[et_pb_section fb_built=”1″ fullwidth=”on” _builder_version=”4.4.1″][et_pb_fullwidth_post_title meta=”off” featured_placement=”background” _builder_version=”4.7.7″ title_font=”||||||||” title_text_color=”#ff6317″ title_font_size=”3.5em” meta_font=”|300|||||||” meta_text_color=”#ffffff” meta_font_size=”1em” background_enable_color=”off” use_background_color_gradient=”on” background_color_gradient_start=”rgba(248,248,248,0.85)” background_color_gradient_end=”rgba(248,248,248,0.75)” background_color_gradient_overlays_image=”on” min_height=”20vh” height=”400px” custom_padding=”6vh||6vh||false|false” global_module=”403″ locked=”off”][\/et_pb_fullwidth_post_title][\/et_pb_section][et_pb_section fb_built=”1″ admin_label=”intro” _builder_version=”4.4.6″ custom_padding=”|||0px||” locked=”off”][et_pb_row use_custom_gutter=”on” _builder_version=”4.4.6″ custom_margin=”||||false|false” custom_padding=”6vh||||false|false” border_color_left=”rgba(0,0,0,0)”][et_pb_column type=”4_4″ _builder_version=”4.4.1″][et_pb_text _builder_version=”4.7.7″ text_font=”||||||||” text_font_size=”1.1em” text_line_height=”1.6em” quote_font=”|700|||||||” quote_text_align=”left” quote_font_size=”16px” header_2_text_color=”#ff6317″ header_2_font_size=”1.5em” header_2_line_height=”0.9em” header_3_font_size=”23px” header_4_font=”||||||||” header_4_font_size=”16px” header_4_line_height=”1.5em” header_5_font_size=”14px” custom_margin=”||||false|false” custom_padding=”||||false|false” hover_enabled=”0″ border_color_left=”#ff6317″ sticky_enabled=”0″]<\/p>\n
In this article, we will show you how to take advantage of async processes in REST applications with Java Spring.\u00a0In a previous article<\/a>, we discussed how important it is for the software development<\/a> team to understand a software solution\/product\u2019s business logic, and its target functions and features. The main results are a hard focus on what matters most from a business perspective; less reworking; and clean release plans.<\/p>\n But understanding a software solution<\/a>\/product\u2019s goals can also influence some of the small details \u2013 for example, what happens when the user clicks a button or link. In the most straightforward scenario, the desired action is executed, and the result is reached\/displayed right away (i.e., following a synchronous process). In other cases, the user might need to wait for a result and have parts of the interface temporarily inaccessible\/disabled (i.e., during an async process).<\/p>\n The wait\/no-wait cases are decided by the product owner and implemented by the software development team as mutually exclusive sync\/async processes:<\/p>\n Async processes can be used\/implemented in many different ways. We look into five concrete situations:<\/p>\n [\/et_pb_text][\/et_pb_column][\/et_pb_row][et_pb_row use_custom_gutter=”on” _builder_version=”4.7.7″ custom_margin=”||||false|false” custom_padding=”6vh||||false|false” border_color_left=”rgba(0,0,0,0)”][et_pb_column type=”4_4″ _builder_version=”4.4.1″][et_pb_text _builder_version=”4.7.7″ text_font=”||||||||” text_font_size=”1.1em” text_line_height=”1.6em” quote_font=”|700|||||||” quote_text_align=”left” quote_font_size=”16px” header_2_text_color=”#ff6317″ header_2_font_size=”1.5em” header_2_line_height=”0.9em” header_3_font_size=”23px” header_4_font=”||||||||” header_4_font_size=”16px” header_4_line_height=”1.5em” header_5_font_size=”14px” custom_margin=”||||false|false” custom_padding=”||||false|false” hover_enabled=”0″ border_color_left=”#ff6317″ sticky_enabled=”0″]<\/p>\n Some of the users will do operations that involve other users as well \u2013 for example, leaving a comment on an item created by somebody else. In this case, we want to save the comment in the backend and notify the item\u2019s author about the new comment. Therefore, when the user clicks on \u201csave comment\u201d, the single backend call will do 2 things: save the actual comment and send an email to the item creator.