Pretty printing XML with Jackson library

Question

I am trying to use Jackson library to serialize Java objects into XML by using JAXB annotations. However, I face an issue in pretty-printing the XML output.

Here is my sample code usage:

ObjectMapper mapper = new XmlMapper();
mapper.enable(SerializationFeature.INDENT_OUTPUT);
String xml = mapper.writeValueAsString(person);

And, I'm seeing the below exception. The issue here is Jackson uses Stax2Writer as XML writer and Stax2 doesn't seem to support writing raw strings (in this case DefaultPrettyPrinter tries to write "\n" as raw string).

    com.fasterxml.jackson.databind.JsonMappingException: Not implemented (through reference chain: xml.serialization.jackson.dto.Person["name"])
    at com.fasterxml.jackson.databind.JsonMappingException.wrapWithPath(JsonMappingException.java:232)
    at com.fasterxml.jackson.databind.JsonMappingException.wrapWithPath(JsonMappingException.java:197)
    at com.fasterxml.jackson.databind.ser.std.StdSerializer.wrapAndThrow(StdSerializer.java:187)
    at com.fasterxml.jackson.dataformat.xml.ser.XmlBeanSerializer.serializeFields(XmlBeanSerializer.java:174)
    at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:152)
    at com.fasterxml.jackson.dataformat.xml.ser.XmlSerializerProvider.serializeValue(XmlSerializerProvider.java:92)
    at com.fasterxml.jackson.databind.ObjectMapper._configAndWriteValue(ObjectMapper.java:2818)
    at com.fasterxml.jackson.databind.ObjectMapper.writeValueAsString(ObjectMapper.java:2275)
    at xml.serialization.jackson.SerializationTest.main(SerializationTest.java:46)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:120)
Caused by: java.lang.UnsupportedOperationException: Not implemented
    at org.codehaus.stax2.ri.Stax2WriterAdapter.writeRaw(Stax2WriterAdapter.java:380)
    at org.codehaus.stax2.ri.Stax2WriterAdapter.writeRaw(Stax2WriterAdapter.java:373)
    at com.fasterxml.jackson.dataformat.xml.util.DefaultXmlPrettyPrinter$Lf2SpacesIndenter.writeIndentation(DefaultXmlPrettyPrinter.java:498)
    at com.fasterxml.jackson.dataformat.xml.util.DefaultXmlPrettyPrinter.writeLeafElement(DefaultXmlPrettyPrinter.java:271)
    at com.fasterxml.jackson.dataformat.xml.ser.ToXmlGenerator.writeString(ToXmlGenerator.java:489)
    at com.fasterxml.jackson.databind.ser.std.StringSerializer.serialize(StringSerializer.java:39)
    at com.fasterxml.jackson.databind.ser.std.StringSerializer.serialize(StringSerializer.java:21)
    at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:541)
    at com.fasterxml.jackson.dataformat.xml.ser.XmlBeanSerializer.serializeFields(XmlBeanSerializer.java:161)
    ... 10 more

Any thoughts on how to work it around?

Answer 1

According to the Stax2WriterAdapter's documentation thier default implementation is incomplete. Also comments in the code say that the writeRaw() method cannot be implemented using Stax 1.0 which is default for Java runtime.

You should switch to use a Stax2 library as suggested on this wiki page.

After I added the following Maven dependency to my project, the example below started to work as expected:

<dependency>
    <groupId>org.codehaus.woodstox</groupId>
    <artifactId>woodstox-core-asl</artifactId>
    <version>4.1.4</version>
</dependency>

Code example:

public class JacksonXmlMapper {
    public static class Person {
        final public String name;

        public Person(String name) {
            this.name = name;
        }
    }

    public static void main(String[] args) throws JsonProcessingException {
        ObjectMapper mapper = new XmlMapper();
        mapper.enable(SerializationFeature.INDENT_OUTPUT);
        System.out.println(mapper.writeValueAsString(new Person("John")));
    }
}

Output:

<Person>
   <name>John</name>
</Person>