SpringBoot : How to do Exception Handling in Rest Application

Points To Remember

There are three ways to do exception handling in spring boot application.

1. Global Level using -  @ControllerAdvice
2. Controller Level using - @ExceptionHandler 
3. Method Level using - try/catch  

Difference between @ExceptionHandler and @ControllerAdvice

How to do Exception Handling in Rest Application

To demonstrate Exception Handling we will make three Exceptions.

• BaseException that will be parent of all the Custom Exceptions.
• CustomException1 that extends Base Exception.
• CustomException2 that extends Base Exception.

We will create the following methods

• ex1() throws BaseException
• ex2() throws CustomException1
• ex3() throws CustomException2
• ex4() throws NullPointerException 
• ex5() throws NumberFormatException

and now we will see how we can handle these exceptions using above mentioned ways.

Way 1 : Global Exception Handling using @ControllerAdvice

Add a class with annotation @ControllerAdvice and @RestController. This will make the class return a Rest Response.

• @ControllerAdvice tells your spring application that this class will do the exception handling for your application.
• @RestController will make it a controller and let this class render the response.
• Use @ExceptionHandler annotation to define the class of Exception it will catch. (A Base class will catch all the Inherited and extended classes)
• You can set the response status for exception using @ResponseStatus annotation.

HomeController.class

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1. package com.ekiras.controller;  
2.   
3. import com.ekiras.exception.BaseException;  
4. import com.ekiras.exception.CustomException1;  
5. import com.ekiras.exception.CustomException2;  
6. import org.springframework.web.bind.annotation.ExceptionHandler;  
7. import org.springframework.web.bind.annotation.RequestMapping;  
8. import org.springframework.web.bind.annotation.RestController;  
9.   
10. /** 
11.  * @author ekansh 
12.  * @since 19/2/16 
13.  */  
14. @RestController  
15. @RequestMapping({"","/"})  
16. public class HomeController {  
17.   
18.     @RequestMapping("/ex1")  
19.     public String ex1(){  
20.         // will be catched by global exception handler method handleBaseException  
21.         throw new BaseException("Base Exception");  
22.     }  
23.   
24.     @RequestMapping("/ex2")  
25.     public String ex2(){  
26.         // will be catched by global exception handler method handleBaseException  
27.         throw new CustomException1();  
28.     }  
29.   
30.     @RequestMapping("/ex3")  
31.     public String ex3(){  
32.         // will be catched by global exception handler method handleBaseException  
33.         throw new CustomException2();  
34.     }  
35.   
36.     @RequestMapping("/ex4")  
37.     public String ex4(){  
38.         // will be catched by global exception handler method handleException  
39.         throw new NullPointerException("null pointer exception");  
40.     }  
41.   
42.     @RequestMapping("/ex5")  
43.     public String ex5(){  
44.         // will be catched by controller exception hnadler handler method nfeHandler  
45.         throw new NumberFormatException("number format exception");  
46.     }  
47.   
48.     /** 
49.      * This method will handle all the Number Format Exceptions that arise within this controller. 
50.      *  
51.      * */  
52.     @ExceptionHandler(value = NumberFormatException.class)  
53.     public String nfeHandler(NumberFormatException e){  
54.         return e.getMessage();  
55.     }  
56.   
57. }  

package com.ekiras.controller; import com.ekiras.exception.BaseException; import com.ekiras.exception.CustomException1; import com.ekiras.exception.CustomException2; import org.springframework.web.bind.annotation.ExceptionHandler; import org.springframework.web.bind.annotation.RequestMapping; import org.springframework.web.bind.annotation.RestController; /** * @author ekansh * @since 19/2/16 */ @RestController @RequestMapping({"","/"}) public class HomeController { @RequestMapping("/ex1") public String ex1(){ // will be catched by global exception handler method handleBaseException throw new BaseException("Base Exception"); } @RequestMapping("/ex2") public String ex2(){ // will be catched by global exception handler method handleBaseException throw new CustomException1(); } @RequestMapping("/ex3") public String ex3(){ // will be catched by global exception handler method handleBaseException throw new CustomException2(); } @RequestMapping("/ex4") public String ex4(){ // will be catched by global exception handler method handleException throw new NullPointerException("null pointer exception"); } @RequestMapping("/ex5") public String ex5(){ // will be catched by controller exception hnadler handler method nfeHandler throw new NumberFormatException("number format exception"); } /** * This method will handle all the Number Format Exceptions that arise within this controller. * * */ @ExceptionHandler(value = NumberFormatException.class) public String nfeHandler(NumberFormatException e){ return e.getMessage(); } }

GlobalExceptionHandler.class

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1. package com.ekiras.handler.exception;  
2.   
3. import com.ekiras.exception.BaseException;  
4. import org.springframework.http.HttpStatus;  
5. import org.springframework.web.bind.annotation.ControllerAdvice;  
6. import org.springframework.web.bind.annotation.ExceptionHandler;  
7. import org.springframework.web.bind.annotation.ResponseStatus;  
8. import org.springframework.web.bind.annotation.RestController;  
9.   
10. /** 
11.  * @author ekansh 
12.  * @since 19/2/16 
13.  */  
14. @ControllerAdvice  
15. @RestController  
16. public class GlobalExceptionHandler {  
17.   
18.     @ResponseStatus(HttpStatus.BAD_REQUEST)  
19.     @ExceptionHandler(value = BaseException.class)  
20.     public String handleBaseException(BaseException e){  
21.         return e.getMessage();  
22.     }  
23.   
24.     @ExceptionHandler(value = Exception.class)  
25.     public String handleException(Exception e){return e.getMessage();}  
26.   
27.   
28. }  

package com.ekiras.handler.exception; import com.ekiras.exception.BaseException; import org.springframework.http.HttpStatus; import org.springframework.web.bind.annotation.ControllerAdvice; import org.springframework.web.bind.annotation.ExceptionHandler; import org.springframework.web.bind.annotation.ResponseStatus; import org.springframework.web.bind.annotation.RestController; /** * @author ekansh * @since 19/2/16 */ @ControllerAdvice @RestController public class GlobalExceptionHandler { @ResponseStatus(HttpStatus.BAD_REQUEST) @ExceptionHandler(value = BaseException.class) public String handleBaseException(BaseException e){ return e.getMessage(); } @ExceptionHandler(value = Exception.class) public String handleException(Exception e){return e.getMessage();} }

Here,

• handleBaseException(BaseException e) ::  will catch all the exceptions for classes BaseException, CustomException1 and CustomException2.
• handleException(Exception e) ::  will handle all the exceptions that are childs of Exception class.

Note :: If BaseException or its child exception is thrown then handleBaseException() will catch this exception and not the handleException() method

Way 2 : Controller Level Exception handling using @ExceptionHandler

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1. @ExceptionHandler(value = NumberFormatException.class)  
2.  public String nfeHandler(NumberFormatException e){  
3.      return e.getMessage();  
4.  }  

@ExceptionHandler(value = NumberFormatException.class) public String nfeHandler(NumberFormatException e){ return e.getMessage(); }

The above code in the HomeController.java will catch will the NumberFormatException that arise from this controller. This will not handle NumberFormatException that occurs in any other controller.

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