Spring Boot @ExceptionHandler

last modified July 16, 2023

Spring Boot @ExceptionHandler tutorial shows how to handle exceptions with Spring @ExceptionHandler.

Spring is a popular Java application framework and Spring Boot is an evolution of Spring that helps create stand-alone, production-grade Spring based applications easily.

@ExceptionHandler is an annotation for handling exceptions in specific handler classes or handler methods. In Servlet environments, we can combine the @ExceptionHandler annotation with @ResponseStatus to define the response status for the HTTP response.

Spring Boot @ExceptionHandler example

In the following application, we demonstrate the usage of the @ExceptionHandler. A HTML link in the home page calls a controller's method, which either returns data or throws an exception.

build.gradle
...
src
├── main
│  ├── java
│  │  └── com
│  │  └── zetcode
│  │  ├── Application.java
│  │  ├── controller
│  │  │  └── MyController.java
│  │  ├── exception
│  │  │  └── MyDataException.java
│  │  └── service
│  │  ├── IDataService.java
│  │  └── MyDataService.java
│  └── resources
│  ├── static
│  │  ├── index.html
│  │  └── showError.html
│  └── templates
│  └── showData.ftlh
└── test
 ├── java
 └── resources

This is the project structure of the Spring application.

plugins {
 id 'org.springframework.boot' version '3.1.1'
 id 'io.spring.dependency-management' version '1.1.0'
 id 'java'
}
group = 'com.zetcode'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = '17'
repositories {
 mavenCentral()
}
dependencies {
 implementation 'org.springframework.boot:spring-boot-starter-web'
 implementation 'org.springframework.boot:spring-boot-starter-freemarker'
}

This is the Gradle build file. The spring-boot-starter-freemarker is a dependency for Freemarker template engine.

package com.zetcode.controller;
import com.zetcode.exception.MyDataException;
import com.zetcode.service.IDataService;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.servlet.ModelAndView;
import java.util.HashMap;
import java.util.Map;
@Controller
public class MyController {
 private final IDataService dataService;
 public MyController(IDataService dataService) {
 this.dataService = dataService;
 }
 @RequestMapping(value = "/getData")
 public ModelAndView getData() {
 var data = dataService.findAll();
 Map<String, Object> params = new HashMap<>();
 params.put("values", data);
 return new ModelAndView("showData", params);
 }
 @ExceptionHandler(MyDataException.class)
 public String handleError(MyDataException e) {
 return "redirect:/showError.html";
 }
}

The MyController's getData method calls a service method and stores the retrieved data into a list. The data is sent to the showData view. In case of a MyDataException, the controller redirects to an error page.

@ExceptionHandler(MyDataException.class)
public String handleError(MyDataException e) {
 return "redirect:/showError.html";
}

The handleError is decorated with @ExceptionHandler. The handler is activated for the MyDataException. In the body of the method, we redirect to the showError.html page.

package com.zetcode.exception;
public class MyDataException extends RuntimeException {
 public MyDataException(String message) {
 super(message);
 }
}

We define a custom MyDataException.

package com.zetcode.service;
import java.util.List;
public interface IDataService {
 List<String> findAll();
}

IDataService contains the contract method.

package com.zetcode.service;
import com.zetcode.exception.MyDataException;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import org.springframework.stereotype.Service;
@Service
public class MyDataService implements IDataService {
 @Override
 public List<String> findAll() {
 var r = new Random();
 if (r.nextBoolean()) {
 throw new MyDataException("Failed to retrieve data");
 }
 var data = new ArrayList<String>();
 data.add("yellow moon");
 data.add("brisk pace");
 data.add("empty bottle");
 data.add("beautiful weather");
 return data;
 }
}

MyDataService implements IDataService's findAll method. The method either returns data or throws a MyDataException.

var r = new Random();
if (r.nextBoolean()) {
 throw new MyDataException("Failed to retrieve data");
}

The findAll method randomly throws MyDataException. The exception is then handled in the controller.

var data = new ArrayList<>();
data.add("yellow moon");
data.add("brisk pace");
data.add("empty bottle");
data.add("beautiful weather");
return data;

When there is no exception, we return a list of strings.

<!DOCTYPE html>
<html>
 <head>
 <title>Home page</title>
 <meta charset="UTF-8">
 <meta name="viewport" content="width=device-width, initial-scale=1.0">
 </head>
 <body>
 <a href="/getData">Get data</a>
 </body>
</html>

This is the home page. It contains a link that calls our controller method to fetch some data.

<!DOCTYPE html>
<html>
 <head>
 <title>Error</title>
 <meta charset="UTF-8">
 <meta name="viewport" content="width=device-width, initial-scale=1.0">
 </head>
 <body>
 <p>Failed to retrieve data</p>
 </body>
</html>

This is an error page. It is shown when MyDataException is thrown.

<!DOCTYPE html>
<html>
 <head>
 <title>Data</title>
 <meta charset="UTF-8">
 <meta name="viewport" content="width=device-width, initial-scale=1.0">
 </head>
 <body>
 <h2>Data</h2>
 <ul>
 <#list values as val>
 <li><td>${val}</td></li>
 </#list>
 </ul>
 
 </body>
</html>

The showData.ftlh is a Freemarker template file which shows all retrieved data in an HTML list.

package com.zetcode;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
@SpringBootApplication
public class Application {
 public static void main(String[] args) {
 SpringApplication.run(Application.class, args);
 }
}

Application is the entry point which bootstraps Spring Boot application.

In this article we have shown how to handle exceptions in a Spring application with @ExceptionHandler.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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