[JAVA] Spring Boot exception handling

Spring Boot exception handling

Overview

In SpringBoot, exceptions can be handled by multiple methods such as exception handling using the SpringMVC function, SpringBoot AutoConfiguration and exception handling using the embedded server. Although it is stated in Official Reference, the range and mechanism that can be handled are a little difficult to understand. So I will summarize the main methods.

Exception handling method

List

HandlerExcepitonResolver HandlerExceptionResolver is an exception handling method that uses the functions of Spring MVC. Since it uses the SpringMVC function, it cannot be handled if an exception occurs in Filter or View.

A schematic diagram of handling is shown below.

HandlerExceptionResolver has multiple implementation classes shown below by default. In the table below, enable / disable indicates whether it is enabled or disabled by the default setting of Spring Boot, and the ExceptionResolver that comes above has priority.

The following shows the exception handling method by the most orthodox `ʻExceptionHandlerExceptionResolver``.

Handling by ExceptionHandlerExceptionResolver

When an exception occurs, the method with the @ExceptionHandler annotation to which the meta information of the exception class that occurred is added is scanned, and the process is transferred.

The method with @ExceptionHandler can be defined in the class with @Controller or @ControllerAdvice as shown below.

ThrowExceptionController.java

@Controller
@RequestMapping("web")
public class ThrowExceptionController {
	
	@GetMapping("original")
	public void throwOriginalException() {
		throw new OriginalWebException("thrown in ThrowExceptionController");

	}
	
	@ExceptionHandler(OriginalWebException.class)
	public String handleOriginalWebException(OriginalWebException exception) {
		return "OriginalWebException.html";
	}

}

TransverseExceptionHandler.java

@ControllerAdvice
public class ThrowExceptionController {
	
	@ExceptionHandler(OriginalWebException.class)
	public String handleOriginalWebException(OriginalWebException exception) {
		return "OriginalWebException.html";
	}

}

In the case of @Controller, exception handling is possible only for exceptions that occur in the same Controller, but in the case of @ControllerAdvice, all Controllers can be handled across the board.

If both @Controller and @ControllerAdvice can be handled, the one given to @Controller has priority.

ErrorPage

ErrorPage in SpringBoot is almost the same as ErrorPage element defined in Web.xml of conventional SpringFW.

ErrorPage maps the status code or exception class to the path so that it can be handled. A schematic diagram is shown below.

How to register ErrorPage can be done by creating an implementation class of ErrorPageRegistrar as shown below.

AddErrorPage.java

@Configuration
public class AddErrorPage implements ErrorPageRegistrar {

	@Override
	public void registerErrorPages(ErrorPageRegistry registry) {
		registry.addErrorPages(new ErrorPage(exception, path));

        // new ErrorPage(HttpStatusCode, path)But possible
	}
}

ErrorController ErrorController is an exception handling method provided by Spring Boot and is the most commonly used method of exception handling in Spring Boot. A schematic diagram is shown below.

If the exceptions that occur in the SpringBoot application are not handled, they are all supposed to be dispatched to the / error path by the ErrorPage function described above. By default, / error is mapped to the BasicErrorController class, and handling is performed there.

In BasicErrorController, handling returns HTML or JSON depending on the request header. In the case of HTML, WhiteLabelErrorPage is returned, and the returned contents are specified by ```ErrorAttributes. In the case of JSON, `ʻErrorAttributes is returned.

To customize the handling method by ʻErrorController``, create an implementation class of ʻErrorController. Also, if you want to customize the returned contents, implement the `ʻErrorAttributes class.

Summary

For exception handling in SpringBoot application, basically use `ʻErrorController, and if you want to perform finer handling, use HandlerExceptionResolver``.