JavaとXPathの完全ガイド！15のサンプルコードでマスター

import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathFactory;

public class XPathInitialization {
    public static void main(String[] args) {
        // XPathFactoryインスタンスの取得
        XPathFactory xPathFactory = XPathFactory.newInstance();

        // XPathインスタンスの生成
        XPath xPath = xPathFactory.newXPath();

        // 以降でxPathを使用してXMLファイルを操作
    }
}

<?xml version="1.0" encoding="UTF-8"?>
<bookstore>
    <book>
        <title lang="ja">Java入門</title>
        <price>3200</price>
    </book>
    <book>
        <title lang="en">Learn Java</title>
        <price>2500</price>
    </book>
</bookstore>

import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathFactory;
import org.w3c.dom.NodeList;
import org.xml.sax.InputSource;
import java.io.StringReader;

public class ElementRetrieval {
    public static void main(String[] args) {
        String xml = "（上記のXMLデータ）";  // XMLデータをここにコピー

        // XPathの初期設定
        XPathFactory xPathFactory = XPathFactory.newInstance();
        XPath xPath = xPathFactory.newXPath();

        try {
            // 日本語の書籍タイトルを取得
            String expression = "/bookstore/book/title[@lang='ja']";
            NodeList nodeList = (NodeList) xPath.evaluate(expression, new InputSource(new StringReader(xml)), XPathConstants.NODESET);

            for (int i = 0; i < nodeList.getLength(); i++) {
                System.out.println(nodeList.item(i).getTextContent());
            }

        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

// XPathの初期設定は前回のサンプルコード参照

public class RetrieveByAttribute {
    public static void main(String[] args) {
        String xml = "（上記のXMLデータ）";  // XMLデータは前の例と同じ
        try {
            // XPath式でlang属性が'en'のtitle要素を取得
            String expression = "/bookstore/book/title[@lang='en']";
            NodeList nodeList = (NodeList) xPath.evaluate(expression, new InputSource(new StringReader(xml)), XPathConstants.NODESET);

            // 結果の出力
            for (int i = 0; i < nodeList.getLength(); i++) {
                System.out.println(nodeList.item(i).getTextContent());
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

// XPathの初期設定は前回のサンプルコード参照

public class RetrieveByCondition {
    public static void main(String[] args) {
        String xml = "（上記のXMLデータ）";  // XMLデータは前の例と同じ
        try {
            // XPath式で価格が3000以上のbook要素を取得
            String expression = "/bookstore/book[price>=3000]/title";
            NodeList nodeList = (NodeList) xPath.evaluate(expression, new InputSource(new StringReader(xml)), XPathConstants.NODESET);

            // 結果の出力
            for (int i = 0; i < nodeList.getLength(); i++) {
                System.out.println(nodeList.item(i).getTextContent());
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

// ここでは既にXPathオブジェクトが作成されていると仮定します。
String xml = "<bookstore>..."; // XMLデータは事前に準備
String expression = "/bookstore/book[price>=3000]";
NodeList nodeList = (NodeList) xPath.evaluate(expression, new InputSource(new StringReader(xml)), XPathConstants.NODESET);

// 結果の処理
for (int i = 0; i < nodeList.getLength(); i++) {
    Element bookElement = (Element) nodeList.item(i);
    String title = bookElement.getElementsByTagName("title").item(0).getTextContent();
    String price = bookElement.getElementsByTagName("price").item(0).getTextContent();
    System.out.println("タイトル: " + title + ", 価格: " + price);
}

// XPathオブジェクトとXMLデータは前の例と同様
String expression = "/bookstore/book";
NodeList nodeList = (NodeList) xPath.evaluate(expression, new InputSource(new StringReader(xml)), XPathConstants.NODESET);

// 結果の加工と出力
StringBuilder report = new StringBuilder();
for (int i = 0; i < nodeList.getLength(); i++) {
    Element bookElement = (Element) nodeList.item(i);
    String title = bookElement.getElementsByTagName("title").item(0).getTextContent();
    String price = bookElement.getElementsByTagName("price").item(0).getTextContent();
    report.append("タイトル: ").append(title).append(", 価格: ").append(price).append("\n");
}
System.out.println("書籍情報のレポート:\n" + report);

import org.w3c.dom.*;
import javax.xml.parsers.*;
import javax.xml.xpath.*;
import javax.xml.transform.*;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;
import java.io.StringWriter;

// サンプルのXMLデータ
String xml = "<bookstore><book><title>初めてのJava</title><price>2500</price></book></bookstore>";

// XPathとDocumentオブジェクトの初期化
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
DocumentBuilder builder = factory.newDocumentBuilder();
Document doc = builder.parse(new InputSource(new StringReader(xml)));
XPathFactory xPathfactory = XPathFactory.newInstance();
XPath xpath = xPathfactory.newXPath();

// XPathで要素を特定
String expression = "/bookstore/book/title";
Node node = (Node) xpath.evaluate(expression, doc, XPathConstants.NODE);

// 要素のテキストを変更
node.setTextContent("Javaの極意");

// 変更をXMLに反映
TransformerFactory transformerFactory = TransformerFactory.newInstance();
Transformer transformer = transformerFactory.newTransformer();
StringWriter writer = new StringWriter();
transformer.transform(new DOMSource(doc), new StreamResult(writer));
String updatedXml = writer.getBuffer().toString();

// 変更後のXMLを出力
System.out.println(updatedXml);

// 前述のXPathとDocumentオブジェクトの初期化コードは省略

// 新しい要素を作成して追加
Element newElement = doc.createElement("author");
newElement.setTextContent("山田太郎");
XPathExpression expr = xpath.compile("/bookstore/book");
Node targetNode = (Node) expr.evaluate(doc, XPathConstants.NODE);
targetNode.appendChild(newElement);

