Display Message to User instead of empty JSON on HTML when records are empty in the database - html

Question

I have an application where I have an html page which takes user input through a textbox.This is a REST Spring Framework and is divided as Controller, Entity, Service, Repository, View and the main application class.
I take an input value and search in the Mongodb database, If the value is present, I return the entity object from Service to Controller. The controller returns the same Entity View object.- PersonView in this case. I get a JSON Data.
The above scenario works well as long as there are records in the database. In case if the record is not present, it returns an empty JSON. My Controller returns Person View Object and I do not wish to change the signature and make the return type as String since in that case it returns the address on my HTML page.
Considering this, how should I handle the case when there are no records in the database and I wish to display a message on this same HTML page saying there are no records available.
I tried throwing an exception but in this case too, how Do I display message on my HTML considering that my Controller returns JSON object and I do not wish to change its signature?
Controller Class is as below:
public PersonView searchPerson(#PathVariable String pname) {
List<Person> pList= PersonService.searchPerson(pname);
PersonView personView = new PersonView();
personView.setPersonView(pList);
return personView;
EDIT:
Here is the function from personView Class that I call in Controller:
public List<Person> setPersonView() {
this.personView = personView;
}
Here is the service Impl class:
public List<Person> searchPerson(String name) throws Exception {
List<Person> personlist= new ArrayList<Person>();
personlist = personRepository.findByName(name);
if (personlist.isEmpty())
throw new Exception("Records not found in the the database");
return personlist;
}

Answer 1

Create a custom Exception class:
public class EntityNotFoundException extends RuntimeException {
public EntityNotFoundException(String message) {
super(message);
}
}
Now, in you controller code:
public List<Person> searchPerson(String name) {
List<Person> personlist= new ArrayList<Person>();
personlist = personRepository.findByName(name);
if (personlist.isEmpty()) {
throw new EntityNotFoundException("Records not found in the the database");
}
return personlist;
}
After that you can try something like this in you controller class:
private static final MappingJacksonJsonView JSON_VIEW = new MappingJacksonJsonView();
#ExceptionHandler(EntityNotFoundException.class)
public ModelAndView handleNotFoundException( Exception ex )
{
return new ModelAndView(JSON_VIEW, "error", new ErrorMessage("No Record in Db") );
}
Your ErrorMessage class can be a simple POJO:
public class ErrorMessage {
private String message;
ErrorMessage(String message) {
this.message = message;
}
public String getMessage() {
return message;
}
}

Answer 2

Although already answered, I will add some points here.
Please note that at some point of time you will have a requirement to send the
headers, Response body (with different Objects). So consider using ResponseEntity Object which will be a wrapper to your List. Here is the sample code.
public ResponseEntity<List<Person>> searchPerson(String name) {
List<Person> personlist= new ArrayList<Person>();
personlist = personRepository.findByName(name);
if (personlist.isEmpty()) {
return new ResponseEntity(new EntityNotFoundException("Records not found in the the database"), HttpStatus.BAD_REQUEST);
}
return new ResponseEntity(personlist , HttpStatus.OK);
}
Response Entity Object provides flexibility to greater extent. Read the documentation here.
https://docs.spring.io/spring/docs/current/javadocapi/org/springframework/http/ResponseEntity.html