Handles how to load static or dynamic resource in Spring jar: ClassPathResource, ResourceLoader.


Index

  1. How to load static/dynamic resource in Spring jar
  2. Fun fact

How to load static/dynamic resource in Spring jar

First case: Static resource

Roughly 4 months age, I was assigned to make function with excel. It was like this. I had made a template excel in advance and my colleagues downloaded it and filled it. After that, I read it and inserted data to database.

Point of static resource

  • I have to make and save file before deploying. (making jar file)
  • Never got changed, because it’s a template!
  • Can saved in jar static dir (inside of jar)

Second case: Dynamic resource

And this week, I was assigned new function also related with excel. I have to make a excel file which is analysis purpose and let it get downloaded. Sadly, data in the excel file get changed frequently. This function has to make excel every request.

Point of dynamic resource

  • I have to make and save file on run time.
  • Always freshly made!
  • jar already closed, can saved in other dir (outside of jar)

Both are about downloading excel file in server. But there is a huge difference.


How to load then?

  1. Use ClassPathResource and relative path to get file static resource in jar
  2. Use ResourceLoader and absolute path to get file dynamic resource outside of jar

Take a look at [Classpath resource not found when running as jar].


ClassPathResource for static resource

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private final MediaType excelType = MediaType.parseMediaType("application/vnd.ms-excel");

String EXCEL_STATIC_PATH = "static/excel/"

@GetMapping("/{data}/template/download")
@ResponseBody
public ResponseEntity<Resource> getTemplate(
    @PathVariable(name = "data") String data
) {
    String requestData = Util.nvl(data);
    String fileName = "";

    if (requestData.equals("vts")) {
        fileName = "vts_template.xlsx"; 
    }

    try {
        ClassPathResource classPathResource = new ClassPathResource(EXCEL_STATIC_PATH + fileName);

        return ResponseEntity.ok()
            .header(HttpHeaders.CONTENT_DISPOSITION, "attachment;filename=" + classPathResource.getFilename())
            .header(HttpHeaders.CONTENT_LENGTH, String.valueOf(classPathResource.contentLength()))
            .header(HttpHeaders.CONTENT_TYPE, String.valueOf(excelType))
            .body(classPathResource);

    } catch (Exception e) {
        log.error(e.getMessage(), e);
        return ResponseEntity.status(HttpStatus.INTERNAL_SERVER_ERROR).build();
    }
}

ResourceLoader for dynamic resource

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@Autowired
private ResourceLoader resourceLoader;
      
@Value("${property.excel.dir}")
private String EXCEL_GENERATED_DIR; 

@GetMapping(value = "/{type}/count/download")
@ResponseBody
public ResponseEntity<Resource> testGetValueFromExcel(
    @PathVariable(name = "type") String type
) {
    
    String ttsType = validDnxTts.get(type);

    String fileName = excelService.makeVtsMessageExcel(ttsType, type, EXCEL_GENERATED_DIR);
    Resource resultResource;
    
    try {
        // This name will be showed up to client
        String fullFile = new StringBuilder().append(EXCEL_SEVER_HOST).append("_").append(fileName).toString();
    
        resultResource = resourceLoader.getResource("file:" + EXCEL_GENERATED_DIR + fileName);
    
        return ResponseEntity.ok()
            .header(HttpHeaders.CONTENT_DISPOSITION, "attachment;filename=" + fullFile)
            .header(HttpHeaders.CONTENT_LENGTH, String.valueOf(resultResource.contentLength()))
            .header(HttpHeaders.CONTENT_TYPE, String.valueOf(excelType))
            .body(resultResource);

    } catch (Exception e) {
        log.error(e.getMessage(), e);
        return ResponseEntity.status(HttpStatus.INTERNAL_SERVER_ERROR).build();
    }
}

Fun fact

File Path in Windows and Linux

File storage path grammar is different, so had better write down both on properties file.


Windows file path

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property.excel.dir=\\C:\\Temp\\Admin\\

Linux file path

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property.excel.dir=/opt/temp/

Accident with /

I accidentally attached / in resourceLoader.getResource(“file:” + EXCEL_GENERATED_DIR + fileName);

So in Linux, it looks like file://opt/temp/. In this case, I saw java.net.UnknownHostException: socialweb-analytics.lcloud.com: Name or service not known exception lol. Server thinks it’s host.