Sixth Round of Improvements to the Reddit Application

1. Overview

In this article we’re going to be almost wrapping up the improvements to the Reddit application.

2. Command API Security

First, we’re going to do some work to secure the command API to prevent manipulating of resources by users other than the owner.

2.1. Configuration

We’re going to start by enabling the use of @Preauthorize in the configuration:

@EnableGlobalMethodSecurity(prePostEnabled = true)

2.2. Authorize Commands

Next, let’s authorize our commands in the controller layer with the help of some Spring Security expressions:

@PreAuthorize("@resourceSecurityService.isPostOwner(#postDto.id)")
@RequestMapping(value = "/{id}", method = RequestMethod.PUT)
@ResponseStatus(HttpStatus.OK)
public void updatePost(@RequestBody ScheduledPostUpdateCommandDto postDto) {
    ...
}

@PreAuthorize("@resourceSecurityService.isPostOwner(#id)")
@RequestMapping(value = "/{id}", method = RequestMethod.DELETE)
@ResponseStatus(HttpStatus.NO_CONTENT)
public void deletePost(@PathVariable("id") Long id) {
    ...
}

@PreAuthorize("@resourceSecurityService.isRssFeedOwner(#feedDto.id)")
@RequestMapping(value = "/{id}", method = RequestMethod.PUT)
@ResponseStatus(HttpStatus.OK)
public void updateFeed(@RequestBody FeedUpdateCommandDto feedDto) {
    ..
}

@PreAuthorize("@resourceSecurityService.isRssFeedOwner(#id)")
@RequestMapping(value = "/{id}", method = RequestMethod.DELETE)
@ResponseStatus(HttpStatus.NO_CONTENT)
public void deleteFeed(@PathVariable("id") Long id) {
    ...
}

Note that:

• We’re using “#” to access the method argument – as we did in #id
• We’re using “@” to access a bean – as we did in @resourceSecurityService

2.3. Resource Security Service

Here’s how the service responsible with checking the ownership looks like:

@Service
public class ResourceSecurityService {

    @Autowired
    private PostRepository postRepository;

    @Autowired
    private MyFeedRepository feedRepository;

    public boolean isPostOwner(Long postId) {
        UserPrincipal userPrincipal = (UserPrincipal) 
          SecurityContextHolder.getContext().getAuthentication().getPrincipal();
        User user = userPrincipal.getUser();
        Post post = postRepository.findOne(postId);
        return post.getUser().getId() == user.getId();
    }

    public boolean isRssFeedOwner(Long feedId) {
        UserPrincipal userPrincipal = (UserPrincipal) 
          SecurityContextHolder.getContext().getAuthentication().getPrincipal();
        User user = userPrincipal.getUser();
        MyFeed feed = feedRepository.findOne(feedId);
        return feed.getUser().getId() == user.getId();
    }
}

Note that:

• isPostOwner(): check if current user owns the Post with given postId
• isRssFeedOwner(): check if current user owns the MyFeed with given feedId

2.4. Exception Handling

Next, we will simply handle the AccessDeniedException – as follows:

@ExceptionHandler({ AuthenticationCredentialsNotFoundException.class, AccessDeniedException.class })
public ResponseEntity<Object> handleAccessDeniedException(final Exception ex, final WebRequest request) {
    logger.error("403 Status Code", ex);
    ApiError apiError = new ApiError(HttpStatus.FORBIDDEN, ex);
    return new ResponseEntity<Object>(apiError, new HttpHeaders(), HttpStatus.FORBIDDEN);
}

