Extracting associated JSON data using the unique key

Question

I'm new to Java and have used the long piece of code provided in

GWT: Dealing with incoming JSON string

to read the json similar to the layout of the original posting person raised.

My layout is as follows:

{
    "messagedata": [
        {
            "msgkey": "12552",
            "reference": "201708010001",
            "bic": "PARABLULLEISI",
            "securityid": "BE0003735496",
            "safekeepingacc": "7744085P"
        },
        {
            "msgkey": "12553",
            "reference": "000081676368",
            "bic": "PARABLULLEISX",
            "securityid": "CNE00000BQ0",
            "safekeepingacc": "1053542760H"
        }

    ]
}

But the final line of code (jsonString.stringValue()) only ever reads the first block of JSON data i.e. msgkey or bic from the first section.

How would i get data from other sections i.e. if there were 3 sections each containing msgkey, bic, reference etc

More importantly if i know the msgkey value as in the sample JSON how can I get the other associated values for that section when the msgkey value changes?

I've used the library com.google.gwt.json.client.*

Thanks Martin

Answer 1

You can use JsInterop and JSON.parse in GWT 2.8 + elemental2.

import com.google.gwt.core.client.EntryPoint;
import elemental2.core.Global;
import elemental2.dom.DomGlobal;
import java.util.stream.Stream;
import jsinterop.annotations.*;
import jsinterop.base.Js;

class JsInteropExample implements EntryPoint {
    @JsType(isNative = true, namespace = JsPackage.GLOBAL, name = "Object")
    static class Message {
        public Data[] messagedata;
    }

    @JsType(isNative = true, namespace = JsPackage.GLOBAL, name = "Object")
    static class Data {
        public String msgkey;
        public String reference;
        public String bic;
        public String securityid;
        public String safekeepingacc;
    }

    @Override public void onModuleLoad() {
        Message msg = Js.cast(Global.JSON.parse("{\"messagedata\": […]}"));
        Stream.of(msg.messagedata).forEach(d -> DomGlobal.console.log(d.msgkey));
    }
}

Answer 2

I totally agree with Ignacio, JsInterop is the way, that is why I was asking about GWT version.

JsInterop will automatically map getter and setter to the right property as you can see below.

It also allow you to add java overlay methods to your native objects, which I personally find very convenient and clean.

In order to have this code working you need to make sure to have elemental2 and jsinterop imported in your gwt.xml files.

import com.google.gwt.core.client.EntryPoint;
import elemental2.core.Global;
import elemental2.dom.DomGlobal;
import java.util.stream.Stream;
import jsinterop.annotations.*;
import jsinterop.base.Js;

class JsInteropExample implements EntryPoint {
    @JsType(isNative = true, namespace = JsPackage.GLOBAL, name = "Object")
    static abstract class Message {

        @JsProperty
        public abstract Data[] getMessagedata();

        @JsOverlay
        public void logObject(){
            Stream.of(getMessagedata).forEach(d -> DomGlobal.console.log(d.msgkey));
        }
    }

    @JsType(isNative = true, namespace = JsPackage.GLOBAL, name = "Object")
    static class Data {
        public String msgkey;
        public String reference;
        public String bic;
        public String securityid;
        public String safekeepingacc;
    }

    @Override public void onModuleLoad() {
        Message msg = Js.cast(Global.JSON.parse("{\"messagedata\": […]}"));
        Stream.of(msg.messagedata).forEach(d -> DomGlobal.console.log(d.msgkey));
    }
}

If you want to avoid using elemental2 you can decode the Json by using:

@JsMethod(namespace="JSON")
static native DivData parse(String json);