快学Scala习题解答—第十六章 XML处理

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16.XML处理

16.1<fred/>(0) 得到什么？<fred/>(0)(0)呢？为什么？

回答：<fred/>(0) 得到一个scala.xml.Node，<fred/>(0)(0)也是得到scala.xml.Node。

因为scala.xml.Node 实现了方法 def apply(i: Int): Node，所以支持串接调用。

注意：scala-xml-x.x.x.jar 需要另外导入。

scala> val a = <fred/>a: scala.xml.Elem = <fred/>scala> a(0)res2: scala.xml.Node = <fred/>scala> a(0)(0)res3: scala.xml.Node = <fred/>scala> a(0)(0)(0)res4: scala.xml.Node = <fred/>scala> a(0)(0)(0)(0)res5: scala.xml.Node = <fred/>

16.2如下代码的值是什么？

<ul>

<li>Opening bracket: [</li>

<li>Closing bracket: ]</li>

<li>Opening brace: {</li>

<li>Closing brace: }</li>

</ul>

你如何修复它？

回答：会有编译错误。要在XML字面量中包含左花括号和右花括号，连续写两个即可。

package ex16_02import scala.xml._object Main extends App{/*Multiple markers at this line:in XML literal: in XML content, please use '}}' to express '}'I encountered a '}' where I didn't expect one, maybe this tag isn't closed <li>I encountered a '}' where I didn't expect one, maybe this tag isn't closed <li> */  val a =<ul>    <li>Opening bracket: [</li>    <li>Closing bracket: ]</li>       <li>Opening brace: {{</li>     <li>Closing brace: }}</li>   </ul>       println(a)}/*output:<ul>  <li>Opening bracket: [</li>  <li>Closing bracket: ]</li>     <li>Opening brace: {</li>     <li>Closing brace: }</li>   </ul>*/

16.3 比对 <li>Fred</li> match { case <li>{Text(t)}</li> => t } 和

<li>{"Fred"}</li> match { case <li>{Text(t)}</li> => t }

为什么它们的行为不同？

回答：内嵌表达式中的字符串并不会被转成Text节点而是Atom[String]节点。这和普通的Text节点还是有区别的——Text是Atom[String]的子类。

这对于保存文档没有问题。但如果你事后打算以Text节点的模式对它做匹配时，匹配会失败。像这种情况你应该插入Text节点而不是字符串。

import scala.xml._object Main extends App {  val a = <li>Fred</li> match { case <li>{ Text(t) }</li> => t }  //val b = <li>{ "Fred" }</li> match { case <li>{ Text(t) }</li> => t }  val c = <li>{ Text("Fred") }</li> match { case <li>{ Text(t) }</li> => t }  //println("a=" + a)  println("c=" + c)}/*output:a=Fredb: Exception in thread "main" scala.MatchError: <li>Fred</li> (of class scala.xml.Elem)c=Fred*/

16.4读取一个XHTML文件并打印所有不带alt属性的img元素。

import scala.xml._object Main extends App {  val root = XML.loadFile("./src/test.xhtml")  val imgs: NodeSeq = root \\ "img"  // img \ "@alt " 's type is scala.xml.NodeSeq  for (img <- imgs if (img \ "@alt").text == "") println(img)}/*output:<img src="hamster.jpg"/><img src="frog.jpg"/>*/

test.xhtml

<html><head><title>My Scala</title></head><body><p>Hello Scala</p><p><img src="hamster.jpg"/></p><p><img src="frog.jpg"/></p><p><img src="dog.jpg" alt="inu"/></p></body></html>

16.5打印XHTML文件中所有图像的名称。即，打印所有位�%@A�img元素内的src属性值。

import scala.xml._object Main extends App {  val root = XML.loadFile("./src/test.xhtml")  val imgs: NodeSeq = root \\ "img"  // img \ "@alt " 's type is scala.xml.NodeSeq  imgs.foreach { x => println(x \ "@src" text) }}/*output:hamster.jpgfrog.jpgdog.jpg*/

16.6读取XHTML文件并打印一个包含了文件中给出的所有超链接及其URL的表格。

即，打印所有a元素的child文本和href属性。

import scala.xml._object Main extends App {  val root = XML.loadFile("./src/oschina.xhtml")  val imgs: NodeSeq = root \\ "a"  imgs.foreach { x =>     val child = x.child    println("%s: %s".format(child(0).text, x.attribute("href").getOrElse("")))    }}/*output:Android: http://www.oschina.net/appiPhone: http://www.oschina.net/appWP7: http://www.oschina.net/app*/

oschina.xml:

