Deserializing List<Serializable> object fails - using Spring 4.2.4 RestController and Jackson 2.5.4

[Luke Rahl]

Deserializing List<Serializable> object fails - using Spring 4.2.4 RestController and Jackson 2.5.4.

I get the following error:

Unexpected failure: Could not read document: Can not construct instance of java.io.Serializable, problem: abstract types either need to be mapped to concrete types, have custom deserializer, or be instantiated with additional type information\n at [Source: java.io.PushbackInputStream@408725ba; line: 1, column: 3071] (through reference chain: gov.sandia.generated.entities.eacontent.Ea[\"commonSections\"]->gov.sandia.generated.entities.eacontent.CommonSections[\"purpose\"]->gov.sandia.generated.entities.eacontent.Purpose[\"releaseReason\"]->java.util.ArrayList[0]->gov.sandia.generated.entities.eacontent.ReleaseReason[\"paragraph\"]->java.util.ArrayList[0]->gov.sandia.generated.entities.eacontent.Paragraph[\"content\"]->java.util.ArrayList[0]); nested exception is com.fasterxml.jackson.databind.JsonMappingException: Can not construct instance of java.io.Serializable, problem: abstract types either need to be mapped to concrete types, have custom deserializer, or be instantiated with additional type information\n at [Source: java.io.PushbackInputStream@408725ba; line: 1, column: 3071] (through reference chain: gov.sandia.generated.entities.eacontent.Ea[\"commonSections\"]->gov.sandia.generated.entities.eacontent.CommonSections[\"purpose\"]->gov.sandia.generated.entities.eacontent.Purpose[\"releaseReason\"]->java.util.ArrayList[0]->gov.sandia.generated.entities.eacontent.ReleaseReason[\"paragraph\"]->java.util.ArrayList[0]->gov.sandia.generated.entities.eacontent.Paragraph[\"content\"]->java.util.ArrayList[0])

Code for Paragraph:

package def.com.generated.entities.eacontent;

import java.io.Serializable;

import java.util.ArrayList;

import java.util.List;

import javax.xml.bind.JAXBElement;

import javax.xml.bind.annotation.XmlAccessType;

import javax.xml.bind.annotation.XmlAccessorType;

import javax.xml.bind.annotation.XmlAttribute;

import javax.xml.bind.annotation.XmlElementRef;

import javax.xml.bind.annotation.XmlMixed;

import javax.xml.bind.annotation.XmlType;

@XmlAccessorType(XmlAccessType.FIELD)
@XmlType(name = "paragraph", propOrder = {
    "content"
})
public class Paragraph implements Serializable
{


    private final static long serialVersionUID = -1L;
    @XmlElementRef(name = "paragraph", namespace = "http://def.com/ea/schemas", type = JAXBElement.class, required = false)
    @XmlMixed @org.mongodb.morphia.annotations.Serialized
    protected List<Serializable> content;
    @XmlAttribute(name = "ea-revision", required = true)
    protected String eaRevision;
    @XmlAttribute(name = "href")
    protected String href;
    @XmlAttribute(name = "id")
    protected String id;
    @XmlAttribute(name = "sequence")
    protected String sequence;
    @XmlAttribute(name = "para-status")
    protected ParaStatus paraStatus;


    /**
     * Default no-arg constructor
     *
     */
    public Paragraph() {
        super();
    }


    public Paragraph(final List<Serializable> content, final String eaRevision, final String href, final String id, final String sequence, final ParaStatus paraStatus) {
        this.content = content;
        this.eaRevision = eaRevision;
        this.href = href;
        this.id = id;
        this.sequence = sequence;
        this.paraStatus = paraStatus;
    }


    public List<Serializable> getContent() {
        if (content == null) {
            content = new ArrayList<Serializable>();
        }
        return this.content;
    }


    public String getEaRevision() {

        return eaRevision;
    }


    public void setEaRevision(String value) {

        this.eaRevision = value;
    }


    public String getHref() {

        return href;
    }


    public void setHref(String value) {

        this.href = value;
    }


    public String getId() {

        return id;
    }


    public void setId(String value) {

        this.id = value;
    }


    public String getSequence() {

        return sequence;
    }


    public void setSequence(String value) {

        this.sequence = value;
    }


    public ParaStatus getParaStatus() {

        return paraStatus;
    }


    public void setParaStatus(ParaStatus value) {
        this.paraStatus = value;
    }


}

Do I need a custom mapper? If so, what?

Thanks!

[Tatu Saloranta]

What would you expect to happen here? Given that `Serializable` does not give any useful indication of expected content type, the only direct improvement could be to consider this same as `List<Object>`, which would result in "untyped" elements (Java String from JSON String, Number from JSON Number etc).

-+ Tatu +-

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[Luke Rahl]

I can get past it using ObjectMapper within a method, but trying to return it via a spring registered message handler doesn't seem to work.It seems to ignore the handler.

[Tatu Saloranta]

One other thing to note is that type of JAXBElement.class is not supported by Jackson, either directly or by JAXB Annotations module -- it is XML-specific construct, and as such is not something that would map well with non-XML content. Not sure if that is relevant here (perhaps that is simply ignored), but thought I'll mention.

-+ Tatu +-