// 価格要素を削除
String deleteExpression = "/bookstore/book/price";
Node deleteNode = (Node) xpath.evaluate(deleteExpression, doc, XPathConstants.NODE);
deleteNode.getParentNode().removeChild(deleteNode);

// 変更をXMLに反映（前の例と同様のコード）
// ここでは既にTransformerオブジェクトが作成されていると仮定
StringWriter writer2 = new StringWriter();
transformer.transform(new DOMSource(doc), new StreamResult(writer2));
String updatedXml2 = writer2.getBuffer().toString();

// 変更後のXMLを出力
System.out.println(updatedXml2);

import javax.xml.parsers.*;
import org.w3c.dom.*;
import javax.xml.xpath.*;
import java.io.StringReader;
import org.xml.sax.InputSource;

// サンプルのXMLデータ
String xml = "<bookstore>" +
             "<book><title>Java入門</title><price>2800</price></book>" +
             "<book><title>Python入門</title><price>3200</price></book>" +
             "<book><title>PHP入門</title><price>1900</price></book>" +
             "</bookstore>";

// Documentオブジェクトを作成
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
DocumentBuilder builder = factory.newDocumentBuilder();
Document doc = builder.parse(new InputSource(new StringReader(xml)));

// XPathオブジェクトを作成
XPathFactory xPathfactory = XPathFactory.newInstance();
XPath xpath = xPathfactory.newXPath();

// 複雑な条件で要素を抽出
String expression = "/bookstore/book[price >= 3000]/title";
NodeList nodeList = (NodeList) xpath.evaluate(expression, doc, XPathConstants.NODESET);

// 結果を出力
for (int i = 0; i < nodeList.getLength(); i++) {
    System.out.println(nodeList.item(i).getTextContent());
}

import javax.xml.xpath.*;
import javax.xml.parsers.*;
import org.w3c.dom.*;
import java.io.StringReader;
import org.xml.sax.InputSource;
import java.util.concurrent.*;

// サンプルのXMLデータ（ここでは短い例で説明）
String xml = "<employees>" +
             "<employee><id>1</id><name>田中</name></employee>" +
             "<employee><id>2</id><name>佐藤</name></employee>" +
             // ...（大量のデータ）...
             "</employees>";

// XPathとDocumentオブジェクトの作成
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
DocumentBuilder builder = factory.newDocumentBuilder();
Document doc = builder.parse(new InputSource(new StringReader(xml)));
XPathFactory xPathfactory = XPathFactory.newInstance();
XPath xpath = xPathfactory.newXPath();

// スレッドプールを作成
ExecutorService executor = Executors.newFixedThreadPool(4);

// 各スレッドで処理
String expression = "/employees/employee";
NodeList nodeList = (NodeList) xpath.evaluate(expression, doc, XPathConstants.NODESET);
for (int i = 0; i < nodeList.getLength(); i++) {
    int finalI = i;
    executor.submit(() -> {
        Node node = nodeList.item(finalI);
        // 何らかの処理（ここでは名前を出力）
        System.out.println(node.getTextContent());
    });
}
executor.shutdown();

import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathFactory;
import org.w3c.dom.Document;
import org.w3c.dom.NodeList;

// サンプルXML（特殊文字を含む）
String xml = "<items><item name='Apple &amp; Orange'>Fruit</item></items>";

DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
DocumentBuilder builder = factory.newDocumentBuilder();
Document doc = builder.parse(new ByteArrayInputStream(xml.getBytes()));

XPathFactory xPathfactory = XPathFactory.newInstance();
XPath xpath = xPathfactory.newXPath();

// XPathで特殊文字を含む要素を取得
String expression = "/items/item[@name='Apple &amp; Orange']";
NodeList nodeList = (NodeList) xpath.evaluate(expression, doc, XPathConstants.NODESET);

// 結果を出力
System.out.println(nodeList.item(0).getTextContent());

import org.apache.commons.lang3.StringEscapeUtils;

// 特殊文字を含む文字列
String specialStr = "Apple & Orange";

// エスケープ処理
String escapedStr = StringEscapeUtils.escapeXml11(specialStr);

// エスケープ後の文字列を使用してXMLを生成・処理
// ...

import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathFactory;
import org.w3c.dom.Document;
import org.w3c.dom.NodeList;

// XPathオブジェクトの初期化
XPathFactory xPathfactory = XPathFactory.newInstance();
XPath xpath = xPathfactory.newXPath();

// 効率的なXPathクエリ
String efficientExpression = "/items/item[1]";
NodeList efficientNodeList = (NodeList) xpath.evaluate(efficientExpression, doc, XPathConstants.NODESET);

import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathFactory;

// XPathFactoryの再利用
XPathFactory xPathfactory = XPathFactory.newInstance();
XPath xpath1 = xPathfactory.newXPath();
XPath xpath2 = xPathfactory.newXPath();

<dependencies>
  <dependency>
    <groupId>net.sf.saxon</groupId>
    <artifactId>Saxon-HE</artifactId>
    <version>9.9.1-7</version>
  </dependency>
</dependencies>

import net.sf.saxon.s9api.*;

// Saxonを用いたXPathのプロセッサー初期化
Processor processor = new Processor(false);
XPathCompiler compiler = processor.newXPathCompiler();

// XPath式のコンパイル
XPathExecutable executable = compiler.compile("/bookstore/book[price>30]/title");

// XMLソースの指定
DocumentBuilder builder = processor.newDocumentBuilder();
XdmNode doc = builder.build(new File("bookstore.xml"));

// XPathの評価
XPathSelector selector = executable.load();
selector.setContextItem(doc);
XdmValue value = selector.evaluate();