使用StaX解析XML遇到<p/>标签引发ClassCastException异常

Let’s break down exactly why you’re hitting this error and how to fix it:

The exception com.sun.xml.internal.stream.events.EndElementEvent cannot be cast to javax.xml.stream.events.Characters means your parsing code is trying to treat an XML end element (like </p> or the closing part of a self-closing <p/>) as text content. This happens when your logic assumes every <p> start tag is immediately followed by text, but encounters an empty (self-closing) <p/> tag where there’s no text to read.

How to Fix the Parsing Logic #

When using StAX (Streaming API for XML), you need to explicitly check the type of each event before casting or processing it. Here’s a corrected approach to safely parse your <p> elements:

import javax.xml.stream.XMLInputFactory;
import javax.xml.stream.XMLStreamConstants;
import javax.xml.stream.XMLStreamReader;
import java.io.StringReader;

public class XmlParser {
    public static void main(String[] args) throws Exception {
        String xml = "<body xmlns=\"http://www.w3.org/1999/xhtml\"> <p>GENE_ASSOCIATION: BLA BLA</p> <p>BLA BLA: Purine metabolism</p> <p>BLA BLA: 2.7.4.3</p> <p>BLA BLA Level: 1</p> <p>AUTHORS:PMID:6182143;PMID:624...</p> <p/> </body>";
        
        XMLInputFactory factory = XMLInputFactory.newInstance();
        XMLStreamReader reader = factory.createXMLStreamReader(new StringReader(xml));
        
        while (reader.hasNext()) {
            int eventType = reader.next();
            
            switch (eventType) {
                case XMLStreamConstants.START_ELEMENT:
                    if ("p".equals(reader.getLocalName())) {
                        StringBuilder content = new StringBuilder();
                        // Iterate until we hit the closing </p> tag
                        while (reader.hasNext()) {
                            int innerEventType = reader.next();
                            if (innerEventType == XMLStreamConstants.CHARACTERS) {
                                content.append(reader.getText());
                            } else if (innerEventType == XMLStreamConstants.END_ELEMENT) {
                                // We've reached the end of the <p> element
                                System.out.println("P content: " + content.toString().trim());
                                break;
                            }
                            // Add handling for other event types (like CDATA) if needed
                        }
                    }
                    break;
            }
        }
        reader.close();
    }
}

Key Changes to Avoid the Exception: #

• Check Event Types: Never assume the next event is text content—always verify it’s of type XMLStreamConstants.CHARACTERS before accessing text.
• Handle Empty Elements: The loop will gracefully exit when it hits the END_ELEMENT event, even for empty <p/> tags, avoiding invalid casts.
• Trim Whitespace: Using trim() ensures you don’t get empty strings from whitespace between tags.

Quick Note for Event-Based Parsers #

If you’re using XMLEventReader instead of XMLStreamReader, the same logic applies: check if the event is an instance of Characters before casting it.

内容的提问来源于stack exchange，提问作者ErEcTuS