Java使用XPath提取XML节点并封装为自定义类列表的优化方法

方案1：基于单游戏节点上下文查询（易读性优先） #

不需要每次都从根节点扫描整个文档，直接以遍历到的每个游戏节点为上下文执行相对路径查询，虽然还是3次XPath调用，但都是在当前节点的子节点中查询，性能远高于原有的全文档扫描，而且代码逻辑清晰不易出错。

首先定义你需要的Probability类：

public class Probability {
    private double team1WinPerc;
    private double team2WinPerc;
    private double drawPerc;

    // 构造方法
    public Probability(double team1WinPerc, double team2WinPerc, double drawPerc) {
        this.team1WinPerc = team1WinPerc;
        this.team2WinPerc = team2WinPerc;
        this.drawPerc = drawPerc;
    }

    // 按需添加getter、setter方法
}

优化后的业务代码：

final DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
final DocumentBuilder db = dbf.newDocumentBuilder();
final Document document = db.parse(new InputSource(
        new ByteArrayInputStream(xmlResponseString.getBytes(StandardCharsets.UTF_8))));

final XPathFactory xpathFactory = XPathFactory.newInstance();
final XPath xpath = xpathFactory.newXPath();

// 拿到所有游戏节点
NodeList gameNodes = (NodeList) xpath.evaluate("stats/games/*", document, XPathConstants.NODESET);
List<Probability> probabilityList = new ArrayList<>(gameNodes.getLength());

for (int i = 0; i < gameNodes.getLength(); i++) {
    Node gameNode = gameNodes.item(i);
    // 直接在当前游戏节点下查询相对路径，不需要拼接节点名
    double team1Win = Double.parseDouble(xpath.evaluate("team1_win_perc", gameNode, XPathConstants.STRING));
    double team2Win = Double.parseDouble(xpath.evaluate("team2_win_perc", gameNode, XPathConstants.STRING));
    double draw = Double.parseDouble(xpath.evaluate("draw_perc", gameNode, XPathConstants.STRING));
    probabilityList.add(new Probability(team1Win, team2Win, draw));
}

方案2：单次XPath查询所有目标节点（性能优先） #

如果你需要彻底避免多次XPath调用，可以直接写一个XPath表达式一次性取出所有游戏的三个百分比节点，每三个节点为一组对应一个游戏的三个值，全程只执行一次XPath评估：

final DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
final DocumentBuilder db = dbf.newDocumentBuilder();
final Document document = db.parse(new InputSource(
        new ByteArrayInputStream(xmlResponseString.getBytes(StandardCharsets.UTF_8))));

final XPathFactory xpathFactory = XPathFactory.newInstance();
final XPath xpath = xpathFactory.newXPath();

// 一次性查询所有游戏下的三个百分比节点，顺序和XML中节点顺序一致
NodeList percNodes = (NodeList) xpath.evaluate("stats/games/*/team1_win_perc | stats/games/*/team2_win_perc | stats/games/*/draw_perc", 
        document, XPathConstants.NODESET);
List<Probability> probabilityList = new ArrayList<>();

// 每三个节点对应一个游戏的三个值
for (int i = 0; i < percNodes.getLength(); i += 3) {
    double team1Win = Double.parseDouble(percNodes.item(i).getTextContent());
    double team2Win = Double.parseDouble(percNodes.item(i+1).getTextContent());
    double draw = Double.parseDouble(percNodes.item(i+2).getTextContent());
    probabilityList.add(new Probability(team1Win, team2Win, draw));
}

注意：该方案依赖XML中每个游戏节点下的三个百分比节点顺序固定为team1_win_perc -> team2_win_perc -> draw_perc，如果你的XML结构顺序可能变化，推荐使用方案1。

内容的提问来源于stack exchange，提问作者clattenburg cake