<\/p>\n Saving the actual comment is done instantly, as the requesting user needs the feedback that it was saved. But sending the email is not something that concerns the requesting user, so the backend will trigger an async process, without waiting for the actual result. This means a faster response time for the users and not bothering them with error messages if something goes wrong while sending the email.<\/p>\n [\/et_pb_text][\/et_pb_column][\/et_pb_row][et_pb_row _builder_version=”4.7.7″ custom_margin=”||||false|false” custom_padding=”20px||0px||false|false” border_color_left=”rgba(0,0,0,0)” locked=”off”][et_pb_column type=”4_4″ _builder_version=”4.4.1″][et_pb_gallery gallery_ids=”7291″ fullwidth=”on” hover_icon=”%%186%%” _builder_version=”4.7.7″ _module_preset=”default” max_width=”65%” module_alignment=”left”][\/et_pb_gallery][et_pb_code _builder_version=”4.7.7″ _module_preset=”default”][\/et_pb_code][\/et_pb_column][\/et_pb_row][et_pb_row use_custom_gutter=”on” _builder_version=”4.7.7″ custom_margin=”||||false|false” custom_padding=”20px||0px||false|true” border_color_left=”rgba(0,0,0,0)” locked=”off”][et_pb_column type=”4_4″ _builder_version=”4.4.1″][et_pb_text _builder_version=”4.7.7″ text_font=”||||||||” text_font_size=”1.1em” text_line_height=”1.6em” quote_font=”|700|||||||” quote_text_align=”left” quote_font_size=”16px” header_2_text_color=”#ff6317″ header_2_font_size=”1.5em” header_2_line_height=”0.9em” header_3_font_size=”23px” header_4_font=”||||||||” header_4_font_size=”16px” header_4_line_height=”1.5em” header_5_font_size=”14px” custom_margin=”20px||||false|false” custom_padding=”||||false|false” border_color_left=”#ff6317″]Here is a code example for a backend flow, in the service that handles the comment saving:[\/et_pb_text][et_pb_text _builder_version=”4.7.7″ text_font=”|300|||||||” text_font_size=”1em” text_line_height=”1.3em” quote_font=”|700|||||||” quote_text_align=”left” quote_font_size=”1em” header_2_text_color=”#ff6317″ header_2_font_size=”1.5em” header_2_line_height=”0.9em” header_3_font_size=”23px” header_4_font=”||||||||” header_4_font_size=”16px” header_4_line_height=”1.5em” header_5_font_size=”14px” background_color=”#f8f8f8″ custom_margin=”20px|||20px|false|false” custom_padding=”||||false|false” border_color_left=”rgba(0,0,0,0)” border_style_left=”none” locked=”off”]<\/p>\n [\/et_pb_text][et_pb_text _builder_version=”4.7.7″ text_font=”||||||||” text_font_size=”1.1em” text_line_height=”1.6em” quote_font=”|700|||||||” quote_text_align=”left” quote_font_size=”16px” header_2_text_color=”#ff6317″ header_2_font_size=”1.5em” header_2_line_height=”0.9em” header_3_font_size=”23px” header_4_font=”||||||||” header_4_font_size=”16px” header_4_line_height=”1.5em” header_5_font_size=”14px” custom_margin=”20px||||false|false” custom_padding=”||||false|false” border_color_left=”#ff6317″]You can see that mailService.sendCommentSavedNotification(\u2026)<\/em> looks just like a normal method call. But because of the @Async annotation on the actual method