Clojure XML流关闭异常
我在解析带有Clojure XML流关闭异常,xml,clojure,xml-parsing,Xml,Clojure,Xml Parsing,我在解析带有clojure.data.XML的XML文件时遇到异常,因为在解析完成之前流已关闭 我不明白的是,为什么doall在with open关闭XML数据之前不强制对其求值(如所建议的): 这会引发异常: (file->xml "example.xml") ;-> XMLStreamException ParseError at [row,col]:[80,1926] Message: Stream closed com.sun.org.apache.xerces.intern
clojure.data.XML
的XML文件时遇到异常,因为在解析完成之前流已关闭
我不明白的是,为什么doall
在with open
关闭XML数据之前不强制对其求值(如所建议的):
这会引发异常:
(file->xml "example.xml")
;-> XMLStreamException ParseError at [row,col]:[80,1926]
Message: Stream closed com.sun.org.apache.xerces.internal.impl.XMLStreamReaderImpl.next
如果我用open包装器删除,它将按预期返回XML数据(因此,尽管不能保证读卡器已关闭,但该文件是合法的)
我发现(源xml/parse)
会产生惰性结果:
(defn parse
"Parses the source, which can be an
InputStream or Reader, and returns a lazy tree of Element records.
Accepts key pairs with XMLInputFactory options, see http://docs.oracle.com/javase/6/docs/api/javax/xml/stream/XMLInputFactory.html
and xml-input-factory-props for more information.
Defaults coalescing true."
[source & opts]
(event-tree (event-seq source opts)))
也许这是相关的,但我的函数与上的“往返”示例非常相似
我在这里遗漏了什么?看到这种行为我很惊讶。似乎clojure.data.xml.Element
(返回类型)实现了一种“惰性映射”,它不受doall
的影响
以下是将惰性值转换为法线贴图的解决方案:
(ns tst.clj.core
(:use clj.core clojure.test tupelo.test)
(:require
[tupelo.core :as t]
[clojure.string :as str]
[clojure.pprint :refer [pprint]]
[clojure.java.io :as io]
[clojure.data.xml :as xml]
[clojure.walk :refer [postwalk]]
))
(t/refer-tupelo)
(defn unlazy
[coll]
(let [unlazy-item (fn [item]
(cond
(sequential? item) (vec item)
(map? item) (into {} item)
:else item))
result (postwalk unlazy-item coll) ]
result ))
(defn file->xml [path]
(with-open [rdr (-> path io/resource io/reader) ]
(let [lazy-vals (xml/parse rdr)
eager-vals (unlazy lazy-vals) ]
eager-vals)))
(pprint (file->xml "books.xml"))
{:tag :catalog,
:attrs {},
:content
[{:tag :book,
:attrs {:id "bk101"},
:content
[{:tag :author, :attrs {}, :content ["Gambardella, Matthew"]}
{:tag :title, :attrs {}, :content ["XML Developer's Guide"]}
{:tag :genre, :attrs {}, :content ["Computer"]}
{:tag :price, :attrs {}, :content ["44.95"]}
{:tag :publish_date, :attrs {}, :content ["2000-10-01"]}
{:tag :description,
:attrs {},
:content
["An in-depth look at creating applications\n with XML."]}]}
{:tag :book,
:attrs {:id "bk102"},
:content
[{:tag :author, :attrs {}, :content ["Ralls, Kim"]}
{:tag :title, :attrs {}, :content ["Midnight Rain"]}
{:tag :genre, :attrs {}, :content ["Fantasy"]}
{:tag :price, :attrs {}, :content ["5.95"]}
{:tag :publish_date, :attrs {}, :content ["2000-12-16"]}
{:tag :description,
:attrs {},
:content
["A former architect battles corporate zombies,\n an evil sorceress, and her own childhood to become queen\n of the world."]}]}
{:tag :book,
:attrs {:id "bk103"},
:content .....
由于clojure.data.xml.Element
实现了clojure.lang.IPersistentMap
,因此使用(map?项)
返回true
这是你的电话号码
请注意:
clojure.data.xml
与clojure.xml
不同。您可能需要浏览这两个库,以找到最适合您需要的库
您还可以在需要时使用crossclj.info
查找api文档:
更新:
在看到这个问题大约一周后,我遇到了一个XML解析问题,就像这个问题一样,需要unlazy
函数。你现在可以找到unlazy
Hmm。很有趣。谢谢你花时间澄清发生了什么。我不会把这称为对道尔的“免疫”;它似乎是另一种懒惰的东西,一种懒惰序列的懒惰序列。我还没有深入研究源代码,但它似乎是一种“懒惰映射”类型的结构,在datomic.query.EntityMap
中也可以看到。我认为问题在于doall
仅用于惰性序列,而不是“惰性映射”。
(ns tst.clj.core
(:use clj.core clojure.test tupelo.test)
(:require
[tupelo.core :as t]
[clojure.string :as str]
[clojure.pprint :refer [pprint]]
[clojure.java.io :as io]
[clojure.data.xml :as xml]
[clojure.walk :refer [postwalk]]
))
(t/refer-tupelo)
(defn unlazy
[coll]
(let [unlazy-item (fn [item]
(cond
(sequential? item) (vec item)
(map? item) (into {} item)
:else item))
result (postwalk unlazy-item coll) ]
result ))
(defn file->xml [path]
(with-open [rdr (-> path io/resource io/reader) ]
(let [lazy-vals (xml/parse rdr)
eager-vals (unlazy lazy-vals) ]
eager-vals)))
(pprint (file->xml "books.xml"))
{:tag :catalog,
:attrs {},
:content
[{:tag :book,
:attrs {:id "bk101"},
:content
[{:tag :author, :attrs {}, :content ["Gambardella, Matthew"]}
{:tag :title, :attrs {}, :content ["XML Developer's Guide"]}
{:tag :genre, :attrs {}, :content ["Computer"]}
{:tag :price, :attrs {}, :content ["44.95"]}
{:tag :publish_date, :attrs {}, :content ["2000-10-01"]}
{:tag :description,
:attrs {},
:content
["An in-depth look at creating applications\n with XML."]}]}
{:tag :book,
:attrs {:id "bk102"},
:content
[{:tag :author, :attrs {}, :content ["Ralls, Kim"]}
{:tag :title, :attrs {}, :content ["Midnight Rain"]}
{:tag :genre, :attrs {}, :content ["Fantasy"]}
{:tag :price, :attrs {}, :content ["5.95"]}
{:tag :publish_date, :attrs {}, :content ["2000-12-16"]}
{:tag :description,
:attrs {},
:content
["A former architect battles corporate zombies,\n an evil sorceress, and her own childhood to become queen\n of the world."]}]}
{:tag :book,
:attrs {:id "bk103"},
:content .....