How JSONObject method getBoolean("error") works? - java

I have following code which includes error checking expression:
JSONObject obj = new JSONObject(response);
if (!obj.getBoolean("error"))
I am wondering, how getBoolean(String name) works, will it search just "error" string in whole response body & return TRUE or FALSE as we did not provide any arguments except "error" or there is something deeper than this?
Is "error" a key or a value in the returned object?


"error" is a key.
JSONObject represents a single object in JSON, and the JSONObject.getBoolean(String key) method looks for a key-value pair with the given key in that object. It look only at the first level of that one object, not deeper.


error in obj.getBoolean("error") is the key name. getBoolean method looks for error key name and returns its value if it exists and is of Boolean type else throws JSONException. Use optBoolean instead which returns false for exception or fallback value if specified.

Related

How to check whether the 'value' of a 'key' present in the JSONRequest body is empty or not using Java

I have a JSON Request with the body of a request containing three parameters. I need to check whether the 'value' for the 'key' is empty or not in the body of the JSON request. I'm trying this using java code. How can I check this condition in my code?
This is my JSON Request:
{
"Details": [
{
"EmpId" : "123456",
"DeptId" : "12345678",
"Name" : "abc"
}
]
}
Please Note: I have two parameters that have integer values and one that has a String value.

As you have a response in JSONObject jsonObject, you have to check for the key you are looking for, like this :
if(!jsonObject.isNull("EmpId")) {
}
jsonObject.isNull("key") is the method used for checking whether the key is present or not. If the key is not present, this method returns true.
One thing to remember, this method only check whether the key is present in json object or not. If present, you can alternatively check for the value is empty or has some values.
Then check for the value of that particular key like this :
String employeeId = jsonObject.getString("EmpId");.
So you have to traverse like this :
if(!jsonObject.isNull("EmpId")) {
String employeeId = jsonObject.getString("EmpId");
}
Hope it will help you.

How to handle optional keys in JSON response with Java

"app":{
"icon":{
"icon":"TOP_RATED"
},
"message":{
"_type":"TextSpan",
"text":"Top Rated"
}
}
I keep seeing the following code in one of the projects that I have inherited. The JSON response above is parsed as follows
// itemObject has the entire json response
// appObject is a POJO with icon, type fields
String icon= JsonPath.with(itemObject).getAsString("icon/icon");
appObject.setIcon(icon);
String type = "";
try {
type = JsonPath.with(itemObject).getAsString("message/_type");
catch(IllegalArgumentException e) {
// do nothing if type is not found in response
} finally {
// set type to empty string if it's not found
appObject.setType(type);
}
In the scenario, when _type doesn't exist for a specific app, would it be best to surround it with a try/catch block as shown above? It just seems wrong to use try/catch/finally block to process business logic instead of error handling. What is a better way to do the same and can Java 8 Optional help with this?

I find the org.json package simple and straightforward. It is found here. The org.json.JSONObject class, for example, contains the public boolean has(String key) method, which is used to check if a certain key exists.
Returns true if this object has a mapping for name. The mapping may be NULL.
You can check this way where 'HAS' - Returns true if this object has a mapping for name. The mapping may be NULL.
if (json.has("status")) {
String status = json.getString("status"));
}
if (json.has("club")) {
String club = json.getString("club"));
}
You can also check using 'isNull' - Returns true if this object has no
mapping for name or if it has a mapping whose value is NULL.
if (!json.isNull("club"))
String club = json.getString("club"));
http://developer.android.com/reference/org/json/JSONObject.html#has(java.lang.String)

Why JsonNull in GSON?

The docs say the JsonObject#get method returns null if no such member exists. That's not accurate; sometimes a JsonNull object is returned instead of null.
What is the idiom for checking whether a particular field exists in GSON? I wish to avoid this clunky style:
jsonElement = jsonObject.get("optional_field");
if (jsonElement != null && !jsonElement.isJsonNull()) {
s = jsonElement .getAsString();
}
Why did GSON use JsonNull instead of null?
There is an answer for what are the differences between null and JsonNull. In my question above, I'm looking for the reasons why.

Gson, presumably, wanted to model the difference between the absence of a value and the presence of the JSON value null in the JSON. For example, there's a difference between these two JSON snippets
{}
{"key":null}
your application might consider them the same, but the JSON format doesn't.
Calling
JsonObject jsonObject = new JsonObject(); // {}
jsonObject.get("key");
returns the Java value null because no member exists with that name.
Calling
JsonObject jsonObject = new JsonObject();
jsonObject.add("key", JsonNull.INSTANCE /* or even null */); // {"key":null}
jsonObject.get("key");
returns an instance of type JsonNull (the singleton referenced by JsonNull.INSTANCE) because a member does exist with that name and its value is JSON null, represented by the JsonNull value.

