Exception Handling in Spring Boot REST

Exception Handling in Spring Boot REST | Exception Handling in Spring Boot REST can be done in the following ways:-

1. Default Error Message (Spring Boot REST) + @ResponseStatus
2. Customized Error Message – @ControllerAdvice, @ExceptionHandler

Among these customized error message is most commonly used. First, let us see the default error message of Spring Boot REST with @ResponseStatus then we will see the customized error message in Spring Boot REST with @ControllerAdvice and @ExceptionHandler.

Default Error Message (Spring Boot ReST) + @ResponseStatus

In this case, we are using the default message given by BasicErrorController.error() method => (ResponseEntity<T> type–> JSON) format.

Here, we can customize only the Status and message (but not the trace).

{
    "timestamp": "2020-09-03T07:56:41.693+00:00",
    "status": 404,
    "error": "Not Found",
    "trace": ....,
    "message": "EMPLOYEE NOT EXIST 50",
    "path": "/find/50"
}

Create a starter project and add the following dependencies:- Spring web, lombok, Spring Boot DevTools

// model class
@Data
@NoArgsConstructor
@AllArgsConstructor
public class Employee {
    private Integer eid;
    private String ename;
}

// Custom Exception
@ResponseStatus(code = HttpStatus.NOT_FOUND)
public class EmployeeNotFoundException extends RuntimeException {
    private static final long serialVersionUID = 1L;

    public EmployeeNotFoundException() {
        super();
    }
    
    public EmployeeNotFoundException(String message) {
        super(message);
    }
}

// Rest Controller
@RestController
public class EmployeeRestController {

    @GetMapping("/find/{id}")
    public ResponseEntity<Employee> getOneEmployee(
            @PathVariable Integer id) {
        if(id!=5)
            throw new EmployeeNotFoundException("EMPLOYEE NOT EXIST " + id);
        
        return ResponseEntity.ok(new Employee(id,"SAM"));
    }
}

Customized Error Message – @ControllerAdvice, @ExceptionHandler

In this case, we are defining one new Exception Handler class by using annotations:-

1. @ControllerAdvice:- At the Handler class level
2. @ExceptionHandler:- At method Level
3. ResponseEntity<T>:- Method ReturnType

@ControllerAdvice tells while execution if the application gets any exception in any controller then come to class having @ControllerAdvice. After that based on the Exception type use the appropriate method having @ExceptionHandler.

@RestControllerAdvice was introduced in Spring Framework 4.3 and if we use @RestControllerAdvice then we can remove @ControllerAdvice (from the class level) & @ResponseBody (from the method level).

// exception class
package com.knowprogram.demo.exception;
public class EmployeeNotFoundException extends RuntimeException {
    private static final long serialVersionUID = 1L;

    public EmployeeNotFoundException() {
        super();
    }
    
    public EmployeeNotFoundException(String message) {
        super(message);
    }
}

// model class
package com.knowprogram.demo.model;
@Data
@NoArgsConstructor
@AllArgsConstructor
public class Employee {

    private Integer eid;
    private String ename;
}

@Data
@NoArgsConstructor
@AllArgsConstructor
public class ErrorType {

    private String message;
    private String code;
    private String error;
    private String classType;
}

// exception handler class
//@ControllerAdvice
@RestControllerAdvice
public class MyExceptionHandler {

    @ExceptionHandler(EmployeeNotFoundException.class)
    //@ResponseBody // It converts the response into JSON format
    public ResponseEntity<ErrorType> handleEmpNotFoundEx(
            EmployeeNotFoundException ex) 
    {
        
        return new ResponseEntity<ErrorType>(
                 new ErrorType(
                        ex.getMessage(), 
                        "NO_EMP_FOUND", 
                        "DATA NOT FOUND FOR GIVEN ID", 
                        "Employee"
                ), 
                HttpStatus.BAD_REQUEST);
    }
    
}

Sample Response:-

{
    "message": "Employee Not Exist 5",
    "code": "No EMP Found",
    "error": "Data not found for given ID",
    "classType": "Employee"
}

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