Develop Reference

get a key value pair from a String json (simple object)

Im trying to get a key:value pair from a simple jsonString to add it after into a memory tab. If facing an issue cause my input is a string. and it looks like my loop isnot able to read the key value pair.
I read many topics about it, and im still in trouble with it. As you can see below
{"nom":"BRUN","prenom":"Albert","date_naiss":"10-10-1960","adr_email":"abrun#gmail.com","titre":"Mr","sexe":"F"}
and my method, find only on object... the result is the same in my loop
public static ArrayHandler jsonSimpleObjectToTab(String data) throws ParseException {
if( data instanceof String) {
final var jsonParser = new JSONParser();
final var object = jsonParser.parse(data);
final var array = new JSONArray();
array.put(object);
final var handler = new ArrayHandler("BW_funct_Struct");
for( KeyValuePair element : array) {
handler.addCell(element);
Log.warn(handler);
}
return handler;
} else {
throw new IllegalArgumentException("jsonSimpleObjectToTab: do not support complex object" + data + "to Tab");
}
}
i also tryed before to type my array as a List, Object etc, without the keyValuePair object, i would appreciate some help.
Thanks again dear StackOverFlowers ;)

You can try this :
const json = '{"nom":"BRUN","prenom":"Albert","date_naiss":"10-10-1960","adr_email":"abrun#gmail.com","titre":"Mr","sexe":"F"}';
map = new Map();
const obj = JSON.parse(json,(key,value) => {
map.set(key,value)
});
and you'll have every pair stored in map

Simply split the whole line at the commas and then split the resulting parts at the colon. This should give you the individual parts for your names and values.
Try:
supposing
String input = "\"nom\":\"BRUN\",\"prenom\":\"Albert\"";
then
String[] nameValuePairs = input.split(",");
for(String pair : nameValuePairs)
{
String[] nameValue = pair.split(":");
String name = nameValue[0]; // use it as you need it ...
String value = nameValue[1]; // use it as you need it ...
}

You can use TypeReference to convert to Map<String,String> so that you have key value pair.
String json = "{\"nom\":\"BRUN\",\"prenom\":\"Albert\",\"date_naiss\":\"10-10-1960\",\"adr_email\":\"abrun#gmail.com\",\"titre\":\"Mr\",\"sexe\":\"F\"}";
ObjectMapper objectMapper = new ObjectMapper();
TypeReference<Map<String,String>> typeReference = new TypeReference<Map<String, String>>() {
};
Map<String,String> map = objectMapper.readValue(json, typeReference);

I just answered a very similar question. The gist of it is that you need to parse your Json String into some Object. In your case you can parse it to Map. Here is the link to the question with my answer. But here is a short version: you can use any Json library but the recommended ones would be Jackson Json (also known as faster XML) or Gson(by Google) Here is their user guide site. To parse your Json text to a class instance you can use ObjectMapper class which is part of Jackson-Json library. For example
public <T> T readValue(String content,
TypeReference valueTypeRef)
throws IOException,
JsonParseException,
JsonMappingException
See Javadoc. But also I may suggest a very simple JsonUtils class which is a thin wrapper over ObjectMapper class. Your code could be as simple as this:
Map<String, Object> map;
try {
map = JsonUtils.readObjectFromJsonString(input , Map.class);
} catch(IOException ioe) {
....
}
Here is a Javadoc for JsonUtils class. This class is a part of MgntUtils open source library written and maintained by me. You can get it as Maven artifacts or from the Github

