Converting xml string to 'this' class using jackson

Question

I am using Jackson to work with my XML data, based on this Baeldung tutorial.

I have the following class to model some XML:

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.dataformat.xml.XmlMapper;

public class SimpleBean {

    private int x = 1;
    private int y = 2;

    public int getX() {
        return x;
    }

    public void setX(int x) {
        this.x = x;
    }

    public int getY() {
        return y;
    }

    public void setY(int y) {
        this.y = y;
    }

    public SimpleBean fromString(String xml) throws JsonProcessingException {
        XmlMapper xmlMapper = new XmlMapper();
        return xmlMapper.readValue(xml, SimpleBean.class);
    }
}

I have the following test that passes:

@Test
void testFromString() throws Exception {
    SimpleBean bean = new SimpleBean();
    String xml = "<SimpleBean><x>11</x><y>22</y></SimpleBean>";
    SimpleBean beanParsed = bean.fromString(xml);
    Assertions.assertEquals(11, beanParsed.getX());
}

What I would like to do is something like this:

@Test
void testFromStringWanted() throws Exception {
    SimpleBean bean = new SimpleBean();
    String xml = "<SimpleBean><x>11</x><y>22</y></SimpleBean>";
    bean.fromString(xml);
    Assertions.assertEquals(11, bean.getX());  // FAILS
}

I would like to parse the string into the instance bean that I already have. I do not want to have to create a second beanParsed.

I tried to change my fromString method to:

public void fromString(String xml) throws JsonProcessingException {
    XmlMapper xmlMapper = new XmlMapper();
    xmlMapper.readValue(xml, this.getClass());
}

but that did not work. No errors, it just did not produce the desired results.

Also tried this, but that does not even compile!

public void fromString(String xml) throws JsonProcessingException {
    XmlMapper xmlMapper = new XmlMapper();
    this = xmlMapper.readValue(xml, SimpleBean.class);
}

How can I do this?

Answer 1

Try:

public void fromString(String xml) throws JsonProcessingException {
    XmlMapper xmlMapper = new XmlMapper();
    // Use readerForUpdating() to parse into the existing instance
    xmlMapper.readerForUpdating(this).readValue(xml);
}

Jackson provides a method called readerForUpdating() specifically for parsing data into an existing object.

This method creates a reader that updates an existing object instead of creating a new one.