How do I remove empty json nodes in Java with Jackson?

问题:

I'm a beginning java programmer, so I'm sorry if my question is kind of dumb.

I have a JSON object that looks like this:

{ "element1" : {     "generated_name_1": {         "a" : {"isReady":false}     },     "generated_name_2":{},     "generated_name_3":{},     "generated_name_4":{} }, "element2" : {     "generated_name_5" : {         "a" : {"isReady":false},         "g" : {"isReady":false}     } }, "element3" : {      "a" : { "isReady":false},     "n":{} } } 

I would like to go through and delete every element that has an empty value associated with it, like "generated_name_2" and "n". I have no idea what the names of those elements would be, and I have no idea how far nested into the JSON tree it is.

I get that I have to write a recursive program, and this is what I came up with:

public static void cleanJsonNodes(ObjectNode myJsonNode){     for (JsonNode currentNode : myJsonNode){         if (currentNode.size() == 0){             myJsonNode.remove(currentNode);         } else {             cleanJsonNodes((ObjectNode)currentNode);         }     } } 

Of course, this doesn't work, but I'm not really sure where to go from here and I've scoured the internet to no avail.

Please someone help me!

回答1:

I want only to show direction how to do that with Json:

JSONObject jsonObj = new JSONObject(_message);      Map<String, JSONObject> map = jsonObj.getMap();      Iterator<String> it = map.keySet().iterator();      while(it.hasNext()){           String key =   it.next();            JSONObject o = map.get(key);            if(o.length() == 0){               it.remove();           }     } 

When JSONObject loads {} its length is 0, therefore you can drop it.

As A side note, you can use this method in recursion like:

JSONObject jsonObj = new JSONObject(_message);  invoke(jsonObj);  ...  private static void invoke(JSONObject jsonObj) {     Map<String, JSONObject> map = jsonObj.getMap();      Iterator<String> it = map.keySet().iterator();      while(it.hasNext()){         String key =   it.next();          JSONObject o = map.get(key);          if(o.length() == 0){             it.remove();         }         else{             invoke(o);         }     } } 

I didn't add any validation but for sure , you need to verify instance of jsonObj.getMap() ...

回答2:

Check this

How to not send an empty collection in jackson

For empty node in Json you can use

http://jackson.codehaus.org/1.1.2/javadoc/org/codehaus/jackson/node/ObjectNode.html#remove(java.lang.String)

Removing JSON elements with jackson

These can solve your problem.

回答3:

I haven't tested it, but you probably want something like this:

public static void stripEmpty(JsonNode node) {     Iterator<JsonNode> it = node.iterator();     while (it.hasNext()) {         JsonNode child = it.next();         if (child.isObject() && child.isEmpty(null))             it.remove();         else             stripEmpty(child);     } } 

文章来源: How do I remove empty json nodes in Java with Jackson?