2.5. Authorization Test

Finally, we will test our command authorization:

public class CommandAuthorizationLiveTest extends ScheduledPostLiveTest {

    @Test
    public void givenPostOwner_whenUpdatingScheduledPost_thenUpdated() throws ParseException, IOException {
        ScheduledPostDto post = newDto();
        post.setTitle("new title");
        Response response = withRequestBody(givenAuth(), post).put(urlPrefix + "/api/scheduledPosts/" + post.getId());

        assertEquals(200, response.statusCode());
    }

    @Test
    public void givenUserOtherThanOwner_whenUpdatingScheduledPost_thenForbidden() throws ParseException, IOException {
        ScheduledPostDto post = newDto();
        post.setTitle("new title");
        Response response = withRequestBody(givenAnotherUserAuth(), post).put(urlPrefix + "/api/scheduledPosts/" + post.getId());

        assertEquals(403, response.statusCode());
    }

    private RequestSpecification givenAnotherUserAuth() {
        FormAuthConfig formConfig = new FormAuthConfig(
          urlPrefix + "/j_spring_security_check", "username", "password");
        return RestAssured.given().auth().form("test", "test", formConfig);
    }
}

Note how thegivenAuth() implementation is using the user “john”, while givenAnotherUserAuth() is using the user “test” – so that we can then test out these complex scenarios involving two different users.

3. More Resubmit Options

Next, we’ll add in an interesting option – resubmitting an article to Reddit after a day or two, instead of right awa.

We’ll start by modifying the scheduled post resubmit options and we’ll split timeInterval. This used to have two separate responsibilities; it was:

• the time between post submission and score check time and
• the time between score check and next submission time

We’ll not separate these two responsibilities: checkAfterInterval and submitAfterInterval.

3.1. The Post Entity

We will modify both Post and Preference entities by removing:

private int timeInterval;

And adding:

private int checkAfterInterval;

private int submitAfterInterval;

Note that we’ll do the same for the related DTOs.

3.2. The Scheduler

Next, we will modify our scheduler to use the new time intervals – as follows:

private void checkAndReSubmitInternal(Post post) {
    if (didIntervalPass(post.getSubmissionDate(), post.getCheckAfterInterval())) {
        PostScores postScores = getPostScores(post);
        ...
}

private void checkAndDeleteInternal(Post post) {
    if (didIntervalPass(post.getSubmissionDate(), post.getCheckAfterInterval())) {
        PostScores postScores = getPostScores(post);
        ...
}

private void resetPost(Post post, String failReason) {
    long time = new Date().getTime();
    time += TimeUnit.MILLISECONDS.convert(post.getSubmitAfterInterval(), TimeUnit.MINUTES);
    post.setSubmissionDate(new Date(time))
    ...
}

Note that, for a scheduled post with submissionDate T and checkAfterInterval t1 and submitAfterInterval t2 and number of attempts > 1, we’ll have:

1. Post is submitted for the first time at T
2. Scheduler checks the post score at T+t1
3. Assuming post didn’t reach goal score, the post is the submitted for the second time at T+t1+t2

4. Extra Checks for the OAuth2 Access Token

Next, we’ll add some extra checks around working with the access token.

Sometimes, the user access token could be broken which leads to unexpected behavior in the application. We’re going to fix that by allowing the user to re-connect their account to Reddit – thus receiving a new access token – if that happens.

4.1. Reddit Controller

Here’s the simple controller level check – isAccessTokenValid():

@RequestMapping(value = "/isAccessTokenValid")
@ResponseBody
public boolean isAccessTokenValid() {
    return redditService.isCurrentUserAccessTokenValid();
}

4.2. Reddit Service

And here’s the service level implementation:

@Override
public boolean isCurrentUserAccessTokenValid() {
    UserPrincipal userPrincipal = (UserPrincipal) 
      SecurityContextHolder.getContext().getAuthentication().getPrincipal();
    User currentUser = userPrincipal.getUser();
    if (currentUser.getAccessToken() == null) {
        return false;
    }
    try {
        redditTemplate.needsCaptcha();
    } catch (Exception e) {
        redditTemplate.setAccessToken(null);
        currentUser.setAccessToken(null);
        currentUser.setRefreshToken(null);
        currentUser.setTokenExpiration(null);
        userRepository.save(currentUser);
        return false;
    }
    return true;
}

What’s happening here is quite simple. If the user already has an access token, we’ll try to reach the Reddit API using the simple needsCaptcha call.