implementation, Spring comes in and does something behind the scenes: it uses a ThreadExecutor<\/em> to spawn a new thread. (The actual execution of this method will happen on that new thread.) Therefore, the call mailService.sendCommentSavedNotification<\/em> will return instantly. The thread executor, if not defined explicitly in the application, will be the Spring default one (SimpleAsyncTaskExecutor<\/em>) and the only thing that you need to do is enable it in a configuration file like this:[\/et_pb_text][et_pb_text _builder_version=”4.7.7″ text_font=”|300|||||||” text_font_size=”1em” text_line_height=”1.3em” quote_font=”|700|||||||” quote_text_align=”left” quote_font_size=”1em” header_2_text_color=”#ff6317″ header_2_font_size=”1.5em” header_2_line_height=”0.9em” header_3_font_size=”23px” header_4_font=”||||||||” header_4_font_size=”16px” header_4_line_height=”1.5em” header_5_font_size=”14px” background_color=”#f8f8f8″ custom_margin=”20px|||20px|false|false” custom_padding=”||||false|false” border_color_left=”rgba(0,0,0,0)” border_style_left=”none” locked=”off”]<\/p>\n [\/et_pb_text][\/et_pb_column][\/et_pb_row][et_pb_row use_custom_gutter=”on” _builder_version=”4.7.7″ custom_margin=”||||false|false” custom_padding=”6vh||||false|false” border_color_left=”rgba(0,0,0,0)”][et_pb_column type=”4_4″ _builder_version=”4.4.1″][et_pb_text _builder_version=”4.7.7″ text_font=”||||||||” text_font_size=”1.1em” text_line_height=”1.6em” quote_font=”|700|||||||” quote_text_align=”left” quote_font_size=”16px” header_2_text_color=”#ff6317″ header_2_font_size=”1.5em” header_2_line_height=”0.9em” header_3_font_size=”23px” header_4_font=”||||||||” header_4_font_size=”16px” header_4_line_height=”1.5em” header_5_font_size=”14px” custom_margin=”||||false|false” custom_padding=”||||false|false” border_color_left=”#ff6317″]<\/p>\n Another usage case is uploading multiple documents at once, in order to attach them to an item. The documents might reside on a third-party server, which means uploading can take some time to complete. While waiting, the user can see a loading bar, and be able to cancel the action.<\/p>\n How does this work?<\/p>\n The frontend sends the documents to the backend and receives a process ID. With this process ID, the frontend can cancel the document uploading at any time (upon the user clicking the Cancel button) by doing a cancel call and passing the process ID.<\/p>\n This can only happen because the document uploading is asynchronous in the backend, and the backend can return the process ID before the upload finishes. In order for the documents upload process to support the cancelation, it has to actively check for any cancel actions, and it needs to know when it\u2019s finished.<\/p>\n We therefore get a more complex process that can be started, finished, or canceled. All these process states are kept in an event table that is used by both the frontend and the backend to track its progress and to show a result to the user when finished (successfully or with errors).