XQuery If Then Else语句 _XQuery

本文概述

XQuery If Then else示例
对XML执行XQuery

XQuery If Then Else语句用于检查传递的输入值的有效性。

if (condition) then ... else ...

XQuery If Then else示例让我们以一个示例来演示XQuery中if-then-else语句的用法。取一个名为books.xml的XML文件, 并对其应用XQuery表达式, 该表达式包含if-then-else构造, 以检索价格大于100的那些书的书名。
XML陈述式
books.xml

< ?xml version="1.0" encoding="UTF-8"?> < books> < book category="JAVA"> < title lang="en"> Learn Java Programming< /title> < author> Sonoo Jaiswal< /author> < year> 2012< /year> < price> 400.00< /price> < /book> < book category="DOTNET"> < title lang="en"> DOTNET Fun< /title> < author> Balaswamy< /author> < year> 2008< /year> < price> 300.50< /price> < /book> < book category="XML"> < title lang="en"> Learn XQuery in 1 month< /title> < author> Ajeet Kumar< /author> < author> Sam Lee< /author> < year> 2013< /year> < price> 250.00< /price> < /book> < book category="XML"> < title lang="en"> Learn XPath in 1 month< /title> < author> Ajeet Kumar< /author> < year> 2014< /year> < price> 150.50< /price> < /book> < /books>

XQuery表达式
【XQuery If Then Else语句】books.xqy：

< result> {if(not(doc("books.xml"))) then (< error> < message> books.xml does not exist< /message> < /error> )else ( for $x in doc("books.xml")/books/book where $x/price> 30return $x/title)}< /result> Create a Java based XQuery executor program to read the books.xqy, passes it to the XQuery expression processor, and executes the expression. After that the result will be displayed. XQueryTester.javaimport java.io.File; import java.io.FileInputStream; import java.io.FileNotFoundException; import java.io.InputStream; import javax.xml.xquery.XQConnection; import javax.xml.xquery.XQDataSource; import javax.xml.xquery.XQException; import javax.xml.xquery.XQPreparedExpression; import javax.xml.xquery.XQResultSequence; import com.saxonica.xqj.SaxonXQDataSource; public class XQueryTester {public static void main(String[] args){try {execute(); }catch (FileNotFoundException e) {e.printStackTrace(); }catch (XQException e) {e.printStackTrace(); }}private static void execute() throws FileNotFoundException, XQException{InputStream inputStream = new FileInputStream(new File("books.xqy")); XQDataSource ds = new SaxonXQDataSource(); XQConnection conn = ds.getConnection(); XQPreparedExpression exp = conn.prepareExpression(inputStream); XQResultSequence result = exp.executeQuery(); while (result.next()) {System.out.println(result.getItemAsString(null)); }} }

对XML执行XQuery 将以上三个文件放在同一位置。我们将它们放在桌面上的文件夹名称XQuery9中。使用控制台编译XQueryTester.java。你必须在计算机上安装JDK 1.5或更高版本, 并且已配置类路径。
编译：
javac XQueryTester.java
执行：
Java XQueryTester
输出