XQuery IF-ELSE
XQuery If Then Else语句
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，并将其应用到包含if-then-else构造的XQuery表达式中，以检索价格大于100的那些书的书名。
XML语句M
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
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>30
return $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.java
import 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
将上述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。您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:
