unexpected escaping when serializing objects with dom nodes

[potoo0]

full code:

package com.example;

import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.SerializationFeature;
import com.fasterxml.jackson.dataformat.xml.XmlMapper;
import com.fasterxml.jackson.module.jaxb.JaxbAnnotationModule;
import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.Test;
import org.w3c.dom.Element;
import org.w3c.dom.Node;

import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import javax.xml.bind.Marshaller;
import javax.xml.bind.annotation.XmlAccessType;
import javax.xml.bind.annotation.XmlAccessorType;
import javax.xml.bind.annotation.XmlAnyElement;
import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.transform.OutputKeys;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;
import java.io.ByteArrayInputStream;
import java.io.InputStream;
import java.io.StringWriter;
import java.nio.charset.StandardCharsets;

public class JacksonXmlIssueTest {
    private static final XmlMapper xmlMapper = buildXmlMapper();
    private static final JAXBContext jaxbContext = buildJAXBContext(RpcData.class);
    private static final TransformerFactory transformerFactory = buildTransformerFactory();

    @XmlRootElement(name = "data")
    @XmlAccessorType(XmlAccessType.FIELD)
    static class RpcData {
        public String name = "nameString";

        @XmlAnyElement
        public Element domElement;
    }

    @Test
    void testSer() throws Exception {
        String xml = "<L2VPN><VSIs>fake</VSIs></L2VPN>";
        // 1. parse string to dom
        DocumentBuilder db = DocumentBuilderFactory.newInstance().newDocumentBuilder();
        InputStream inputStream = new ByteArrayInputStream(xml.getBytes(StandardCharsets.UTF_8));
        Element element = db.parse(inputStream).getDocumentElement();
        Assertions.assertEquals(xml, transform(element));

        // 2.0 init javaBean
        RpcData rpcData = new RpcData();
        rpcData.domElement = element;

        // 2.1 test jaxb
        String xmlByJaxb = marshal(rpcData);
        System.out.println(xmlByJaxb);
        //<data><name>nameString</name><L2VPN><VSIs>fake</VSIs></L2VPN></data>

        // 2.2 test jackson-xml
        String xmlByJackson = xmlMapper.writeValueAsString(rpcData);
        System.out.println(xmlByJackson);
        //<data><name>nameString</name><domElement>&lt;L2VPN>&lt;VSIs>fake&lt;/VSIs>&lt;/L2VPN></domElement></data>
    }

    String marshal(Object data) throws JAXBException {
        Marshaller marshaller = jaxbContext.createMarshaller();
        marshaller.setProperty(Marshaller.JAXB_FRAGMENT, true);

        StringWriter sw = new StringWriter();
        marshaller.marshal(data, sw);
        return sw.toString();
    }

    String transform(Node node) throws Exception {
        Transformer transformer = transformerFactory.newTransformer();
        transformer.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "yes");
        transformer.setOutputProperty(OutputKeys.INDENT, "no");
        StreamResult result = new StreamResult(new StringWriter());
        transformer.transform(new DOMSource(node), result);
        return result.getWriter().toString();
    }

    static TransformerFactory buildTransformerFactory() {
        return TransformerFactory.newInstance();
    }

    static JAXBContext buildJAXBContext(Class clz) {
        try {
            return JAXBContext.newInstance(clz);
        } catch (JAXBException e) {
            throw new RuntimeException(e);
        }
    }

    static XmlMapper buildXmlMapper() {
        return XmlMapper.builder()
                .defaultUseWrapper(false)
                .serializationInclusion(JsonInclude.Include.NON_NULL)
                .addModule(new JaxbAnnotationModule())
                .disable(SerializationFeature.WRAP_ROOT_VALUE)
                .disable(DeserializationFeature.UNWRAP_ROOT_VALUE)
                .build();
    }
}

jaxb doesn't have the weird < escape, but jackson-xml has, how to fix it? output:

# xmlByJaxb
<data><name>nameString</name><L2VPN><VSIs>fake</VSIs></L2VPN></data>

# xmlByJackson
<data><name>nameString</name><domElement>&lt;L2VPN>&lt;VSIs>fake&lt;/VSIs>&lt;/L2VPN></domElement></data>

[pjfanning]