If the call fails, then the current token is invalid – so we’ll reset it. And of course this leads to the user being prompted to reconnect their account to Reddit.

4.3. Front-end

Finally, we’ll show this on the homepage:

<div id="connect" style="display:none">
    <a href="redditLogin">Connect your Account to Reddit</a>
</div>

<script>
$.get("api/isAccessTokenValid", function(data){
    if(!data){
        $("#connect").show();
    }
});
</script>

Note how, if the access token is invalid, the “Connect to Reddit” link will be shown to the user.

5. Separation into Multiple Modules

Next, we’re splitting the application into modules. We’ll go with 4 modules: reddit-common, reddit-rest, reddit-ui and reddit-web.

5.1. Parent

First, let’s start with our parent module which wrap all sub-modules.

The parent module reddit-scheduler contains sub-modules and a simple pom.xml – as follows:

<project>
    <modelVersion>4.0.0</modelVersion>
    <groupId>org.baeldung</groupId>
    <artifactId>reddit-scheduler</artifactId>
    <version>0.2.0-SNAPSHOT</version>
    <name>reddit-scheduler</name>
    <packaging>pom</packaging>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.2.7.RELEASE</version>
    </parent>
        
    <modules>
        <module>reddit-common</module>
        <module>reddit-rest</module>
        <module>reddit-ui</module>
        <module>reddit-web</module>
    </modules>

    <properties>
        <!-- dependency versions and properties -->
    </properties>

</project>

All properties and dependency versions will be declared here, in the parent pom.xml – to be used by all sub-modules.

5.2. Common Module

Now, let’s talk about our reddit-common module. This module will contain persistence, service and reddit related resources. It also contains persistence and integration tests.

The configuration classes included in this module are CommonConfig, PersistenceJpaConfig, RedditConfig, ServiceConfig, WebGeneralConfig.

Here’s the simple pom.xml:

<project>
    <modelVersion>4.0.0</modelVersion>
    <artifactId>reddit-common</artifactId>
    <name>reddit-common</name>
    <packaging>jar</packaging>

    <parent>
        <groupId>org.baeldung</groupId>
        <artifactId>reddit-scheduler</artifactId>
        <version>0.2.0-SNAPSHOT</version>
    </parent>

</project>

5.3. REST Module

Our reddit-rest module contains the REST controllers and the DTOs.

The only configuration class in this module is WebApiConfig.

Here’s the pom.xml:

<project>
    <modelVersion>4.0.0</modelVersion>
    <artifactId>reddit-rest</artifactId>
    <name>reddit-rest</name>
    <packaging>jar</packaging>

    <parent>
        <groupId>org.baeldung</groupId>
        <artifactId>reddit-scheduler</artifactId>
        <version>0.2.0-SNAPSHOT</version>
    </parent>

    <dependencies>
        <dependency>
            <groupId>org.baeldung</groupId>
            <artifactId>reddit-common</artifactId>
            <version>0.2.0-SNAPSHOT</version>
        </dependency>
    </dependencies>
    ...

This module contains all exception handling logic as well.

5.4. UI Module

The reddit-ui module contains the front-end and MVC controllers.

The configuration classes included are WebFrontendConfig and ThymeleafConfig.

We’ll need to change the Thymeleaf configuration to load templates from resources classpath instead of Server context:

@Bean
public TemplateResolver templateResolver() {
    SpringResourceTemplateResolver templateResolver = new SpringResourceTemplateResolver();
    templateResolver.setPrefix("classpath:/");
    templateResolver.setSuffix(".html");
    templateResolver.setCacheable(false);
    return templateResolver;
}

Here’s the simple pom.xml:

<project>
    <modelVersion>4.0.0</modelVersion>
    <artifactId>reddit-ui</artifactId>
    <name>reddit-ui</name>
    <packaging>jar</packaging>

    <parent>
        <groupId>org.baeldung</groupId>
        <artifactId>reddit-scheduler</artifactId>
        <version>0.2.0-SNAPSHOT</version>
    </parent>

    <dependencies>
        <dependency>
            <groupId>org.baeldung</groupId>
            <artifactId>reddit-common</artifactId>
            <version>0.2.0-SNAPSHOT</version>
        </dependency>
    </dependencies>
...

