Converting Json object to hashmap?

Question

I have a string object representing a json object returning for a network task. I need to convert it into a Map (or HashMap). I've been using gson, but it has been unsuccessful. Here is the json string (please excuse indentation, for I had to manually add newline spaces):

{
"plans":{
"Ankle Recovery":{
"StartDate":"09/24/2018",
"Progress":0.6666666666666666,
"Tasks":[
 {
 "date":"10/16/2018",
 "amount":200,
 "task":"ice ankle for 30 min",
 "completed":true,
 "requirementType":"steps"},
 {
 "date":"10/17/2018",
 "amount":200,
 "task":"ice ankle for 30 min",
 "completed":true,
 "requirementType":"steps"
 },
 {
 "date":"10/18/2018",
 "amount":200,
 "task":"ice ankle for 30 min",
 "completed":false,
 "requirementType":"steps"
 }
],
"Username":"[email protected]",
"Doctor":"Mike Michaels",
"EndDate":"12/24/2018"}},
"status":true
}

This is the code I've been using to make the transformation:

private Map<String, String> plans;
plans = new Gson().fromJson(result, new TypeToken<Map<String, String>>() {}.getType());

Neither nor has worked. I've tried some different solutions across Stack Overflow, but none yield success to this point.

I'm also getting an exception thrown that I don't quite understand:

 com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected a string but was BEGIN_OBJECT at line 1 column 11

(Column 11 is just before the first quote in "AnkleRecovery")

I'd like to use simple gson to make this work if possible. But I'm open to alternative solutions.

• MadProgrammer: Part of the problem is, your JSON is not in the format for Map<String, String>, it has a list of values as well. Personally, I'd devise a POJO which mirrored the structure, but that's me. May try Map<String, Object> instead?
• MadProgrammer: Also, the JSON you've posted is invalid - "Ankle Recovery"{ is wrong - once I correct for that, I can parse it to Map<String, Object>
• Christophe Brown: @MadProgrammer what did you do to correct the JSON?
• MadProgrammer: "Ankle Recovery"{ needs to be "Ankle Recovery": { - one of the first things I always do is put the text through a JSON formatter/validator ;)
• Christophe Brown: @MadProgrammer I see. Another question - when you get your Map, what keys can you see? I only have plans and status. I need the nested values too ("Ankle Recovery" is the one I'm interested in at the moment). How can I have those in a colelcted

Answer 1

The JSON you posted is not valid, line 3:

"Ankle Recovery" : {
// / \
// this is what you are missing

This tool will help you verify the JSON structure and format it as well: https://jsonlint.com/

---

Now to the actual problem. Your JSON has a following structure:

{
 "plans": Object,
 "status": Boolean,
}

Neither of these are strings ( object != string, boolean != string ).
Such a structure can not be mapped to Map<String, String> as this requires the value to be a string.

You will need to create multiple POJOs to define your structure and then map to these, e.g.:

class Project {
 public Map<String,Plan> plans;
 public Boolean status;
}
class Plan {
 public String StartDate;
 public Double Progress;
 public List<Task> tasks;
 ...
}
class Task {
 ...
}

• MadProgrammer: "You will need to create ..." arguably, you don't "have" to, but it would be preferable, assuming the structure is stable, you could just use a Map<String, Object>, but that would take more introspection to decode the results ... just saying ;)
• user9930257: @MadProgrammer correct, technically you don't have to, but such a structure would be useless to anything other than encoding it back to JSON, working with it would be PITA and the code would quickly become a huge mess. So yeah, in real world, you kind of "have" to.
• MadProgrammer: I don't disagree with it been a "mess", but even in the "real" world, some times, it's more pain to have to create a bunch of POJOs just to get to single attribute - but each case needs to be determined on it's own merits. Point in case, the above example uses Ankle Recovery as a key - which is, frankly, an abdominal name for a key - and might signify that the key is not stable
• user9930257: Can't disagree on that. Also, typing all the child objects is not always necessary, e.g. if you will only read the structure to a certain depth. I see that Ankle Recovery is not a stable key as it looks like a plan name, thus the Map<String, Plan> structure, where String is the plan name.

Answer 2

Disclaimer...

I would always investigate using one or more POJOs which can be used to represent the data structure if at all possible.

Without more information, it's impossible to know if keys like Ankle Recovery are stable or not, or if they might change.

"A" possible solution

Generally, JSON is in the form of key/value pairs, where the value might be another JSON object, array or list of other values, so you "could" process the structure directly, for example...

String text = "{\n"
 + " \"plans\":{\n"
 + " \"Ankle Recovery\":{\n"
 + " \"StartDate\":\"09/24/2018\",\n"
 + " \"Progress\":0.6666666666666666,\n"
 + " \"Tasks\":[\n"
 + " {\n"
 + " \"date\":\"10/16/2018\",\n"
 + " \"amount\":200,\n"
 + " \"task\":\"ice ankle for 30 min\",\n"
 + " \"completed\":true,\n"
 + " \"requirementType\":\"steps\"\n"
 + " },\n"
 + " {\n"
 + " \"date\":\"10/17/2018\",\n"
 + " \"amount\":200,\n"
 + " \"task\":\"ice ankle for 30 min\",\n"
 + " \"completed\":true,\n"
 + " \"requirementType\":\"steps\"\n"
 + " },\n"
 + " {\n"
 + " \"date\":\"10/18/2018\",\n"
 + " \"amount\":200,\n"
 + " \"task\":\"ice ankle for 30 min\",\n"
 + " \"completed\":false,\n"
 + " \"requirementType\":\"steps\"\n"
 + " }\n"
 + " ],\n"
 + " \"Username\":\"[email protected]\",\n"
 + " \"Doctor\":\"Mike Michaels\",\n"
 + " \"EndDate\":\"12/24/2018\"\n"
 + " }\n"
 + " },\n"
 + " \"status\":true\n"
 + "}";
Gson gson = new Gson();
Map<String, Object> fromJson = gson.fromJson(text, Map.class);
Map<String, Object> plans = (Map<String, Object>) fromJson.get("plans");
Map<String, Object> recovery = (Map<String, Object>) plans.get("Ankle Recovery");
List<Map<String, Object>> tasks = (List<Map<String, Object>>) recovery.get("Tasks");
for (Map<String, Object> taks : tasks) {
 for (Map.Entry<String, Object> entry : taks.entrySet()) {
 System.out.println(entry.getKey() + " = " + entry.getValue());
 }
}

Now, this would get you the output of ...

date = 10/16/2018
amount = 200.0
task = ice ankle for 30 min
completed = true
requirementType = steps
date = 10/17/2018
amount = 200.0
task = ice ankle for 30 min
completed = true
requirementType = steps
date = 10/18/2018
amount = 200.0
task = ice ankle for 30 min
completed = false
requirementType = steps

Having said all that, your own parsing might be a lot more involved, have to inspect if certain keys exist or not and taking appropriate action as required