources,
                             boolean quiet) {
    if(loadDefaults) {
      for (String resource : defaultResources) {
        loadResource(properties, resource, quiet);
      }
    
      //support the hadoop-site.xml as a deprecated case
      if(getResource("hadoop-site.xml")!=null) {
        loadResource(properties, "hadoop-site.xml", quiet);
      }
    }
    else{
         for (Object resource : resources) {
            loadResource(properties, resource, quiet);
         }
    }
  }

 private void loadResource(Properties properties, Object name, boolean quiet) {
    try {
      DocumentBuilderFactory docBuilderFactory 
        = DocumentBuilderFactory.newInstance();
      //ignore all comments inside the xml file
      docBuilderFactory.setIgnoringComments(true);

      //allow includes in the xml file
      docBuilderFactory.setNamespaceAware(true);
      try {
          docBuilderFactory.setXIncludeAware(true);
      } catch (UnsupportedOperationException e) {
        LOG.error("Failed to set setXIncludeAware(true) for parser "
                + docBuilderFactory
                + ":" + e,
                e);
      }
      DocumentBuilder builder = docBuilderFactory.newDocumentBuilder();
      Document doc = null;
      Element root = null;

      if (name instanceof URL) {                  // an URL resource
        URL url = (URL)name;
        if (url != null) {
          if (!quiet) {
            LOG.info("parsing " + url);
          }
          doc = builder.parse(url.toString());
        }
      } else if (name instanceof String) {        // a CLASSPATH resource
        URL url = getResource((String)name);
        if (url != null) {
          if (!quiet) {
            LOG.info("parsing " + url);
          }
          doc = builder.parse(url.toString());
        }
      } else if (name instanceof Path) {          // a file resource
        // Can‘t use FileSystem API or we get an infinite loop
        // since FileSystem uses Configuration API.  Use java.io.File instead.
        File file = new File(((Path)name).toUri().getPath())
          .getAbsoluteFile();
        if (file.exists()) {
          if (!quiet) {
            LOG.info("parsing " + file);
          }
          InputStream in = new BufferedInputStream(new FileInputStream(file));
          try {
            doc = builder.parse(in);
          } finally {
            in.close();
          }
        }
      } else if (name instanceof InputStream) {
        try {
          doc = builder.parse((InputStream)name);
        } finally {
          ((InputStream)name).close();
        }
      } else if (name instanceof Element) {
        root = (Element)name;
      }

      if (doc == null && root == null) {
        if (quiet)
          return;
        throw new RuntimeException(name + " not found");
      }

      if (root == null) {
        root = doc.getDocumentElement();
      }
      if (!"configuration".equals(root.getTagName()))
        LOG.fatal("bad conf file: top-level element not <configuration>");
      NodeList props = root.getChildNodes();
      for (int i = 0; i < props.getLength(); i++) {
        Node propNode = props.item(i);
        if (!(propNode instanceof Element))
          continue;
        Element prop = (Element)propNode;
        if ("configuration".equals(prop.getTagName())) {
          loadResource(properties, prop, quiet);
          continue;
        }
        if (!"property".equals(prop.getTagName()))
          LOG.warn("bad conf file: element not <property>");
        NodeList fields = prop.getChildNodes();
        String attr = null;
        String value = null;
        boolean finalParameter = false;
        for (int j = 0; j < fields.getLength(); j++) {
          Node fieldNode = fields.item(j);
          if (!(fieldNode instanceof Element))
            continue;
          Element field = (Element)fieldNode;
          if ("name".equals(field.getTagName()) && field.hasChildNodes())
            attr = ((Text)field.getFirstChild()).getData().trim();
          if ("value".equals(field.getTagName()) && field.hasChildNodes())
            value = ((Text)field.getFirstChild()).getData();
          if ("final".equals(field.getTagName()) && field.hasChildNodes())
            finalParameter = "true".equals(((Text)field.getFirstChild()).getData());
        }
        
        // Ignore this parameter if it has already been marked as ‘final‘
        if (attr != null) {
          if (value != null) {
            if (!finalParameters.contains(attr)) {
              properties.setProperty(attr, value);
              if (storeResource) {
                updatingResource.put(attr, name.toString());
              }
            } else if (!value.equals(properties.getProperty(attr))) {
              LOG.warn(name+":a attempt to override final parameter: "+attr
                     +";  Ignoring.");
            }
          }
          if (finalParameter) {
            finalParameters.add(attr);
          }
        }
      }
        
    } catch (IOException e) {
      LOG.fatal("error parsing conf file: " + e);
      throw new RuntimeException(e);
    } catch (DOMException e) {
      LOG.fatal("error parsing conf file: " + e);
      throw new RuntimeException(e);
    } catch (SAXException e) {
      LOG.fatal("error parsing conf file: " + e);
      throw new RuntimeException(e);
    } catch (ParserConfigurationException e) {
      LOG.fatal("error parsing conf file: " + e);
      throw new RuntimeException(e);
    }
  }

private synchronized Properties getProps() {
    if (properties == null) {
      properties = new Properties();
      loadResources(properties, resources, quietmode);
      if (overlay!= null) {
        properties.putAll(overlay);
        if (storeResource) {
          for (Map.Entry<Object,Object> item: overlay.entrySet()) {
            updatingResource.put((String) item.getKey(), "Unknown");
          }
        }
      }
    }
    return properties;
  }