• public Element domElement; is serialized as an element with escaped text by jackson-dataformat-xml
• JAXB seems to serialize the dom element as an embedded XML structure
• both approaches are valid encodings
• if you don't like jackson-dataformat-xml's solution, you can stick with JAXB - or you can write your own custom Jackson serializer

[potoo0]

• public Element domElement; is serialized as an element with escaped text by jackson-dataformat-xml
• JAXB seems to serialize the dom element as an embedded XML structure
• both approaches are valid encodings
• if you don't like jackson-dataformat-xml's solution, you can stick with JAXB - or you can write your own custom Jackson serializer

In fact, < escape is do not fit my need here, cannot be parsed by the netconf server。

[pjfanning]

Still not a bug in a jackson-dataformat-xml. It is possible that jackson-dataformat-xml has a configuration that gets it to behave like you need but I am not aware of it. You still have the option to use another library (ie stop using jackson-dataformat-xml) or to write a custom Jackson serializer for the Element class and register it in ObjectMapper.

[potoo0]

thx. just replace g.writeString(result.getWriter().toString()); with

g.writeRaw(result.getWriter().toString());
ToXmlGenerator toXmlGenerator = (ToXmlGenerator) g;
toXmlGenerator.setNextIsUnwrapped(true);
g.writeNull();

fit my needs.

full code:

package com.example.netconf;

import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.databind.JavaType;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.SerializerProvider;
import com.fasterxml.jackson.databind.jsonFormatVisitors.JsonFormatVisitorWrapper;
import com.fasterxml.jackson.databind.ser.std.StdSerializer;
import com.fasterxml.jackson.dataformat.xml.ser.ToXmlGenerator;
import org.w3c.dom.Node;

import javax.xml.XMLConstants;
import javax.xml.transform.*;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;
import java.io.IOException;
import java.io.StringWriter;

/**
 * serialize the dom element as an embedded XML structure.<br>
 * todo: <br>
 *  1. deserialize an embedded XML structure<br>
 *  2. fix dom.Node direct serializer<br>
 **/
@SuppressWarnings("serial")
public class DOMEmbeddedSerializer extends StdSerializer<Node> {
    protected final TransformerFactory transformerFactory;

    public DOMEmbeddedSerializer() {
        super(Node.class);
        try {
            transformerFactory = TransformerFactory.newInstance();
            transformerFactory.setFeature(XMLConstants.FEATURE_SECURE_PROCESSING, true);
        } catch (Exception e) {
            throw new IllegalStateException("Could not instantiate `TransformerFactory`: " + e.getMessage(), e);
        }
    }

    @Override
    public void serialize(Node value, JsonGenerator g, SerializerProvider provider)
            throws IOException {
        try {
            Transformer transformer = transformerFactory.newTransformer();
            transformer.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "yes");
            transformer.setOutputProperty(OutputKeys.INDENT, "no");
            StreamResult result = new StreamResult(new StringWriter());
            transformer.transform(new DOMSource(value), result);
            g.writeRaw(result.getWriter().toString());
            // todo: will throw an error(`document has no root (ie. trying to output empty document)`)
            //      if dom.Node direct serializer
            ToXmlGenerator toXmlGenerator = (ToXmlGenerator) g;
            toXmlGenerator.setNextIsUnwrapped(true);
            g.writeNull();
        } catch (TransformerConfigurationException e) {
            throw new IllegalStateException("Could not create XML Transformer for writing DOM `Node` value: " + e.getMessage(), e);
        } catch (TransformerException e) {
            provider.reportMappingProblem(e, "DOM `Node` value serialization failed: %s", e.getMessage());
        }
    }

    @Override
    public JsonNode getSchema(SerializerProvider provider, java.lang.reflect.Type typeHint) {
        // Well... it is serialized as String
        return createSchemaNode("string", true);
    }

    @Override
    public void acceptJsonFormatVisitor(JsonFormatVisitorWrapper visitor, JavaType typeHint) throws JsonMappingException {
        if (visitor != null) visitor.expectAnyFormat(typeHint);
    }
}

[cowtowncoder]

@potoo0 Thank you for sharing this trick! That makes sense and could be useful for others who want to forcibly embed pre-encoded content. There are some possible challenges with it, but it probably works for many cases.

One other idea: given the work-around (which by-passes serialization), I wonder if use of @JsonRawValue would work? It should do about the same thing (just replace @XmlElement with @JsonRawValue -- "json" here doesn't mean format is JSON)

[potoo0]

@potoo0 Thank you for sharing this trick! That makes sense and could be useful for others who want to forcibly embed pre-encoded content. There are some possible challenges with it, but it probably works for many cases.

One other idea: given the work-around (which by-passes serialization), I wonder if use of @JsonRawValue would work? It should do about the same thing (just replace @XmlElement with @JsonRawValue -- "json" here doesn't mean format is JSON)

@JsonRawValue not work, JsonRawValue call .toString not xml string. JsonRawValue code:

/**
 * This is a simple dummy serializer that will just output raw values by calling
 * toString() on value to serialize.
 */
@SuppressWarnings("serial")
public class RawSerializer<T>
    extends StdSerializer<T>
{
    // ....................
    @Override
    public void serialize(T value, JsonGenerator jgen, SerializerProvider provider) throws IOException {
        jgen.writeRawValue(value.toString());
    }
    // ....................
}

[cowtowncoder]

Ah ok. Makes sense; Element.toString() does not produce valid XML output.

Thank you for verifying this, @potoo0 . So to use that annotation, one would need to use a wrapper type that implemented serialization similar to code you showed earlier.

[potoo0]

share a simple serializer for dynamic xml attr from map:

/**
 * serialize map as xml attribute.<br>
 * 注意: 配合 {@code @JsonInclude(value = JsonInclude.Include.NON_EMPTY)}
 * 或者 {@code @JacksonXmlProperty(isAttribute = true)}, 防止 value=null 时错误序列化
 *
 * <p>
 * 用法:
 * <pre>{@code
 *   // 不要直接注册到 mapper 里, 应该在字段上使用
 *   class Srv {
 *      @JacksonXmlProperty(isAttribute = true)
 *      @JsonSerialize(using = DynaXmlAttributeSerializer.class)
 *      Map<String, String> attrs;
 *
 *      @JsonInclude(value = JsonInclude.Include.NON_EMPTY)
 *      @JsonSerialize(using = DynaXmlAttributeSerializer.class)
 *      Map<String, String> attrsOther;
 *   }
 * }</pre>
 * </p>
 **/
public class DynaXmlAttributeSerializer extends StdSerializer<Map<Object, Object>> {
    protected DynaXmlAttributeSerializer() {
        super(Map.class, true);
    }

    @Override
    public void serialize(Map<Object, Object> value, JsonGenerator g, SerializerProvider provider) throws IOException {
        if (!(g instanceof ToXmlGenerator)) throw new RuntimeException("only support xml!");
        ToXmlGenerator xgen = (ToXmlGenerator) g;
        xgen.setNextIsUnwrapped(true);
        xgen.writeNull();
        // 防止额外使用 `@JacksonXmlProperty(isAttribute = true)` 注解后导致下个字段被错误 Unwrap. 疑问: writeNull 没有清空???
        xgen.setNextIsUnwrapped(false);
        if (value == null || value.isEmpty()) return;
        xgen.setNextIsAttribute(true);
        for (Map.Entry<Object, Object> entry : value.entrySet()) {
            if (entry.getKey() == null || entry.getValue() == null) continue;
            xgen.writeStringField(entry.getKey().toString(), entry.getValue().toString());
        }
        xgen.setNextIsAttribute(false);
    }
}

example:

class A {
    @JacksonXmlProperty(isAttribute = true)
    public String name = "Rick";

    @JsonSerialize(using = DynaXmlAttributeSerializer.class)
    public Map<Object, Object> attrs = ImmutableMap.of("k1","v1", "xmlns:xc", "h3c");
}
// serialize output
// <A name="Rick" k1="v1" xmlns:xc="h3c"/>