JSONObject not found

Programming Questions

AlexB

in Programming Questions • 2 months ago

I'm having some trouble with JSON and Java, I have a working function to export a data strucutre into JSON and save it in a file. But when I try to do the reverse and import the data strucutre back into java, I get an error, the output of which is:

java.lang.reflect.InvocationTargetException at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at ..... Caused by: java.lang.RuntimeException: JSONObject["nodeID"] not found. at processing.data.JSONObject.get(JSONObject.java:549) at processing.data.JSONObject.getString(JSONObject.java:568) at Graph.loadJSON(Graph.java:934) ... 21 more

From that error I take that the String 'nodeID' can't be found within the node, but it is in the JSON output, which looks like this:

{"network": [ {"node": { "nodeID": "1", "radius": 40 "atom": { "id": "a-2675-EH", "activeTime": 0, "type": "Motor", "linkFrom": [{ "atomID": "a-2312-TL", "delay": 0.20000000298023224 }], "linkTo": [{ "atomID": "a-3289-Ql", "delay": 0.20000000298023224 }] }, .....

The JSON code is an array of nodes contained within network, then each node object contains a String nodeID, and 3 Float variables, then an Object called atom. This atom then contains two Strings, a float, and 2 arrays called linkTo and linkFrom, which contain objects to represent a link (atomID and delay, string and float respectfully)

And the Java code to load each node from the network looks like this:

JSONObject network = loadJSONObject(selection.getAbsolutePath()); JSONArray nodes = network.getJSONArray("network"); for (int i=0; i<nodes.size(); i++) { //Load node JSONObject node = nodes.getJSONObject(i); String nodeID = node.getString("nodeID"); <-- Error occurs here Float x = node.getFloat("x"); Float y = node.getFloat("y"); Float radius = node.getFloat("radius"); JSONObject atom = node.getJSONObject("atom"); .....

I'm sure I'm just missing something simple, but I've spent nearly a week trying to tweak this and getting nowhere!

I know the node is loading properly, because a println(node) statement inside the for loop prints out the node exactly as it should, it's just trying to fetch the nodeID that seems to not work. Even if I change the order and try to fetch the x, or y float that causes the error too.

Thanks.

Replies(2)

PhiLho

Re: JSONObject not found

2 months ago

Your code in one line is hard to read... You should try and paste it differently, so we can read it.
But don't forget the Json data is structured. Usually, either you specify a path when getting an information (like "network/node/nodeId", I think) or you have to read each sub-node to reach the one you are interested in.

AlexB

Re: Re: JSONObject not found

2 months ago

Yeah, I'm not sure why it did that, I paste in the question from StackOverflow, and it appeared fine in the preview view. Then when I published the question it came out like that!

Someone found a solution on StackOverflow, http://stackoverflow.com/questions/17808618/java-json-object-not-found - basically there was an extra curly bracket before the node, so the structure is more like network - node - node - nodeID, which is confusing, but just saying node.getJSONObject("node").getString("nodeID") did the trick.

Top Reply