Practice of online problem feedback module (11): realize image download function

author ：bug bacteria

️ Blog ：CSDN、 Nuggets etc.

official account ： Ape circle wonderful house

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【 Developing the cloud 】 It's a discount every year , You don't have to go around collecting sheep

One 、 Preface

        The next few issues ,bug I want to share with you that I just received a temporary demand yesterday , It's hot , I would like to share how I faced the temporary requirements and made the whole development cycle , It includes sorting out businesses, creating business tables, realizing business logic to form a closed loop, and connecting with the front end , Some business development and functional development will be interspersed , This one-stop process is witnessed online with you , Share with the novice , I hope it will help you .

Environmental statement ：idea2019.3 + springboot2.3.1.REALSE + mybati-plus3.2.0 + mysql5.6 + jdk1.8

        If the partners feel that the article is helpful to you in the process of reviewing the article , Please don't be stingy with your praise , Boldly put the article Lighten up Well , Your likes are three in a row ( Collection ️+ Focus on + Leaving a message. ) That's right bug The best encouragement and support on my creative path . Time does not give up ‍*️, Create constantly , come on. ️ 

Two 、 Text

        This issue , I then focus on the picture , Since we want to teach , It is necessary to complete the addition, deletion, modification and check of the pictures . So for you in the future , If there is any business related to pictures , Then you have no pressure , Follow my tutorial directly , I'll teach you hand in hand , This must be the fastest and best zero foundation introductory teaching , Maybe they will be appreciated by the leaders , Work , It's not just about code safety and efficiency , Get off work early , Try to finish the workload of the day within working hours , This is the goal of everyone , It's yours and mine .

        Let's not talk more nonsense , Start today's content directly .

3、 ... and 、 How to code image download

        Our content today is to download pictures , Since the business supports image uploading , Then you must support local downloading of images , So how to download images from the server to the local ？ This is obviously a problem ？ But today I , From zero to zero, I will lead you to complete analysis, implementation, and testing , One stop service to arrange you all properly .

1️⃣ Definition Controller request

        Let's define the interface request first , So let's analyze that , Since the picture is to be downloaded , You must find the full path of the image , So for this business interface , The input parameter definitely needs two parameters , Enter the reference 1 The full name of the picture , for example test.jpg, Enter the reference 2 Domain account id, Because if you want to splice the full path of the image resource address , This must be based on the domain account id To be spliced as sub paths , This is also related to the business definition , You can also not distinguish people , Just put all the picture resources in a large resource pool , I just need to upload people into folders , To need someone to upload the saved domain account id As a precondition .

        Now that the analysis is finished, enter the parameters , Then the interface definition will have an outline , Let's see . For reference only ：

    @GetMapping("/download-img-by-path")
    @ApiOperation(value = " Images are downloaded ", notes = " Download pictures according to the picture address ")
    public void downloadImgByPath(@ApiParam(" Picture path ") @RequestParam("imgPath") String imgPath,
                                  @ApiParam(" Domain account number of the feedback person id") @RequestParam("accountId") String accountId) throws IOException {
        userQuestionsService.downloadImgByPath(imgPath, accountId);
    }

          It should be noted that , Your interface request path , It's best to know what you mean by what you see , It is also convenient to debug and distinguish interface requests on the page in the future .

2️⃣ Definition downloadImgByPath() Interface

        Then we're going to service The interface layer defines the downloadImgByPath() The method .

    void downloadImgByPath(String imgPath, String accountId) throws IOException;

3️⃣ Realization downloadImgByPath() Method

        Next is the core of the interface , But here , In order to avoid code redundancy in the future , Here we still encapsulate the image download method into a public method , So for some pictures to download ,pdf Download and other files , Just call it directly , Let's package , The most important thing is the resource saving path , therefore , If you want to join us, just give us a break , Download resources according to the resource path .

The specific code implementation is as follows ：

    @Override
    public void downloadImgByPath(String imgPath, String accountId) throws IOException {

        // Full path of stitching preview picture 
        String targetPath = this.buildImgPath(imgPath, accountId);
        // Call the download method 
        uploader.downloadImg(targetPath);
    }

        For the image path splicing method , It depends on your actual business , Just splice all the saved paths of the resource . Then I also encapsulated the core method of the image into uploader It's in the actuator , It involves public methods such as uploading and downloading resources . 

4️⃣ Realize the picture downloadImg() Download method

         How to download image resources , This requires the help of a tool ,IOUtils Tool class , It has a method that provides a stream assignment copyLarge(), You can look at its source code , Interested friends can think about it .

public static long copyLarge(InputStream input, OutputStream output) throws IOException {
        return copy(input, output, 4096);
}

        and  copyLarge() Method is also an important step to download image resources , How to use it in combination , Please have a look at bug The core method of bacteria writing , For reference only .

