We Keep Coding

Variables are not coming up null during Postman call

Setting up an Java Postman call assigning values to the variables but its shows null.
#PostMapping("/caStudents/student")
public String generateSignedValue(#RequestBody StudentRequest studentRequest) throws Exception
String signedValue=studentService.getSignedValue(studentRequest);
return signedValue;
My Pojo Student Class
public class StudentRequest {
String user;
Long duration ;
public String getPublicKey() {
return publicKey;
}
public void setPublicKey(String publicKey) {
this.publicKey = publicKey;
}
public String getUser() {
return user;
}
public void setUser(String user) {
this.user = user;
}
public Long getDuration() {
return duration;
}
public void setDuration(Long duration) {
this.duration = duration;
}
Postman Request
{"studentRequest":[{"user":"admin","duration":19336}]}

your request body should be like this:
{"user":"admin","duration":19336}
because you are getting StudentRequest as RequestBody and it means you should send StudentRequest internal properties not containing StudentRequest it self in request ,
second problem is that your RequestBody contains singular object not array .

According to what you've given us your request should actually be
{
"user": "admin",
"duration": 19336
}
If you want to provide multiple student requests at once (within an array), then you're StudenRequest class should look somewhat like this:
public class StudentRequest {
List<StudentR>;
// Getter and Setter or not in case you use lombok
class StudenR {
String user;
Long duration ;
}
}

Jackson custom serializer and deserializer with conditions

I am unable to find the correct way to manipulate the casing of a value via a custom annotation that I can control conditionally.
I have already looked into Jackson tutorials online with JsonFilters, Serialization, Deserialization - I have had most of them working but not with my desired outcome.
Custom Serializer:
public class CaseSerializer extends JsonSerializer<String> {
private boolean myCheck;
public CaseSerializer() {
// default
}
public CaseSerializer(boolean myControl) {
this.myCheck = myControl;
}
#Override
public void serialize(String value, JsonGenerator generator, SerializerProvider provider) throws IOException {
if (value != null) {
if (myCheck) {
generator.writeString(value.toUpperCase());
} else {
generator.writeString(value);
}
}
}
}
Person Model:
public class Person {
#JsonSerialize(using = CaseSerializer.class)
private String title;
private String firstName;
private String lastName;
public Person(String title, String firstName, String lastName) {
this.title = title;
this.firstName = firstName;
this.lastName = lastName;
}
// getters, setters & toString
}
Usage:
Person person = new Person("dr", "john", "doe");
SimpleModule module = new SimpleModule();
module.addSerializer(String.class,new CaseSerializer(true));
ObjectMapper mapper = new ObjectMapper();
mapper.registerModule(module);
String titleShouldBeUpper = mapper.writeValueAsString(person);
System.out.println(titleShouldBeUpper);
From running the code provided I expect that the title field within the Person class to be uppercased and the other values to remain as they were.
(CaseSerializer(true) meaning I want to uppercase the values)
This is not the case as the code prints the following output:
{"title":"dr","firstName":"JOHN","lastName":"DOE"}
When I run the code with the CaseSerializer() without the boolean myControl set to true, the expected output is that none of the fields are uppercased.
Which is what is happening:
{"title":"dr","firstName":"john","lastName":"doe"}
This means by default nothing will change.
If I call the mapper with a true for case serialization I only want the fields where the JsonSerialize(using = CaseSerializer.class) is present.
Any ideas?

Convert Json to List Java

I have a JSON array like this :
[
{"_id": {"$oid":"57e9e4b1f36d281c4b330509"}, "user": "edmtdev" },
{"_id": {"$oid":"57e9e4cec2ef164375c4c292"}, "user": "admin1234" },
{"_id": {"$oid":"57ea1b0ac2ef164375c5ff1e"}, "username": "admin34" }
]
This is my User.class, used to store all data:
public class User{
private Id id;
private String user;
public Id getId() {
return id;
}
public void setId(Id id) {
this.id = id;
}
public String getUser() {
return user;
}
public void setUser(String user) {
this.user = user;
}
}
And my Id.class, used to store the ID:
public class Id {
private String $oid;
public String get$oid() {
return $oid;
}
public void set$oid(String $oid) {
this.$oid = $oid;
}
}
I am using GSON in Java to get my users as a List<User>:
List<User> users = new ArrayList<User>();
Gson gson = new Gson();
Type listType = new TypeToken<List<User>>(){}.getType();
users = gson.fromJson(s,listType);
The problem is, I get users with username but no ID, $oid is not registered. Can someone help me understanding what does not work in this piece of code ?