[\/et_pb_text][\/et_pb_column][\/et_pb_row][et_pb_row _builder_version=”4.7.7″ custom_margin=”||||false|false” custom_padding=”20px||0px||false|false” border_color_left=”rgba(0,0,0,0)” locked=”off”][et_pb_column type=”4_4″ _builder_version=”4.4.1″][et_pb_gallery gallery_ids=”7299″ fullwidth=”on” hover_icon=”%%186%%” _builder_version=”4.7.7″ _module_preset=”default” max_width=”65%” module_alignment=”left”][\/et_pb_gallery][et_pb_code _builder_version=”4.7.7″ _module_preset=”default”][\/et_pb_code][\/et_pb_column][\/et_pb_row][et_pb_row use_custom_gutter=”on” _builder_version=”4.7.7″ custom_margin=”||||false|false” custom_padding=”20px||0px||false|true” border_color_left=”rgba(0,0,0,0)” locked=”off”][et_pb_column type=”4_4″ _builder_version=”4.4.1″][et_pb_text _builder_version=”4.7.7″ text_font=”||||||||” text_font_size=”1.1em” text_line_height=”1.6em” quote_font=”|700|||||||” quote_text_align=”left” quote_font_size=”16px” header_2_text_color=”#ff6317″ header_2_font_size=”1.5em” header_2_line_height=”0.9em” header_3_font_size=”23px” header_4_font=”||||||||” header_4_font_size=”16px” header_4_line_height=”1.5em” header_5_font_size=”14px” custom_margin=”20px||||false|false” custom_padding=”||||false|false” border_color_left=”#ff6317″]Here is a code example of the backend endpoints to be used by the frontend:[\/et_pb_text][et_pb_text _builder_version=”4.7.7″ text_font=”|300|||||||” text_font_size=”1em” text_line_height=”1.3em” quote_font=”|700|||||||” quote_text_align=”left” quote_font_size=”1em” header_2_text_color=”#ff6317″ header_2_font_size=”1.5em” header_2_line_height=”0.9em” header_3_font_size=”23px” header_4_font=”||||||||” header_4_font_size=”16px” header_4_line_height=”1.5em” header_5_font_size=”14px” background_color=”#f8f8f8″ custom_margin=”20px|||20px|false|false” custom_padding=”||||false|false” border_color_left=”rgba(0,0,0,0)” border_style_left=”none” locked=”off”]<\/p>\n [\/et_pb_text][et_pb_text _builder_version=”4.7.7″ text_font=”||||||||” text_font_size=”1.1em” text_line_height=”1.6em” quote_font=”|700|||||||” quote_text_align=”left” quote_font_size=”16px” header_2_text_color=”#ff6317″ header_2_font_size=”1.5em” header_2_line_height=”0.9em” header_3_font_size=”23px” header_4_font=”||||||||” header_4_font_size=”16px” header_4_line_height=”1.5em” header_5_font_size=”14px” custom_margin=”20px||||false|false” custom_padding=”||||false|false” border_color_left=”#ff6317″]As you can see, we have used:<\/p>\n [\/et_pb_text][\/et_pb_column][\/et_pb_row][et_pb_row use_custom_gutter=”on” _builder_version=”4.7.7″ custom_margin=”||||false|false” custom_padding=”6vh||||false|false” border_color_left=”rgba(0,0,0,0)”][et_pb_column type=”4_4″ _builder_version=”4.4.1″][et_pb_text _builder_version=”4.7.7″ text_font=”||||||||” text_font_size=”1.1em” text_line_height=”1.6em” quote_font=”|700|||||||” quote_text_align=”left” quote_font_size=”16px” header_2_text_color=”#ff6317″ header_2_font_size=”1.5em” header_2_line_height=”0.9em” header_3_font_size=”23px” header_4_font=”||||||||” header_4_font_size=”16px” header_4_line_height=”1.5em” header_5_font_size=”14px” custom_margin=”||||false|false” custom_padding=”||||false|false” border_color_left=”#ff6317″]<\/p>\n Another usage scenario: the user wants to perform an action, but the backend must check if (s)he is authorised, before actually executing the requests. Depending on the context, the authorisation might not be straightforward, and complex calculations might be needed. In our example below, the authorisation must be checked in multiple places \/ across multiple services, with each microservice providing its own authorisation result.<\/p>\n More specific: an application user wants to post a comment on an existing item (see 1. above). Depending on the business logic, only specific users might be permitted to post comments. In order to check a user\u2019s permissions, the backend might have to do multiple calls to different microservices. To speed it up, all those calls should be initiated in parallel.