    /**
     *  Images are downloaded 
     */
    public void downloadImg(String targetPath) {

        FileInputStream inputStream = null;

        HttpServletResponse response = SpringServletContextUtils.getResponse();
        try {

            // Set file header , The last parameter is to set the download file name 
            response.setHeader("Content-Disposition", "attachment;fileName=" + FilenameUtils.getName(targetPath));

            File file = new File(targetPath);
            inputStream = new FileInputStream(file);
            OutputStream outputStream = response.getOutputStream();
            IOUtils.copyLarge(inputStream, outputStream);

            outputStream.flush();
        } catch (IOException e) {
            log.error(e.getMessage(), e);
        } finally {
            // Shut off flow 
            IOUtils.closeQuietly(inputStream);
        }
    }

        This method is very brief , The only thing to be exposed is the full path of resources , This has to be determined by the caller , If the resource does not exist , It must fail to download . 

5️⃣ The interface test

        Then we will test the image download , This also involves a very important link , If you are an interface not added to the white list , That must involve token Login authentication , So for safety's sake , I set the interface call to not block the whitelist , That is, I can directly request the address through the browser to download the image resources .

        Or you can use postman Interface debugging , It also supports the image download function , I will demonstrate it to you below .

Mode one ： Browser test image download

        First of all, you should ensure that the image resource exists , So here I am , I am making sure that the picture exists , Let me show you .

        You must ensure that you can find resources for the full path of the picture , Otherwise, it must be a blank picture . As shown in the figure below :

        And the correct address , Download the picture , open , To be exact, it must be the picture you specified to download .

  Mode two ：postman Test image download  

        choice send You can preview the picture directly , But what we want is to save the image from the server to the local , That is, we pull down 【Send】 choice 【Send and download】 Option will jump to open a locally saved window , I will choose to save to the desktop .

         I saved it directly to the desktop , You can see that , The default file name will be changed to response, It is not downloaded and saved according to its original name, but downloading through the browser will not cause such problems .

6️⃣ summary

        Relatively speaking , It's still one step , Nothing happened bug, This measurement function is available , You can rest assured copy Ha .

 ... ...

        All right. , The above is all about this issue , Have you learned to give up ？ If it helps you , Please don't forget to give bug bacteria [ Three companies support ] yo . If you want to get more learning resources or want to communicate with more technology enthusiasts , You can pay attention to my official account. 『 Ape circle wonderful house 』, The backstage replies the key words to get the learning materials 、 Big factory surface 、 Interview templates and other massive resources , Just wait for you to get .

Four 、 I recommend

        For the actual development of the problem feedback module , I combed the teaching and link address of each issue completely , For reference only ： I hope it can help you .

• Practice of online problem feedback module ( One ): Sort out business requirements and create database tables
• Practice of online problem feedback module ( Two ): Encapsulate code to automatically generate class file
• Practice of online problem feedback module ( 3、 ... and ): Automatically generate all Controller、Service、Mapper Wait for the documents
• Practice of online problem feedback module ( Four ): Encapsulate generic field classes
• Practice of online problem feedback module ( 5、 ... and ): Realize the automatic filling function of general field content
• Practice of online problem feedback module ( 6、 ... and ): Interface document definition
• Practice of online problem feedback module ( 7、 ... and ): Installation and deployment swagger2
• ​ Practice of online problem feedback module ( 8、 ... and )​: Realize image upload function ( On )
• ​ Practice of online problem feedback module ( Nine )​: Realize image upload function ( Next )
• ​ Practice of online problem feedback module ( Ten )​: Realize the picture preview function
• ​ Practice of online problem feedback module ( 11、 ... and )​: Realize the picture download function
• ​ Practice of online problem feedback module ( Twelve )​: Realize the function of deleting pictures
• ​ Practice of online problem feedback module ( 13、 ... and )​: Realize multi parameter paging query list
• Practice of online problem feedback module ( fourteen ): Realize the online question answering function
• Practice of online problem feedback module ( 15、 ... and )​: Realize the function of online updating feedback status
• Practice of online problem feedback module ( sixteen )​: Realize the function of checking details
• Practice of online problem feedback module ( seventeen ): Realization excel Template online download function
• Practice of online problem feedback module ( eighteen ): Realization excel Batch import function of account file records
• Practice of online problem feedback module ( nineteen ): Realize batch export of data to excel Function in file
• Practice of online problem feedback module ( twenty ): Conclusion

        The above is the content of 20 issues , Each issue is dry , For the development of a module , How to build and test the deployment online bit by bit , I'll say it again , This is not an exercise , It's actual combat ！ It's actual combat ！ It's actual combat ！

         If you think you just need to understand one of the knowledge points or business , No objection , Just choose a few of them to study , It's all over anyway ; I just hope you can gain something , Grow up , It's not in vain for me to summarize and update you after work every day .

5、 ... and 、 At the end of the article

         If you want to learn more , Little friends can pay attention to bug I created a special column for you 《springboot Zero basic introductory teaching 》, It's all my hands , Ongoing update , I hope I can help more friends .

【 Developing the cloud 】 It's a discount every year , You don't have to go around collecting sheep

        I am a bug bacteria , A procedural ape who wants to get out of the mountain and change his fate . There's a long way to go , Are waiting for us to break through 、 To challenge . Come on , friends , Let's cheer together ！ The future can be expected ,fighting！

         Finally, I'll give you two words I like very much , Share with you ！

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️ Be what you want to be , No time limit , As long as willing , Anytime? start.

You can change... From now on , It can be the same , This matter , There are no rules , You can live your best .

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