I know question is not asking for a solution, but I came here looking for one. So I will post it in case someone else needs it.
Below Kotlin extension code saves the trouble of checking for null and isJsonNull separately for each element
import com.google.gson.JsonElement
import com.google.gson.JsonObject
fun JsonObject.getNullable(key: String): JsonElement? {
val value: JsonElement = this.get(key) ?: return null
if (value.isJsonNull) {
return null
}
return value
}
and instead of calling like this
jsonObject.get("name")
you call like this
jsonObject.getNullable("name")
Works particularly great in nested structures. Your code eventually would look like this
val name = jsonObject.getNullable("owner")?.asJsonObject?.
getNullable("personDetails")?.asJsonObject?.
getNullable("name")
?: ""

How to check if a JSON key exists?

So, I get some JSON values from the server but I don't know if there will be a particular field or not.
So like:
{ "regatta_name":"ProbaRegatta",
"country":"Congo",
"status":"invited"
}
And sometimes, there will be an extra field like:
{ "regatta_name":"ProbaRegatta",
"country":"Congo",
"status":"invited",
"club":"somevalue"
}
I would like to check if the field named "club" exists so that at parsing I won't get
org.json.JSONException: No value for club

JSONObject class has a method named "has":
http://developer.android.com/reference/org/json/JSONObject.html#has(java.lang.String)
Returns true if this object has a mapping for name. The mapping may be NULL.

You can check this way where 'HAS' - Returns true if this object has a mapping for name. The mapping may be NULL.
if (json.has("status")) {
String status = json.getString("status"));
}
if (json.has("club")) {
String club = json.getString("club"));
}
You can also check using 'isNull' - Returns true if this object has no
mapping for name or if it has a mapping whose value is NULL.
if (!json.isNull("club"))
String club = json.getString("club"));

you could JSONObject#has, providing the key as input and check if the method returns true or false. You could also
use optString instead of getString:
Returns the value mapped by name if it exists, coercing it if
necessary. Returns the empty string if no such mapping exists

just before read key check it like before read
JSONObject json_obj=new JSONObject(yourjsonstr);
if(!json_obj.isNull("club"))
{
//it's contain value to be read operation
}
else
{
//it's not contain key club or isnull so do this operation here
}
isNull function definition
Returns true if this object has no mapping for name or
if it has a mapping whose value is NULL.
official documentation below link for isNull function
http://developer.android.com/reference/org/json/JSONObject.html#isNull(java.lang.String)

You can use has
public boolean has(String key)
Determine if the JSONObject contains a specific key.
Example
JSONObject JsonObj = new JSONObject(Your_API_STRING); //JSONObject is an unordered collection of name/value pairs
if (JsonObj.has("address")) {
//Checking address Key Present or not
String get_address = JsonObj .getString("address"); // Present Key
}
else {
//Do Your Staff
}

A better way, instead of using a conditional like:
if (json.has("club")) {
String club = json.getString("club"));
}
is to simply use the existing method optString(), like this:
String club = json.optString("club);
the optString("key") method will return an empty String if the key does not exist and won't, therefore, throw you an exception.

Try this:
let json=yourJson
if(json.hasOwnProperty(yourKey)){
value=json[yourKey]
}

Json has a method called containsKey().
You can use it to check if a certain key is contained in the Json set.
File jsonInputFile = new File("jsonFile.json");
InputStream is = new FileInputStream(jsonInputFile);
JsonReader reader = Json.createReader(is);
JsonObject frameObj = reader.readObject();
reader.close();
if frameObj.containsKey("person") {
//Do stuff
}

Try this
if(!jsonObj.isNull("club")){
jsonObj.getString("club");
}

I used hasOwnProperty('club')
var myobj = { "regatta_name":"ProbaRegatta",
"country":"Congo",
"status":"invited"
};
if ( myobj.hasOwnProperty("club"))
// do something with club (will be false with above data)
var data = myobj.club;
if ( myobj.hasOwnProperty("status"))
// do something with the status field. (will be true with above ..)
var data = myobj.status;
works in all current browsers.

You can try this to check wether the key exists or not:
JSONObject object = new JSONObject(jsonfile);
if (object.containskey("key")) {
object.get("key");
//etc. etc.
}

I am just adding another thing, In case you just want to check whether anything is created in JSONObject or not you can use length(), because by default when JSONObject is initialized and no key is inserted, it just has empty braces {} and using has(String key) doesn't make any sense.
So you can directly write if (jsonObject.length() > 0) and do your things.
Happy learning!

You can use the JsonNode#hasNonNull(String fieldName), it mix the has method and the verification if it is a null value or not

Setting a default value for empty json field

I have to parse a json whom a field can be empty:
{"fullField":"ok","canBeEmpty":""}
if I try to parse this string overall parsing fails with a "no value for canBeEmpty".
For each json item I execute:
json_data.getString("field"); //throws exception if empty
I'd like to still keep the parsing, setting the canBeEmpty value to a default string...is it possibile?

you can use JSONObject.JSONObject(String name) to check if any name is exist or not in json object as:
if(JSONObject.isNull("field")){
// do something here
}
else{
//do something here
}

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