feat(#213): Add ugly working solution

src/main/java/com/jcabi/xml/SaxonDocument.java

@@ -0,0 +1,97 @@
+/*
+ * Copyright (c) 2012-2022, jcabi.com
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met: 1) Redistributions of source code must retain the above
+ * copyright notice, this list of conditions and the following
+ * disclaimer. 2) Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following
+ * disclaimer in the documentation and/or other materials provided
+ * with the distribution. 3) Neither the name of the jcabi.com nor
+ * the names of its contributors may be used to endorse or promote
+ * products derived from this software without specific prior written
+ * permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT
+ * NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
+ * THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
+ * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+package com.jcabi.xml;
+
+import java.io.StringReader;
+import java.util.List;
+import java.util.stream.Collectors;
+import javax.xml.namespace.NamespaceContext;
+import javax.xml.transform.stream.StreamSource;
+import net.sf.saxon.s9api.DocumentBuilder;
+import net.sf.saxon.s9api.Processor;
+import net.sf.saxon.s9api.SaxonApiException;
+import net.sf.saxon.s9api.XPathCompiler;
+import net.sf.saxon.s9api.XPathExecutable;
+import net.sf.saxon.s9api.XPathSelector;
+import net.sf.saxon.s9api.XdmItem;
+import net.sf.saxon.s9api.XdmNode;
+import net.sf.saxon.s9api.XdmValue;
+import org.w3c.dom.Node;
+
+public class SaxonDocument implements XML {
+
+    private final String text;
+
+    /**
+     * Public constructor from XML as string text.
+     *
+     * @param text XML document body.
+     */
+    public SaxonDocument(final String text) {
+        this.text = text;
+    }
+
+    @Override
+    public List<String> xpath(final String query) {
+        Processor processor = new Processor(false);
+        try {
+            DocumentBuilder builder = processor.newDocumentBuilder();
+            XdmNode doc = builder.build(new StreamSource(new StringReader(text)));
+            XPathCompiler xpathCompiler = processor.newXPathCompiler();
+            XPathExecutable xpathExec = xpathCompiler.compile(query);
+            XPathSelector selector = xpathExec.load();
+            selector.setContextItem(doc);
+            XdmValue result = selector.evaluate();
+            return result.stream().map(XdmItem::getStringValue).collect(Collectors.toList());
+        } catch (SaxonApiException ex) {
+            throw new RuntimeException(ex);
+        }
+    }
+
+    @Override
+    public List<XML> nodes(final String query) {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public XML registerNs(final String prefix, final Object uri) {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public XML merge(final NamespaceContext context) {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public Node node() {
+        throw new UnsupportedOperationException();
+    }
+}

src/test/java/com/jcabi/xml/SaxonDocumentTest.java

@@ -0,0 +1,19 @@
+package com.jcabi.xml;
+
+import org.hamcrest.MatcherAssert;
+import org.hamcrest.Matchers;
+import org.junit.jupiter.api.Test;
+
+class SaxonDocumentTest {
+
+    @Test
+    void findsXpathWithFunctionThatReturnsSeveralItems() {
+        MatcherAssert.assertThat(
+            "XMLDocument can handle XPath 2.0 feature - XPath evaluation of concat method, but it can't",
+            new SaxonDocument(
+                "<o><o base='a' ver='1'/><o base='b' ver='2'/></o>"
+            ).xpath("//o[@base and @ver]/concat(@base,'|',@ver)"),
+            Matchers.hasItems("a|1", "b|2")
+        );
+    }
+}