Question

I am working on how to serialised a POJO into a json string. I am using the jackson library and have run into a problem.

A value in the json object can either be a string or a string array like so…

{"mimeTypes":"all"}

or

 {"mimeTypes":["application/pdf", "application/msword"]}

This is my approach at the moment

@JsonIgnore
private String mimeTypes;
@JsonIgnore
private String[] mimeTypesArray;
@JsonRawValue
@JsonProperty("integration/enabled-mime-types")
private String mimeType;

public void setMimeTypes(String mimeTypes) {
    this.mimeTypes = mimeTypes;
    mimeType = mimeTypes;
}

public void setMimeTypes(String[] mimeTypes) {
    this.mimeTypesArray = mimeTypes;
    try {
        JSONArray jsonArray = new JSONArray(mimeTypes);
        this.mimeType = jsonArray.toString();
    } catch (JSONException e) {
        e.printStackTrace();  //To change body of catch statement use File | Settings | File Templates.
    }
}

Basically I have a field for the string, a field for the string array, and a field for the string I want to add to the json object. I serialise on the setter so the object mapper doesn’t have to choose which field to use.

This feels like a hacky way of doing things. Would there be a better solution? I have been reading about using jackson views but I am not sure if this is possible for my problem.

Answer 1

I haven’t tested it, but I’d try adding a dedicated method for computing what should be serialized:

class MyMimeTypes {
    @JsonIgnore
    private String[] mimeTypesArray;

    /** A convenience method for setting just one item. */
    public void setMimeType(String mimeType) {
        this.mimeTypesArray = new String[] { mimeType };
    }

    public void setMimeTypes(String[] mimeTypes) {
        this.mimeTypesArray = mimeTypes;
    }

    // The JSON-specific part:

    @JsonProperty("mimeTypes")
    public Object jsonMimeTypes() {
        if (mimeTypesArray.length == 1)
            return mimeTypesArray[0];
        else
            return mimeTypesArray;
    }
}

This way, if you have just one item in the array, the serialized value will be just the item. Otherwise the whole array will be serialized.

Note that it is a bad practise having two setters with the same name and different signatures. AFAIK that violates the Java Beans specification.

Perhaps you could use a vararg method here to replace the two setters (but I don’t know how this goes together with Java Beans specification):

public void setMimeTypes(String... mimeTypes) {
    this.mimeTypesArray = mimeTypes;
}