Java SAX DefaultHandler 解析获取具有多个同名标签的标签值

Question

我有这个输入 XML:

<REQUEST>
    <ELEMENT>element inside request</ELEMENT>
    <NUMBER>250</NUMBER>
    <LIST>
          <ELEMENT>element inside list</ELEMENT>
          <LETTER>A</LETTER>
    </LIST>
    <OTHER1>other 1</OTHER1>
</REQUEST>

我正在 class 中扩展 DefaultHandler，我用它来获取值。

这是我的 class:

public class MyHandler extends DefaultHandler {
    private String elementName = null;
    private boolean bElement = false;

    private String element = null;

    @Override
    public void characters(char[] ch, int start, int length) throws SAXException {
        if (bElement){
            elementName = new String(ch, start, length);
        }
    }

    @Override
    public void endElement(String uri, String localName, String qName) throws SAXException {
        if("ELEMENT".equalsIgnoreCase(qName) && elementName == null){
            element = elementName;
        }
        bElement = false;
    }

    @Override
    public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException {
        if(qName.equalsIgnoreCase("ELEMENT")){
            bElement = true;
        }
    }

    public String getElement() {
        return this.element;
    }

}

我有这个逻辑来获取元素值（请求是一个 HttpServletRequest）：

ByteArrayOutputStream baos = new ByteArrayOutputStream();
byte[] buf = new byte[1024];
int n = 0;
while ((n = request.getInputStream().read(buf)) >= 0) {
    baos.write(buf, 0, n);
}
byte[] content = baos.toByteArray();
SAXParserFactory factory = SAXParserFactory.newInstance();
SAXParser saxParser = factory.newSAXParser();
MyHandler handler = new MyHandler();
saxParser.parse(new ByteArrayInputStream(content), handler);
return handler.getElement();

当我发送上面的XML时，我们得到了REQUEST->LIST->ELEMENT里面的值，所以我得到了String:

element inside list

但我想先获取里面的字符串 ELEMENT 标签

element inside request

我需要完成 MyHandler class 中的代码以获取 中的 ELEMENT 值REQUEST->ELEMENT 并且没有得到另一个 ELEMENT.

Answer 1

您需要跟踪 XML 中的完整位置。

注意 - 这是完全未经测试的代码。

public class MyHandler extends DefaultHandler {

    // Use a DEQUE to track the current position inthe xml.
    private Deque<String> position = new ArrayDeque<>();
    // My data.
    private StringBuilder data = new StringBuilder();

    private String element = null;

    @Override
    public void characters(char[] ch, int start, int length) throws SAXException {
        if (match()) {
            // Append to my buffer.
            data.append(ch, start, length);
        }
    }

    @Override
    public void endElement(String uri, String localName, String qName) throws SAXException {
        // Ending a tag - pop it from end.
        position.removeLast();
    }

    @Override
    public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException {
        // Starting a tag - push it at the end.
        position.addLast(qName);
    }

    public String getElement() {
        return this.element;
    }

    // Specifically looking for the REQUEST.ELEMENT - not the REQUEST.LIST.ELEMENT
    private final String[] lookingFor = {"REQUEST", "ELEMENT"};

    private boolean match() {
        // Must be that deep.
        if (position.size() == lookingFor.length) {
            // Must match.
            Iterator<String> match = position.iterator();
            for (int i = 0; i < lookingFor.length; i++) {
                // Match?
                if (!match.next().equals(lookingFor[i])) {
                    return false;
                }
            }
        } else {
            // Wrong depth.
            return false;
        }
        // No mismatch -> match!
        return true;
    }

}

此外 - 顺便说一句，当调用 characters 时，您应该始终 append。

Java SAX DefaultHandler 解析获取具有多个同名标签的标签值

Java SAX DefaultHandler parsing get tag value with several tags with the same name

java

sax

xml-parsing