Java | GSON | Add JSON objects to excisting JSON-File

I have currently started a kind of diary project to teach myself how to code, which I write in Java. The project has a graphical interface which I realized with JavaFX.
I want to write data into a JSON file, which I enter into two text fields and a slider. Such a JSON entry should look like this:
{
"2019-01-13": {
"textfield1": "test1",
"textfield2": "test2",
"Slider": 2
}
}
I have already created a class in which the values can be passed and retrieved by the JSONWriter.
The class looks like this:
public class Entry {
private String date, textfield1, textfield2;
private Integer slider;
public String getDate() {
return date;
}
public void setDate(String date) {
this.date = date;
}
public String getTextfield1() {
return textfield1;
}
public void setTextfield1(String textfield1) {
this.textfield1 = textfield1;
}
public String getTextfield2() {
return textfield2;
}
public void setTextfield2(String textfield2) {
this.textfield2 = textfield2;
}
public Integer getSlider() {
return slider;
}
public void setSlider(Integer slider) {
this.slider= slider;
}
}
The code of the JSONWriter looks like this:
void json() throws IOException {
Gson gson = new GsonBuilder().setPrettyPrinting().create();
JsonWriter writer = new JsonWriter(new FileWriter("test.json",true));
JsonParser parser = new JsonParser();
Object obj = parser.parse(new FileReader("test.json"));
JsonObject jsonObject = (JsonObject) obj;
System.out.println(jsonObject);
writer.beginObject();
writer.name(entry.getDate());
writer.beginObject();
writer.name("textfield1").value(entry.getTextfield1());
writer.name("textfield2").value(entry.getTextfield2());
writer.name("Slider").value(entry.getSlider());
writer.endObject();
writer.endObject();
writer.close();
}
The date is obtained from the datepicker. Later I want to filter the data from the Json file by date and transfer the containing objects (textfield 1, textfiel2, slider) into the corresponding fields.
If possible, I would also like to try to overwrite the objects of a date. This means, if an entry of the date already exists and I want to change something in the entries, it should be replaced in the JSON file, so I can retrieve it later.
If you can recommend a better memory type for this kind of application, I am open for it. But it should also be compatible with databases later on. Later I would like to deal with databases as well.
So far I have no idea how to do this because I am still at the beginning of programming. I've been looking for posts that could cover the topic, but I haven't really found anything I understand.

You could start without JsonParser and JsonWriter and use Gson's fromJson(..) and toJson(..) because your current Json format is easily mapped as a map of entry POJOs.
Creating some complex implementation with JsonParser & JsonWriter might be more efficient for big amounts of data but in that point you already should have studied how to persist to db anyway.
POJOs are easy to manipulate and they can be later easily persisted to db - for example if you decide to use technology like JPA with only few annotations.
See below simple example:
#Test
public void test() throws IOException {
Gson gson = new GsonBuilder().setPrettyPrinting().create();
// Your current Json seems to be a map with date string as a key
// Create a corresponding type for gson to deserialize to
// correct generic types
Type type = new TypeToken<Map<String, Entry>>() {}.getType();
// Check this file name for your environment
String fileName = "src/test/java/org/example/diary/test.json";
Reader reader = new FileReader(new File(fileName));
// Read the whole diary to memory as java objects
Map<String, Entry> diary = gson.fromJson(reader, type);
// Modify one field
diary.get("2019-01-13").setTextfield1("modified field");
// Add a new date entry
Entry e = new Entry();
e.setDate("2019-01-14");
e.setScale(3);
e.setTextfield1("Dear Diary");
e.setTextfield1("I met a ...");
diary.put(e.getDate(), e);
// Store the new diary contents. Note that this one does not overwrite the
// original file but appends ".out.json" to file name to preserver the original
FileWriter fw = new FileWriter(new File(fileName + ".out.json"));
gson.toJson(diary, fw);
fw.close();
}
This should result test.json.out.json like:
{
"2019-01-13": {
"textfield1": "modified field",
"textfield2": "test2",
"Slider": 2
},
"2019-01-14": {
"date": "2019-01-14",
"textfield1": "Dear Diary",
"textfield2": "I met a ...",
"Slider": 3
}
}
Note that I also made little assumption about this:
// Just in case you meant to map "Slider" in Json as "scale"
#SerializedName("Slider")
private Integer scale;

