Read from Stax XMLStreamReader to unmarshall partial

Question

Im working with the Stax cursor api to extract data from large xml files. Current I go to the beginning of a special tag and unmarshall the tag with JAXB. That works fine on well formed xml files. But not a long time ago I had a document in which one of hundreds of thousands tags was not closed. JAXB steped with the XMLStreamReader until the end of the document and failed. Is there a way to read from a beginning tag to a closing tag and unmarshall this separate? So I would lose two tags with Exception and not the rest of the document. The only way I found was to use a normal BufferedReader instead of the XMLStreamReader and check the line content. But that solution seems to me ugly.

Answer 1

I've had reasonable success using jackson to deserialise XML fragments. When individual reads fail the process can be recovered by advancing the cursor to the next fragment:

import com.fasterxml.jackson.dataformat.xml.XmlMapper;

import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.stream.XMLInputFactory;
import javax.xml.stream.XMLStreamConstants;
import javax.xml.stream.XMLStreamException;
import javax.xml.stream.XMLStreamReader;
import java.io.StringReader;

public class XmlFragmentReader {
    public static void main(String[] args) throws XMLStreamException {
        String xml =
            "<list>\n" +
            "<object><name>a</name></object>\n" +
            "<object><name>b</name>\n" + // Missing closing tag
            "<object><name>c</name></object>\n" +
            "<object><name>d</name></object>\n" +
            "<object><name>e</name></object>\n" +
            "</list>";

        XMLStreamReader reader = XMLInputFactory
            .newInstance()
            .createXMLStreamReader(new StringReader(xml));

        XmlMapper mapper = new XmlMapper();
        while (next(reader, "object")) {
            try {
                Obj obj = mapper.readValue(reader, Obj.class);
                System.out.println("Read: " + obj.getName());
            } catch (Exception e) {
                System.err.println("Read Failed: " + e);
            }
        }
    }

    // Advance cursor to the opening tag <name>
    private static boolean next(XMLStreamReader reader, String name) throws XMLStreamException {
        while (true) {
            if (reader.getEventType() == XMLStreamConstants.START_ELEMENT && reader.getLocalName().equals(name)) {
                return true;
            } else if (!reader.hasNext()) {
                return false;
            }
            reader.next();
        }
    }

    // Test object
    @XmlRootElement(name = "object")
    public static class Obj {
        private String name;

        @XmlElement
        public String getName() {
            return name;
        }

        public void setName(String name) {
            this.name = name;
        }
    }
}

Output:

Read a
Read d
Read e