[\/et_pb_text][\/et_pb_column][\/et_pb_row][et_pb_row _builder_version=”4.7.7″ custom_margin=”||||false|false” custom_padding=”20px||0px||false|false” border_color_left=”rgba(0,0,0,0)” locked=”off”][et_pb_column type=”4_4″ _builder_version=”4.4.1″][et_pb_gallery gallery_ids=”7305″ fullwidth=”on” hover_icon=”%%186%%” _builder_version=”4.7.7″ _module_preset=”default” max_width=”65%” module_alignment=”left”][\/et_pb_gallery][et_pb_code _builder_version=”4.7.7″ _module_preset=”default”][\/et_pb_code][\/et_pb_column][\/et_pb_row][et_pb_row use_custom_gutter=”on” _builder_version=”4.7.7″ custom_margin=”||||false|false” custom_padding=”20px||0px||false|true” border_color_left=”rgba(0,0,0,0)” locked=”off”][et_pb_column type=”4_4″ _builder_version=”4.4.1″][et_pb_text _builder_version=”4.7.7″ text_font=”||||||||” text_font_size=”1.1em” text_line_height=”1.6em” quote_font=”|700|||||||” quote_text_align=”left” quote_font_size=”16px” header_2_text_color=”#ff6317″ header_2_font_size=”1.5em” header_2_line_height=”0.9em” header_3_font_size=”23px” header_4_font=”||||||||” header_4_font_size=”16px” header_4_line_height=”1.5em” header_5_font_size=”14px” custom_margin=”20px||||false|false” custom_padding=”||||false|false” border_color_left=”#ff6317″]Here\u2019s Java\u2019s CompletableFuture<\/em> to the rescue:[\/et_pb_text][et_pb_text _builder_version=”4.7.7″ text_font=”|300|||||||” text_font_size=”1em” text_line_height=”1.3em” quote_font=”|700|||||||” quote_text_align=”left” quote_font_size=”1em” header_2_text_color=”#ff6317″ header_2_font_size=”1.5em” header_2_line_height=”0.9em” header_3_font_size=”23px” header_4_font=”||||||||” header_4_font_size=”16px” header_4_line_height=”1.5em” header_5_font_size=”14px” background_color=”#f8f8f8″ custom_margin=”20px|||20px|false|false” custom_padding=”||||false|false” border_color_left=”rgba(0,0,0,0)” border_style_left=”none” locked=”off”]<\/p>\n\n
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1. Sending a notification email at the end of a user operation where other users are also involved<\/h2>\n
public<\/span> class<\/span> CommentService {<\/span>\n\u00a0\n\tpublic<\/span> void<\/span> saveComment(<\/span>String<\/span> id, CommentRequest comment)<\/span> {<\/span>\n\u00a0\n\t\tItem item =<\/span> itemService.getItem<\/span>(<\/span>id)<\/span>.orElseThrow<\/span>(<\/span>ItemNotFoundException::<\/span>new<\/span>)<\/span>;<\/span>\n\t\tUser userToNotify =<\/span> userService.get<\/span>(<\/span>item.getCreator<\/span>)<\/span>.orElseThrow<\/span>(<\/span>UserNotFoundException::<\/span>new<\/span>)<\/span>\n\u00a0\n\t\tcommentService.save<\/span>(<\/span>comment)<\/span>;<\/span>\n\t\tmailService.sendCommentSavedNotification<\/span>(<\/span>userToNotify, comment)<\/span>;<\/span>\n\t}<\/span>\n}<\/span>\n\u00a0\n\u00a0\npublic<\/span> class<\/span> EmailService {<\/span>\n\u00a0\n\t@Async\n\tpublic<\/span> void<\/span> sendCommentSavedNotification(<\/span>User userToNotify, Item item)<\/span> {<\/span>\n\u00a0\n\t\tMimeMessageHelper mimeMessage =<\/span> \/\/prepare your email content here<\/span>\n\t\tjavaMailSender.send<\/span>(<\/span>mimeMessage)<\/span>;<\/span>\n\t}<\/span>\n}<\/span><\/pre>\n@Configuration\n@EnableAsync\npublic<\/span> class<\/span> AsyncConfiguration implements<\/span> AsyncConfigurer {<\/span>\/\/no special body needed yet}<\/span><\/pre>\n2. Uploading multiple documents with the cancellation feature<\/h2>\n
