Question

我正在尝试能够进行全局异常捕获，以便在发生错误时添加额外信息。我有两个班，“履带”和“亚马逊”。我想要做的是能够调用“爬行”，在亚马逊中执行一个函数，并在爬行函数中使用异常处理。

以下是我的两个课程：

require 'mechanize'

class Crawler
  Mechanize.html_parser = Nokogiri::HTML

  def initialize
    @agent = Mechanize.new
  end

  def crawl
    puts "crawling"

    begin
      #execute code in Amazon class here?
    rescue Exception => e
      puts "Exception: #{e.message}"
      puts "On url: #{@current_url}"
      puts e.backtrace
    end
  end

  def get(url)
    @current_url = url
    @agent.get(url)
  end
end

class Amazon < Crawler
  #some code with errors
  def stuff
    page = get("http://www.amazon.com")
    puts page.parser.xpath("//asldkfjasdlkj").first['href']
  end
end

a = Amazon.new
a.crawl

有没有办法可以在“抓取”中调用“东西”，这样我就可以对整个东西函数使用异常处理了？有没有更好的方法来实现这一目标？

编辑：这是我最后做的事情

require 'mechanize'

class Crawler
  Mechanize.html_parser = Nokogiri::HTML

  def initialize
    @agent = Mechanize.new
  end

  def crawl
    yield
  rescue Exception => e
    puts "Exception: #{e.message}"
    puts "On url: #{@current_url}"
    puts e.backtrace
  end

  def get(url)
    @current_url = url
    @agent.get(url)
  end
end

c = Crawler.new

c.crawl do
  page = c.get("http://www.amazon.com")
  puts page.parser.xpath("//asldkfjasdlkj").first['href']
end

Answer 1

我设法通过“超级”和占位符功能获得所需的功能。还有更好的方法吗？

require 'mechanize'

class Crawler
  Mechanize.html_parser = Nokogiri::HTML

  def initialize
    @agent = Mechanize.new
  end

  def stuff
  end

  def crawl
    stuff
  rescue Exception => e
    puts "Exception: #{e.message}"
    puts "On url: #{@current_url}"
    puts e.backtrace
  end

  def get(url)
    @current_url = url
    @agent.get(url)
  end
end

class Amazon < Crawler
  #some code with errors
  def stuff
    super
    page = get("http://www.amazon.com")
    puts page.parser.xpath("//asldkfjasdlkj").first['href']
  end
end

a = Amazon.new
a.crawl

Answer 2

您可以抓取接受代码块：

def crawl
  begin
    yield
  rescue Exception => e
    # handle exceptoin
  end
end

def stuff
  crawl do
    # implementation of stuff
  end
end

我并不是因为没有身体的方法而疯狂。代码块在这里可能更有意义。根据您的要求，也可以消除子类化的需要。

Answer 3

如果你想要另一种方式，请看一下“策略”设计模式：

# test_mach.rb
require 'rubygems'
require 'mechanize'

# this is the context class,which calls the different strategy implementation
class Crawler
  def initialize(some_website_strategy)
    @strategy = some_website_strategy
  end

  def crawl
    begin
      @strategy.crawl
      #execute code in Amazon class here?
    rescue Exception => e
      puts "==== starts this exception comes from Parent Class"
      puts e.backtrace
      puts "==== ends  this exception comes from Parent Class"
    end
  end
end

# strategy class for Amazon
class Amazon
  def crawl
    puts "now crawling amazon"
    raise "oh ... some errors when crawling amazon"
  end
end

# strategy class for taobao.com 
class Taobao
  def crawl
    puts "now crawling taobao"
    raise "oh ... some errors when crawling taobao"
  end
end

然后运行此代码：

amazon = Crawler.new(Amazon.new)
amazon.crawl
taobao = Crawler.new(Taobao.new)
taobao.crawl

结果：

now crawling amazon
==== starts this exception comes from Parent Class
test_mach.rb:27:in `crawl'
test_mach.rb:13:in `crawl'
test_mach.rb:38
==== ends  this exception comes from Parent Class
now crawling taobao
==== starts this exception comes from Parent Class
test_mach.rb:34:in `crawl'
test_mach.rb:13:in `crawl'
test_mach.rb:40
==== ends  this exception comes from Parent Class

顺便说一句。对于你的实现，我基本上和你一样。除了

# my implementation
class Crawler
  def stuff
    raise "abstract method called"
  end
end

如果您想要另一种方式，请查看“别名”（＆lt;＆lt;＆lt; metaprogramming ruby＆gt;＆gt;，第155页）。但是我认为“围绕别名”是战略的复原案例。

（我的意思是，

在策略模式中，您首先要实现“上下文”类，然后您需要实现“策略”类。
但是在“围绕别名”法术中，你需要首先实现一个“策略”，然后你写一个新的类“围绕别名”“策略”......

错误...希望我没有让你困惑^ _ ^）

Ruby在继承的类中执行代码

3 个答案: