Parse JSON tree to plain class using Jackson or its alternatives

Question

How to parse that JSON:

{
    \"foo\": {
        \"bar\": {
            \"baz\": \"Hello\"
        },
        \"qux\": \"World\"
    }
}

Into t

Answer 1

Note: I'm the EclipseLink JAXB (MOXy) lead and a member of the JAXB (JSR-222) expert group.

This use case may not be possible with Jackson, but can be done when MOXy is used as your JSON-binding provider.

Foo

You can take advantage of MOXy's path based mapping for this use case.

import org.eclipse.persistence.oxm.annotations.XmlPath;

public class Foo {

    private String baz;
    private String qux;

    @XmlPath("foo/bar/baz/text()")
    public String getBaz() {
        return baz;
    }

    public void setBaz(final String baz) {
        this.baz = baz;
    }

    @XmlPath("foo/qux/text()")
    public String getQux() {
        return qux;
    }

    public void setQux(final String qux) {
        this.qux = qux;
    }

}

Demo

The JAXB runtime APIs are used to read/write the JSON.

import java.util.*;
import javax.xml.bind.*;
import javax.xml.transform.stream.StreamSource;
import org.eclipse.persistence.jaxb.JAXBContextProperties;

public class Demo {

    public static void main(String[] args) throws Exception {
        Map<String, Object> properties = new HashMap<String, Object>(2);
        properties.put(JAXBContextProperties.MEDIA_TYPE, "application/json");
        properties.put(JAXBContextProperties.JSON_INCLUDE_ROOT, false);
        JAXBContext jc = JAXBContext.newInstance(new Class[] {Foo.class}, properties);

        Unmarshaller unmarshaller = jc.createUnmarshaller();
        StreamSource json = new StreamSource("src/forum15659950/input.json");
        Foo foo = unmarshaller.unmarshal(json, Foo.class).getValue();

        Marshaller marshaller = jc.createMarshaller();
        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
        marshaller.marshal(foo, System.out);
    }

}

input.json/Output

{
   "foo" : {
      "bar" : {
         "baz" : "Hello"
      },
      "qux" : "World"
   }
}

For More Information

• http://blog.bdoughan.com/2011/05/specifying-eclipselink-moxy-as-your.html
• http://blog.bdoughan.com/2011/08/json-binding-with-eclipselink-moxy.html

Answer 2

I have found, that this feature is not implemented in Jackson yet, see issue.

As a workaround, method below can be added into Foo class:

@JsonProperty("foo")
public void setFoo(JsonNode jsonNode) {
    this.qux = jsonNode.get("qux").getTextValue();
    this.baz = jsonNode.get("bar").get("baz").getTextValue();
}