HandlerExceptionResolver로 예외처리 깔끔하게 처리하기

package hello.exception.resolver;

import com.fasterxml.jackson.databind.ObjectMapper;
import hello.exception.exception.UserException;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import lombok.extern.slf4j.Slf4j;
import org.springframework.web.servlet.HandlerExceptionResolver;
import org.springframework.web.servlet.ModelAndView;

import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

@Slf4j
public class UserHandlerExceptionResolver implements HandlerExceptionResolver {

    private final ObjectMapper objectMapper = new ObjectMapper();

    @Override
    public ModelAndView resolveException(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) {
        try{
            if(ex instanceof UserException){
                log.info("UserException resolver to 400");
                String acceptHeader = request.getHeader("accept");
                response.setStatus(HttpServletResponse.SC_BAD_REQUEST);

                if("application/json".equals(acceptHeader)){
                    Map<String,Object> errorResult = new HashMap<>();// 맵으로 에러를 키밸류로 담아준다.
                    errorResult.put("ex",ex.getClass());
                    errorResult.put("message",ex.getMessage());

                    String result = objectMapper.writeValueAsString(errorResult); //문자로 바꿔준다.

                    response.setContentType("application/json");
                    response.setCharacterEncoding("utf-8");
                    response.getWriter().write(result);
                    return new ModelAndView();
                }else{
                    //TEXT/HTML
                    return new ModelAndView("error/500");
                }

            }

        }catch (IOException e){
            log.error("resolver ex", e);
        }
        return null;
    }
}

서블릿에서 예외를 처리할 경우 복잡한 로직이 동원된다.

 

이에 HandlerExceptionResolver를 사용하면 편하다

 

예제

package hello.exception.resolver;

import com.fasterxml.jackson.databind.ObjectMapper;
import hello.exception.exception.UserException;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import lombok.extern.slf4j.Slf4j;
import org.springframework.web.servlet.HandlerExceptionResolver;
import org.springframework.web.servlet.ModelAndView;

import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

@Slf4j
public class UserHandlerExceptionResolver implements HandlerExceptionResolver {

    private final ObjectMapper objectMapper = new ObjectMapper();

    @Override
    public ModelAndView resolveException(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) {
        try{
            if(ex instanceof UserException){
                log.info("UserException resolver to 400");
                String acceptHeader = request.getHeader("accept");
                response.setStatus(HttpServletResponse.SC_BAD_REQUEST);

                if("application/json".equals(acceptHeader)){
                    Map<String,Object> errorResult = new HashMap<>();// 맵으로 에러를 키밸류로 담아준다.
                    errorResult.put("ex",ex.getClass());
                    errorResult.put("message",ex.getMessage());

                    String result = objectMapper.writeValueAsString(errorResult); //문자로 바꿔준다.

                    response.setContentType("application/json");
                    response.setCharacterEncoding("utf-8");
                    response.getWriter().write(result);
                    return new ModelAndView();
                }else{
                    //TEXT/HTML
                    return new ModelAndView("error/500");
                }

            }

        }catch (IOException e){
            log.error("resolver ex", e);
        }
        return null;
    }
}

package hello.exception;

import hello.exception.filter.LogFilter;
import hello.exception.interceptor.LogInterceptor;
import hello.exception.resolver.MyHandlerExceptionResolver;
import hello.exception.resolver.UserHandlerExceptionResolver;
import jakarta.servlet.DispatcherType;
import jakarta.servlet.Filter;
import org.springframework.boot.web.servlet.FilterRegistrationBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.HandlerExceptionResolver;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;

import java.util.List;

@Configuration
public class WebConfig implements WebMvcConfigurer {

    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(new LogInterceptor())
                .order(1)
                .addPathPatterns("/**")
                .excludePathPatterns("/css/*","*.ico","/error","/error-page/**"); //Filter와 다르게 DispatcherType을 넣을 수 없다.
                // 대신 excludePathPatterns 이라는 강력한 메소드가 있어서 error-page 관련을 빼면 된다.

    }

    @Override
    public void extendHandlerExceptionResolvers(List<HandlerExceptionResolver> resolvers) {
        resolvers.add(new MyHandlerExceptionResolver());
        resolvers.add(new UserHandlerExceptionResolver());
    }

    //@Bean
    public FilterRegistrationBean logFilter(){
        FilterRegistrationBean<Filter> filterRegistrationBean = new FilterRegistrationBean<>();
        filterRegistrationBean.setFilter(new LogFilter());
        filterRegistrationBean.setOrder(1);
        filterRegistrationBean.addUrlPatterns("/*");
        filterRegistrationBean.setDispatcherTypes(DispatcherType.REQUEST,DispatcherType.ERROR); //요청과 에러일 경우에만 호출된다.

        return filterRegistrationBean;
    }

}

등록 코드

@Override
public void extendHandlerExceptionResolvers(List<HandlerExceptionResolver> resolvers) {
    resolvers.add(new MyHandlerExceptionResolver());
    resolvers.add(new UserHandlerExceptionResolver());
}