Micronaut REST Exception Handling - Global

Hello everyone, today we will learn how to handle exceptions in the Micronaut REST application using ExceptionHandler. You can download the source code from our Github Repository.

Project Directory:



Pom.xml:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" 
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 
         http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.knf.dev.demo</groupId>
  <artifactId>micronaut-global-exception-handling</artifactId>
  <version>0.1</version>
  <packaging>${packaging}</packaging>

  <parent>
    <groupId>io.micronaut</groupId>
    <artifactId>micronaut-parent</artifactId>
    <version>3.1.3</version>
  </parent>

  <properties>
    <packaging>jar</packaging>
    <jdk.version>11</jdk.version>
    <release.version>11</release.version>
    <micronaut.version>3.1.3</micronaut.version>
    <exec.mainClass>com.knf.dev.demo.Application</exec.mainClass>
    <micronaut.runtime>netty</micronaut.runtime>
  </properties>

  <repositories>
    <repository>
      <id>central</id>
      <url>https://repo.maven.apache.org/maven2</url>
    </repository>
  </repositories>

  <dependencies>
    <dependency>
      <groupId>io.micronaut</groupId>
      <artifactId>micronaut-inject</artifactId>
      <scope>compile</scope>
    </dependency>
    <dependency>
      <groupId>io.micronaut</groupId>
      <artifactId>micronaut-validation</artifactId>
      <scope>compile</scope>
    </dependency>
    <dependency>
      <groupId>org.junit.jupiter</groupId>
      <artifactId>junit-jupiter-api</artifactId>
      <scope>test</scope>
    </dependency>
    <dependency>
      <groupId>org.junit.jupiter</groupId>
      <artifactId>junit-jupiter-engine</artifactId>
      <scope>test</scope>
    </dependency>
    <dependency>
      <groupId>io.micronaut.test</groupId>
      <artifactId>micronaut-test-junit5</artifactId>
      <scope>test</scope>
    </dependency>
    <dependency>
      <groupId>io.micronaut</groupId>
      <artifactId>micronaut-http-client</artifactId>
      <scope>compile</scope>
    </dependency>
    <dependency>
      <groupId>io.micronaut</groupId>
      <artifactId>micronaut-http-server-netty</artifactId>
      <scope>compile</scope>
    </dependency>
    <dependency>
      <groupId>io.micronaut</groupId>
      <artifactId>micronaut-runtime</artifactId>
      <scope>compile</scope>
    </dependency>
    <dependency>
      <groupId>javax.annotation</groupId>
      <artifactId>javax.annotation-api</artifactId>
      <scope>compile</scope>
    </dependency>
    <dependency>
      <groupId>ch.qos.logback</groupId>
      <artifactId>logback-classic</artifactId>
      <scope>runtime</scope>
    </dependency>
  </dependencies>

  <build>
    <plugins>
      <plugin>
        <groupId>io.micronaut.build</groupId>
        <artifactId>micronaut-maven-plugin</artifactId>
      </plugin>
      
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-compiler-plugin</artifactId>
        <configuration>
          <annotationProcessorPaths combine.children="append">
            <path>
              <groupId>io.micronaut</groupId>
              <artifactId>micronaut-http-validation</artifactId>
              <version>${micronaut.version}</version>
            </path>
          </annotationProcessorPaths>
          <compilerArgs>
    <arg>-Amicronaut.processing.group=com.knf.dev.demo</arg>
          <arg>
 -Amicronaut.processing.module=micronaut-global-exception-handling
          </arg>
          </compilerArgs>
        </configuration>
      </plugin>
    </plugins>
  </build>
</project>



Create a POJO class:

package com.knf.dev.demo.model;

public class User {

    private String name;
    private String email;

    public User(String name, String email) {
        this.name = name;
        this.email = email;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }
}



Create an Error Message:

package com.knf.dev.demo.exception;

public class ErrorMessage {

    private String message;
    private Boolean status;

    public String getMessage() {
        return message;
    }

    public void setMessage(String message) {
        this.message = message;
    }

    public Boolean getStatus() {
        return status;
    }

    public void setStatus(Boolean status) {
        this.status = status;
    }
}



Create a data generator class:

package com.knf.dev.demo.data;

import java.util.HashMap;
import java.util.Map;
import com.knf.dev.demo.model.User;
import jakarta.inject.Singleton;

@Singleton
public class UserData {

    public User getUserById(Long id) {
        User user = genearteDummyData().get(id);
        return user;
    }

    // Generate Dummy Users
    private Map<Long, User> genearteDummyData() {

        Map<Long, User> dummyUsers = new HashMap<>();

        User user1 = new User("user-1", "user-1@gmail.com");
        User user2 = new User("user2", "user2@gmail.com");
        User user3 = new User("user3", "user3@gmail.com");

        dummyUsers.put(22l, user1);
        dummyUsers.put(13l, user2);
        dummyUsers.put(19l, user3);

        return dummyUsers;
    }
}


Create the Custom Exception:

package com.knf.dev.demo.exception;

import java.io.Serializable;

public class CustomException extends RuntimeException 
    implements Serializable {

    private static final long serialVersionUID = 1L;

    public CustomException() {
    }

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

    public CustomException(String message, Throwable cause) {
        super(message, cause);
    }

    public CustomException(Throwable cause) {
        super(cause);
    }

    public CustomException(String message, Throwable cause, 
         boolean enableSuppression, 
               boolean writableStackTrace) {
        
        super(message, cause, 
               enableSuppression, writableStackTrace);
    }
}


Create the Custom Exception Handler:

package com.knf.dev.demo.exception;

import io.micronaut.context.annotation.Requires;
import io.micronaut.http.HttpRequest;
import io.micronaut.http.HttpResponse;
import io.micronaut.http.HttpStatus;
import io.micronaut.http.annotation.Produces;
import io.micronaut.http.server.exceptions.ExceptionHandler;
import jakarta.inject.Singleton;

@Produces
@Singleton
@Requires(classes = { CustomException.class, ExceptionHandler.class })

public class CustomExceptionHandler 
         implements ExceptionHandler<CustomException, 
                HttpResponse<ErrorMessage>> {

    @Override
    public HttpResponse<ErrorMessage> 
        handle(HttpRequest request, CustomException exception) {

        ErrorMessage message = new ErrorMessage();
        message.setMessage(exception.getMessage());
        message.setStatus(false);
        return HttpResponse.serverError(message).
                status(HttpStatus.BAD_REQUEST);
    }
}



Create the User Controller class:

package com.knf.dev.demo.controller;

import com.knf.dev.demo.data.UserData;
import com.knf.dev.demo.exception.CustomException;
import com.knf.dev.demo.model.User;
import io.micronaut.http.annotation.Controller;
import io.micronaut.http.annotation.Get;

@Controller
public class UserController {

    protected final UserData userData;

    public UserController(UserData userData) {
        this.userData = userData;
    }

    @Get("/users/{id}")
    public User findUserById(String id) throws CustomException {
        Long user_id = null;
        try {
            user_id = Long.parseLong(id);
        } catch (NumberFormatException e) {
            throw new CustomException("User Id must be numeric");
        }
        User user = userData.getUserById(user_id);
        if (user == null) {
            throw new CustomException("Entity Not Found");
        }
        return user;
    }
}



Main

package com.knf.dev.demo;

import io.micronaut.runtime.Micronaut;

public class Application {

    public static void main(String[] args) {
        Micronaut.run(Application.class, args);
    }
}



Verify the REST APIs

Run as Java Application 

or

mvn mn:run


Invalid Request (Entity Not found):



Invalid Request(User Id must be numeric):



Valid request:

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