I will give you general tips up to you to go deeper.
First of all, I recommend you this architecture that is common on web-applications or even desktop apps to get the front-end layer separately of back-end server:
Front-end (use Java Fx if you want). Tutorial: http://www.mastertheboss.com/jboss-frameworks/resteasy/rest-services-using-javafx-tutorial
Back-end (Java 1.8, Springboot, MySQL database). Example: there are tons of examples and tutorials using this stack, I recommend mykong or baeldung blogs.
The front-end will communicate to server over HTTP request through back-end REST API using JSON or XML format for messaging. In real life there are physically separated but just create 2 different java projects running on different ports.
For the back-end, just follow the tutorial to get up and running a REST API server. Set up MVC pattern: Controller layer, Service layer, Repository layer, model layer, dto layers, etc. For your specific model I recommend you the following:
selected_date: Date
inputs: Map of strings
size: Integer
On Front-end project with Java FX, just re-use the code you already wrote and add some CSS if you want. Use the components actions to call the back-end REST API to create, retrieve, update and delete your data from date-picker or whatever operation you want to do.
You will transform java objects into JSON strings permanently, I recommend you to use Gson library or Jackson library that do this in a direct way and it is not need to build the JsonObject manually. If you still want to write the JSON into a file, transform the java object into string (this is a string with the object written in JSON format) using the mentioned libraries, and then write the string into file. But I strongly believe it will more practice if you implement database.
Hope it helps

Supercsv - unable to find method exception

I have the below implementation.
csvReader = new CsvBeanReader(new InputStreamReader(stream), CsvPreference.STANDARD_PREFERENCE);
lastReadIdentity = (T) csvReader.read(Packages.class, Packages.COLS);
In my Packages.class
I have set my unitcount variable.
public String getUnitCount() {
return unitCount;
}
public void setUnitCount(String unitCount) {
this.unitCount = unitCount;
}
This works fine when it is taken as a string, but when taken as a integer, it throws the below exception. Please help
private int unitCount;
public int getUnitCount() {
return unitCount;
}
public void setUnitCount(int unitCount) {
this.unitCount = unitCount;
}
Exception:
org.supercsv.exception.SuperCsvReflectionException: unable to find method setUnitCount(java.lang.String) in class com.directv.sms.data.SubscriberPackages - check that the corresponding nameMapping element matches the field name in the bean, and the cell processor returns a type compatible with the field
context=null
at org.supercsv.util.ReflectionUtils.findSetter(ReflectionUtils.java:139)
at org.supercsv.util.MethodCache.getSetMethod(MethodCache.java:95)

I'm not sure about SuperCsv, but univocity-parsers should be able to handle this without a hitch, not to mention it is at least 3 times faster to parse your input.
Just annotate your class:
public class SubscriberPackages {
#Parsed(defaultNullRead = "0") // if the file contains nulls, then they will be converted to 0.
private int unitCount; // The attribute name will be matched against the column header in the file automatically.
}
To parse the CSV into beans:
// BeanListProcessor converts each parsed row to an instance of a given class, then stores each instance into a list.
BeanListProcessor<SubscriberPackages> rowProcessor = new BeanListProcessor<SubscriberPackages>(SubscriberPackages.class);
CsvParserSettings parserSettings = new CsvParserSettings(); //many options here, check the tutorial.
parserSettings.setRowProcessor(rowProcessor); //uses the bean processor to handle your input rows
parserSettings.setHeaderExtractionEnabled(true); // extracts header names from the input file.
CsvParser parser = new CsvParser(parserSettings); //creates a parser with your settings.
parser.parse(new FileReader(new File("/path/to/file.csv"))); //all rows parsed here go straight to the bean processor
// The BeanListProcessor provides a list of objects extracted from the input.
List<SubscriberPackages> beans = rowProcessor.getBeans();
Disclosure: I am the author of this library. It's open-source and free (Apache V2.0 license).

