Flattening a 3 level nested JSON string in java

Question

The requirement is to create a generic flattening utility for an input JSON object to a flattened JSON object.

The sample JSON looks like the below

Answer 1

Try this code:

public static void flattenJson(JsonNode node, String parent, Map map) {
    if (node instanceof ValueNode) {
        map.put(parent, (ValueNode)node);
    } else {
        String prefix = parent == null ? "" : parent + ".";
        if (node instanceof ArrayNode) {
            ArrayNode arrayNode = (ArrayNode)node;
            for(int i = 0; i < arrayNode.size(); i++) {
                flattenJson(arrayNode.get(i), prefix + i, map);
            }
        } else if (node instanceof ObjectNode) {
            ObjectNode objectNode = (ObjectNode) node;
            for (Iterator> it = objectNode.fields(); it.hasNext(); ) {
                Map.Entry field = it.next();
                flattenJson(field.getValue(), prefix + field.getKey(), map);
            }
        } else {
            throw new RuntimeException("unknown json node");
        }
    }
}

public static Map flattenJson(JsonNode input) {
    Map map = new LinkedHashMap<>();
    flattenJson(input, null, map);
    return map;
}

Then you can call

    ObjectMapper om = new ObjectMapper();
    JsonNode jsonNode = om.readTree(json);
    Map m = flattenJson(jsonNode);
    for (Map.Entry kv : m.entrySet()) {
        System.out.println(kv.getKey() + "=" + kv.getValue().asText());
    }

Output:

Source=source-1
Rows.0.Keys.device-id=BC04-EBH-N3K-01
Rows.0.Keys.interface-name=TenGigE0/0/0/39
Rows.0.Keys.node-name=0/0/CPU0
Rows.0.Timestamp=1567621527656
Rows.0.inner.donm.id=0062
Rows.0.inner.donm.mol.rem=30
Rows.0.inner.donm.mol.len=11
Rows.0.inner.donm.mol.org.ldp.0.t=486
Rows.0.inner.donm.mol.org.ldp.0.o=322
Rows.0.inner.donm.mol.org.ldp.1.t=487
Rows.0.inner.donm.mol.org.ldp.1.o=32
Rows.0.inner.donm.mol.org.ldp.1.twss=1
Rows.0.inner.donm.mol.org.ldp.1.tlv=00:01
Rows.0.inner.donm.mol.chlen=14
Rows.0.inner.donm.mol.poe=5
Rows.0.inner.donm.mol.combs=10
Rows.0.inner.donm.mol.chaype=4
Rows.0.inner.donm.mol.rek=0
Rows.0.inner.donm.mol.rem-um=67
Rows.0.inner.donm.detail.enas=B,R
Rows.0.inner.donm.detail.systes=B,R
Rows.0.inner.donm.detail.timng=91
Rows.0.inner.donm.detail.syn=C
Rows.0.inner.donm.detail.met-type=0
Rows.0.inner.donm.detail.neses.lldEDIT.0.ium=830
Rows.0.inner.donm.detail.neses.lldEDIT.0.m=1
Rows.0.inner.donm.detail.neses.lldEDIT.0.ass.ape=ipv4
Rows.0.inner.donm.detail.neses.lldEDIT.0.ass.ipvs=94
Rows.0.inner.donm.detail.pess=0008
Rows.0.inner.donm.detail.por]d=0
Rows.0.inner.donm.detail.pon=BCtive
Rows.0.inner.donm.detail.sysme=BC1
Rows.0.inner.donm.reme=Bu1
Rows.0.inner.donm.hean=0
Rows.0.inner.donm.porl=Et1
Tey.epath=Cgetail
Tey.sustr=MX
Tey.coime=1567621527653
Tey.msp=1567621527653
Tey.come=1567621527660
Tey.nor=BC5
Tey.cid=14789654