We now have a simpler exception handler here as well, for handling front-end exceptions:

@ControllerAdvice
public class RestExceptionHandler extends ResponseEntityExceptionHandler implements Serializable {

    private static final long serialVersionUID = -3365045939814599316L;

    @ExceptionHandler({ UserApprovalRequiredException.class, UserRedirectRequiredException.class })
    public String handleRedirect(RuntimeException ex, WebRequest request) {
        logger.info(ex.getLocalizedMessage());
        throw ex;
    }

    @ExceptionHandler({ Exception.class })
    public String handleInternal(RuntimeException ex, WebRequest request) {
        logger.error(ex);
        String response = "Error Occurred: " + ex.getMessage();
        return "redirect:/submissionResponse?msg=" + response;
    }
}

5.5. Web Module

Finally, here is our reddit-web module.

This module contains resources, security configuration and SpringBootApplication configuration – as follows:

@SpringBootApplication
public class Application extends SpringBootServletInitializer {
    @Bean
    public ServletRegistrationBean frontendServlet() {
        AnnotationConfigWebApplicationContext dispatcherContext = 
          new AnnotationConfigWebApplicationContext();
        dispatcherContext.register(WebFrontendConfig.class, ThymeleafConfig.class);
        ServletRegistrationBean registration = new ServletRegistrationBean(
          new DispatcherServlet(dispatcherContext), "/*");
        registration.setName("FrontendServlet");
        registration.setLoadOnStartup(1);
        return registration;
    }

    @Bean
    public ServletRegistrationBean apiServlet() {
        AnnotationConfigWebApplicationContext dispatcherContext = 
          new AnnotationConfigWebApplicationContext();
        dispatcherContext.register(WebApiConfig.class);
        ServletRegistrationBean registration = new ServletRegistrationBean(
          new DispatcherServlet(dispatcherContext), "/api/*");
        registration.setName("ApiServlet");
        registration.setLoadOnStartup(2);
        return registration;
    }

    @Override
    protected SpringApplicationBuilder configure(SpringApplicationBuilder application) {
        application.sources(Application.class, CommonConfig.class, 
          PersistenceJpaConfig.class, RedditConfig.class, 
          ServiceConfig.class, WebGeneralConfig.class);
        return application;
    }

    @Override
    public void onStartup(ServletContext servletContext) throws ServletException {
        super.onStartup(servletContext);
        servletContext.addListener(new SessionListener());
        servletContext.addListener(new RequestContextListener());
        servletContext.addListener(new HttpSessionEventPublisher());
    }

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

Here is pom.xml:

<project>
    <modelVersion>4.0.0</modelVersion>
    <artifactId>reddit-web</artifactId>
    <name>reddit-web</name>
    <packaging>war</packaging>

    <parent>
        <groupId>org.baeldung</groupId>
        <artifactId>reddit-scheduler</artifactId>
        <version>0.2.0-SNAPSHOT</version>
    </parent>

    <dependencies>
	<dependency>
            <groupId>org.baeldung</groupId>
            <artifactId>reddit-common</artifactId>
            <version>0.2.0-SNAPSHOT</version>
        </dependency>
        
        <dependency>
            <groupId>org.baeldung</groupId>
            <artifactId>reddit-rest</artifactId>
            <version>0.2.0-SNAPSHOT</version>
        </dependency>
        
        <dependency>
            <groupId>org.baeldung</groupId>
            <artifactId>reddit-ui</artifactId>
            <version>0.2.0-SNAPSHOT</version>
        </dependency>
...

Note that this is the only war, deployable module – so the application is well modularized now, but still deployed as a monolith.

6. Conclusion

We’re close to wrapping up the Reddit case study. It’s been a very cool app built from ground up around a personal need of mine, and it worked out quite well.