libgdx Json parsing

hi I'm trying to get all 'id' value from my json into my 'results' array.
I didn't really understood how the json class of libgdx works, but I know how json works itself.
Here is the json : http://pastebin.com/qu71EnMx
Here is my code :
Array<Integer> results = new Array<Integer>();
Json jsonObject = new Json(OutputType.json);
JsonReader jsonReader = new JsonReader();
JsonValue jv = null;
JsonValue jv_array = null;
//
try {
String str = jsonObject.toJson(jsonString);
jv = jsonReader.parse(str);
} catch (SerializationException e) {
//show error
}
//
try {
jv_array = jv.get("table");
} catch (SerializationException e) {
//show error
}
//
for (int i = 0; i < jv_array.size; i++) {
//
try {
jv_array.get(i).get("name").asString();
results.add(new sic_PlayerInfos(
jv_array.get(i).get("id").asInt()
));
} catch (SerializationException e) {
//show error
}
}
Here is the error I get : 'Nullpointer' on jv_array.size

Doing it this way will result in a very hacky, not maintainable code. Your JSON file looks very simple but your code is terrible if you parse the whole JSON file yourself. Just imagine how it will look like if you are having more than an id, which is probably going to happen.
The much more clean way is object oriented. Create an object structure, which resembles the structure of your JSON file. In your case this might look like the following:
public class Data {
public Array<TableEntry> table;
}
public class TableEntry {
public int id;
}
Now you can easily deserialize the JSON with libgdx without any custom serializers, because libgdx uses reflection to handle most standard cases.
Json json = new Json();
json.setTypeName(null);
json.setUsePrototypes(false);
json.setIgnoreUnknownFields(true);
json.setOutputType(OutputType.json);
// I'm using your file as a String here, but you can supply the file as well
Data data = json.fromJson(Data.class, "{\"table\": [{\"id\": 1},{\"id\": 2},{\"id\": 3},{\"id\": 4}]}");
Now you've got a plain old java object (POJO) which contains all the information you need and you can process it however you want.
Array<Integer> results = new Array<Integer>();
for (TableEntry entry : data.table) {
results.add(entry.id);
}
Done. Very clean code and easily extendable.

confirmation email - create templae and combine it with an object

I need to implement email confirmation in my java web application. I am stuck with the email I have to send to the user.
I need to combine a template (of an confirmation email) with the User object and this will be the html content of the confirmation email.
I thought about using xslt as the template engine but I don't have xml form of the User object and don't really know how to create a xml from User instance.
I thought about jsp, but how do I render jsp page with an object and get the html as a result?
Any idea what packages I can use in order to create templae and combine it with an object?

I have used the following before. I seem to recall it wasn't complicated
http://velocity.apache.org/

How complex is the user object? If it's just five string-valued fields (say) you could simply supply these as string parameters to the transformation, avoiding the need to build XML from your Java data.
Alternatively, Java XSLT processors typically provide some way to invoke methods on Java objects from within the XSLT code. So you could supply the Java object as a parameter to the stylesheet and invoke its methods using extension functions. The details are processor-specific.

Instead of learning a new code, debug other's complicate code I decided to write my own small and suitable util:
public class StringTemplate {
private String filePath;
private String charsetName;
private Collection<AbstractMap.SimpleEntry<String, String>> args;
public StringTemplate(String filePath, String charsetName,
Collection<AbstractMap.SimpleEntry<String, String>> args) {
this.filePath = filePath;
this.charsetName=charsetName;
this.args = args;
}
public String generate() throws FileNotFoundException, IOException {
StringBuilder builder = new StringBuilder();
BufferedReader reader = new BufferedReader(new InputStreamReader(
getClass().getResourceAsStream(filePath),charsetName));
try {
String line = null;
while ((line = reader.readLine()) != null) {
builder.append(line);
builder.append(System.getProperty("line.separator"));
}
} finally {
reader.close();
}
for (AbstractMap.SimpleEntry<String, String> arg : this.args) {
int index = builder.indexOf(arg.getKey());
while (index != -1) {
builder.replace(index, index + arg.getKey().length(), arg.getValue());
index += arg.getValue().length();
index = builder.indexOf(arg.getKey(), index);
}
}
return builder.toString();
}
}