You must replace id in User class by:
private Id _id;
because your json is _id, not id. And your json string at the end is wrong, is user, not username

#SerializedName("_id")
private Id id;
This is another approach.You can use this above annotation also.

Mapping JSON into POJO using Gson

I have the following JSON to represent the server response for a salt request:
{
"USER":
{
"E_MAIL":"email",
"SALT":"salt"
},
"CODE":"010"
}
And i tried to map it with the following POJO:
public class SaltPOJO {
private String code = null;
private User user = null;
#Override
public String toString() {
return this.user.toString();
}
public String getCode() {
return code;
}
public void setCode(String code) {
this.code = code;
}
public User getUser() {
return user;
}
public void setUser(User user) {
this.user = user;
}
public class User {
private String e_mail = null;
private String salt = null;
#Override
public String toString() {
return this.e_mail + ": " + this.salt;
}
public String getE_mail() {
return e_mail;
}
public void setE_mail(String e_mail) {
this.e_mail = e_mail;
}
public String getSalt() {
return salt;
}
public void setSalt(String salt) {
this.salt = salt;
}
}
}
Now everytime i do this:
Gson gson = new Gson();
SaltPOJO saltPojo = gson.fromJson(json.toString(), SaltPOJO.class);
Log.v("Bla", saltPojo.toString());
The saltPojo.toString() is null. How can i map my JSON into POJO using Gson?
Is the order of my variables important for the Gson mapping?

Is the order of my variables important for the Gson mapping?
No, that's not the case.
How can i map my JSON into POJO using Gson?
It's Case Sensitive and the keys in JSON string should be same as variable names used in POJO class.
You can use #SerializedName annotation to use any variable name as your like.
Sample code:
class SaltPOJO {
#SerializedName("CODE")
private String code = null;
#SerializedName("USER")
private User user = null;
...
class User {
#SerializedName("E_MAIL")
private String e_mail = null;
#SerializedName("SALT")
private String salt = null;

You don't have proper mapping between your getter and setter. If you change your json to something like below, it would work:
{
"user":
{
"email":"email",
"salt":"salt"
},
"code":"010"
}
If you are getting json form third party then unfortunately, you would have to change your pojo or you could use adapter.

Datastructure to store an nested element in JSON

I am modelling classes in Java to store a JSON , for a particular JSON
"id":1,
"firstName":"sample",
"lastName":"person",
"Books":{
"bookName":"gone with the wind"
"isbn": 12345
}
I created a class person with int id , String firstName etc...
what would be the best way to store bookName , make a class Books with a String bookName and int isbn , how would I represent books in the person class , As an array? since books always has only one value is there a better way to represent it

For json serialization/deserialization, I suggest the jackson library.Here is my code,it works fine on my computer!
I store the json in the file named json.data as following:
{"id":1,
"firstName":"sample",
"lastName":"person",
"books":[{"bookName":"gone with the wind","isbn":12345}]
}
And the code,I omitted the getter/setter to be short
public class Book
{
private String bookName;
private int isbn;
}
public class BookWriter
{
private String id;
private String firstName;
private String lastName;
private Book[] books;
}
public class JSONTest
{
public static void main(String[] args)
{
try
{
ObjectMapper mapper = new ObjectMapper();
BookWriter writer=(BookWriter)mapper.readValue(new File("json.data"), BookWriter.class);
for(Book book:writer.getBooks())
{
System.out.println(book.getBookName()+","+book.getIsbn());
}
} catch (Exception e)
{
e.printStackTrace();
}
}
}