马歇尔/解马歇尔地图

Question

@XmlRootElement @XmlAccessorType(XmlAccessType.FIELD) public class ItemSubstitutionRequestDTO { public ItemSubstitutionRequestDTO() { } private List<Map<String,Integer>> substituteFor=new ArrayList<Map<String,Integer>>(); private String orderId; public List<Map<String,Integer>> getSubstituteFor() { return substituteFor; } public void setSubstituteFor(List<Map<String,Integer>> substituteFor) { this.substituteFor = substituteFor; } public String getOrderId() { return orderId; } public void setOrderId(String orderId) { this.orderId = orderId; } }

Final result ERROR :

java.util.Map is an interface, and JAXB can't handle interfaces.

I can't get JaxB to be able to marshall/unmarshall instances of Map.I tried other annotation also and found this is one of the possible way to solve the above error but nothing is woking.

Below is the input json which is coming from UI side

{ "itemSubstitutionRequestDTO": { "substituteFor": [{"41712":2}], "orderId": "1073901", } }

Answer 1

You didn't write how your XML content within the <substituteFor> element would look like. Therefore I assume something like this:

<itemSubstitutionRequestDTO>
    <substituteFor>
        <item>
            <key>x</key>
            <value>23</value>
        </item>
        <item>
            <key>y</key>
            <value>3</value>
        </item>
    </substituteFor>
    <orderId>abc</orderId>
</itemSubstitutionRequestDTO>

As the JAXB error message already told you, it can't handle types with an interface between the < > , like for example your List<Map<String,Integer>> . However it can handle types with a normal class between < > , like List<SubstitutionMap> .

So the first step is to rewrite your ItemSubstitutionRequestDTO class so that it does not use List<Map<String,Integer>> , but instead List<SubstitutionMap> . You need to write the SubstitutionMap class (not an interface) by yourself. But it can be extremely simple:

public class SubstitutionMap extends HashMap<String, Integer> {
}

Now JAXB doesn't throw an error anymore, but it still doesn't know how to marshal/unmarshal a SubstitutionMap . Therefore you need to write an XmlAdapter for it. Let's call it SubstitutionMapAdapter . To make JAXB aware of this adapter, you need to annotate the substituteFor property in your ItemSubstitutionRequestDTO class with:

@XmlJavaTypeAdapter(SubstitutionMapAdapter.class)

The adapter's job is to do the actual conversion from SubstitutionMap to an array of SubstitutionMapElement s and vice versa. Then JAXB can handle the SubstitutionMapElement array by itself.

public class SubstitutionMapAdapter extends XmlAdapter<SubstitutionMapElement[], SubstitutionMap> {

    @Override
    public SubstitutionMap unmarshal(SubstitutionMapElement[] elements) {
        if (elements == null)
            return null;
        SubstitutionMap map = new SubstitutionMap();
        for (SubstitutionMapElement element : elements)
            map.put(element.getKey(), element.getValue());
        return map;
    }

    @Override
    public SubstitutionMapElement[] marshal(SubstitutionMap map) {
        // ... (left to you as exercise)
    }
}

The class SubstitutionMapElement is just a simple container for a key and a value.

@XmlAccessorType(XmlAccessType.FIELD)
public class SubstitutionMapElement {

    private String key;
    private int value;
    
    // ... constructors, getters, setters omitted here for brevity
}