<html><head><title>My Scala</title></head><body><p>Hello Scala</p><p><img src="hamster.jpg"/></p><p><img src="frog.jpg"/></p><p><img src="dog.jpg" alt="inu"/></p><ul><li><a href="http://www.oschina.net/app" class='android' title='Android客户端'>Android</a></li><li><a href="http://www.oschina.net/app" class='iphone' title='iPhone 客户端'>iPhone</a></li><li><a href="http://www.oschina.net/app" class='wp7' title='Windows Phone 客户端'>WP7</a></li></ul></body></html>

16.7编写一个函数，带一个类型为Map[String, String]的参数，返回一个dl元素，其中针对映射中每个键对应有一个dt，每个值对应有一个dd。例如：

Map("A" -> "1", "B" -> "2")

应产出 <dl><dt>A</dt><dd>1</dd><dt>B</dt><dd>2</dd></dl>

import scala.xml._object Main extends App { def genDl(input: Map[String,String])={   <dl>{for((k,v) <- input) yield <dt>{k}</dt><dd>{v}</dd>}</dl> }   val input = Map("A" -> "1", "B" -> "2") println(genDl(input))}/*output:<dl><dt>A</dt><dd>1</dd><dt>B</dt><dd>2</dd></dl>*/

16.8编写一个函数，接受dl元素，将它转成Map[String,String]。该函数应该是前一个练习中的反向处理，前提是所有dt后代都是唯一（各不相同）的。

import scala.xml._import scala.collection.mutable.Mapobject Main extends App {  def dl2map(input: scala.xml.Elem): Map[String, String] = {    val map = Map[String, String]()    val keys = input \ "dt"    val values = input \ "dd"    for (i <- 0 until keys.size) map += keys(i).text -> values(i).text    map  }  val input = <dl><dt>A</dt><dd>1</dd><dt>B</dt><dd>2</dd></dl>  val obj = dl2map(input)  println(obj)}/*output:Map(A -> 1, B -> 2)*/

16.9对一个XHTML文档进行变换，对所有不带alt属性的img元素添加一个alt="TODO"属性，其余内容完全不变。

import scala.xml._import scala.xml.transform._object Main extends App {  def transform(filename: String) {    val root = XML.loadFile(filename)    val rule1 = new RewriteRule {      override def transform(n: Node) = n match {        case x @ <img/> => if (x.attributes("alt") == null) x.asInstanceOf[Elem] % Attribute(null, "alt", "TODO", scala.xml.Null) else x        case _ => n      }    }    val transformed = new RuleTransformer(rule1).transform(root)    //println(transformed)    scala.xml.XML.save("./src/test_new.xhtml", transformed(0))  }  transform("./src/test.xhtml")}/*output:<html><head><title>My Scala</title></head><body><p>Hello Scala</p><p><img alt="TODO" src="hamster.jpg"/></p><p><img alt="TODO" src="frog.jpg"/></p><p><img alt="inu" src="dog.jpg"/></p></body></html>*/

16.10编写一个函数，读取XHTML文档，执行前一个练习中的变换，并保存结果。确保保存了DTD及所有CDATA内容。

import scala.xml._import scala.xml.transform._import scala.xml.parsing.ConstructingParserimport scala.xml.dtd._object Main extends App {  def transform(filename: String) {    val parser = ConstructingParser.fromFile(new java.io.File(filename), preserveWS = true)    val doc = parser.document    val root = doc.docElem    val rule1 = new RewriteRule {      override def transform(n: Node) = n match {        case x @ <img/> => if (x.attributes("alt") == null) x.asInstanceOf[Elem] % Attribute(null, "alt", "TODO", scala.xml.Null) else x        case _          => n      }    }    val transformed = new RuleTransformer(rule1).transform(root)    //println(transformed)    scala.xml.XML.save("./src/cdata_new.xhtml", transformed(0),      enc = "UTF-8",      xmlDecl = true,      doctype = DocType("html",        PublicID("-//W3C//DTD XHTML 1.0 Strict//EN",          "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"),        Nil))  }  transform("./src/cdata.xhtml")}/*output:<?xml version='1.0' encoding='UTF-8'?><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"><html><head><title>My Scala</title><script><![CDATA[function matchwo(a,b){if (a < b && a < 0) then  {  return 1;  }else  {  return 0;  }}]]></script></head><body><!-- This is a comment --><p>Hello Scala</p><p><img alt="TODO" src="hamster.jpg"/></p><p><img alt="TODO" src="frog.jpg"/></p><p><img alt="inu" src="dog.jpg"/></p></body></html>*/

原文博客地址:http://blog.csdn.net/u011225629/article/details/47618015

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