public<\/span> class<\/span> DocumentController {<\/span>\n\u00a0\n\t@PostMapping(<\/span>\"\/files\"<\/span>)<\/span>\/\/start multiple upload, return processId right away<\/span>\n\tpublic<\/span> ResponseEntity<<\/span>ProcessIdResult><\/span> uploadDocuments(<\/span>@Valid @NotNull @RequestPart(<\/span>\"files\"<\/span>)<\/span> List<<\/span>MultipartFile><\/span> files,\n\t\t\t@RequestParam(<\/span>\"item\"<\/span>)<\/span> String<\/span> itemId)<\/span> {<\/span>\n\t\tString<\/span> processId =<\/span> ULID.nextUlid<\/span>(<\/span>)<\/span>;<\/span>\/\/generate random Id\n<\/span>\n\t\tdocumentService.upload<\/span>(<\/span>processId, itemId, files)<\/span>;<\/span> \/\/call async method\n<\/span>\n\t\treturn<\/span> new<\/span> ResponseEntity<><\/span>(<\/span>new<\/span> ProcessIdResult(<\/span>processId)<\/span>, HttpStatus.ACCEPTED<\/span>)<\/span>;<\/span>\n\t}<\/span>\n\u00a0\n\t@PostMapping(<\/span>\"\/cancel\"<\/span>)<\/span>\/\/cancel a specific process<\/span>\n\tResponseEntity<<\/span>ProcessIdResult><\/span> cancelUploadDocuments(<\/span>@RequestParam(<\/span>\"processId\"<\/span>)<\/span> String<\/span> processId)<\/span> {\n<\/span>\n\t\tdocumentService.cancel<\/span>(<\/span>processId)<\/span>;<\/span> \/\/send cancel event for this processId\n<\/span>\n\t\treturn<\/span> new<\/span> ResponseEntity<><\/span>(<\/span>HttpStatus.ACCEPTED<\/span>)<\/span>;<\/span>\n\t}<\/span>\n\u00a0\n\t@GetMapping(<\/span>\"\/status\"<\/span>)<\/span>\/\/get the status of a specific process<\/span>\n\tpublic<\/span> ResponseEntity<<\/span>ProcessIdStatus><\/span> getStatus(<\/span>@RequestParam(<\/span>\"processId\"<\/span>)<\/span> String<\/span> processId)<\/span> {\n<\/span>\n\t\tProcessIdStatus status =<\/span> documentService.getStatus<\/span>(<\/span>processId)<\/span>;<\/span> \/\/check status for this processId<\/span>\n\t\t\nreturn<\/span> new<\/span> ResponseEntity<><\/span>(<\/span>status, HttpStatus.OK<\/span>)<\/span>;<\/span>\n\t}<\/span>\n\u00a0\n}<\/span>\n\u00a0\n\u00a0\npublic<\/span> class<\/span> DocumentService {<\/span>\n\u00a0\n\tAsync\/\/using default Spring thread executor<\/span>\n\tpublic<\/span> void<\/span> upload(<\/span>String<\/span> processId, String<\/span> itemId, List<<\/span>MultipartFile><\/span> files)<\/span> {<\/span>\n\t\t\/\/send start event for this processId<\/span>\n\t\t\/\/start actual upload, checking after each document upload if cancel event was received<\/span>\n\t\t\/\/send finish\/cancel\/failed event for this processId at the end<\/span>\n\u00a0\n\t}<\/span>\n}<\/span><\/pre>\n\n
3. Complex backend calculations, requested by a user action<\/h2>\n
public<\/span> class<\/span> AuthorizationService {<\/span>\n\u00a0\n\tpublic<\/span> boolean<\/span> hasAccess(<\/span>User user, Item item)<\/span> {<\/span>\n\t\tList<<\/span>CompletableFuture<<\/span>Boolean>><\/span> parallelRequests =<\/span> new<\/span> ArrayList<><\/span>(<\/span>)<\/span>;<\/span>\n\t\tCompletableFuture<<\/span>Boolean><\/span> hasRightsInService1Future =<\/span> createFutureCallService1(<\/span>user, item)<\/span>;<\/span>\n\t\tCompletableFuture<<\/span>Boolean><\/span> hasRightsInService1Future =<\/span> createFutureCallService2(<\/span>user, item)<\/span>;<\/span>\n\u00a0\n\t\t\/\/run the http calls in parallel<\/span>\n\t\tCompletableFuture<<\/span>Void><\/span> combinedFuture =<\/span> CompletableFuture.allOf<\/span>(<\/span>parallelRequests.toArray<\/span>(<\/span>new<\/span> CompletableFuture[<\/span>]<\/span>{<\/span>}<\/span>)<\/span>