Csv API For Java

CSV API for Java

Apache Commons CSV

Check out Apache Common CSV.

This library reads and writes several variations of CSV, including the standard one RFC 4180. Also reads/writes Tab-delimited files.

• Excel
• InformixUnload
• InformixUnloadCsv
• MySQL
• Oracle
• PostgreSQLCsv
• PostgreSQLText
• RFC4180
• TDF

Import Response Data received from an API into CSV file

Solution:

• Step 1: Convert response to json in String format
• Step 2: Extract array data by Jackson, not Rest-Assured

String res = given()
                .get("https://gorest.co.in/public-api/users")
                .asString();
try {
     JsonNode jsonTree = new ObjectMapper().readTree(res).get("data");
     ...
}  

Design rule for responding to REST GET API with CSV output

My suggestions:

1. Keep the ResponseCSV immutable, no setters, provide constructor !

2. Change the CSVExportSvc.exportCSV signature to be easier, don't return boolean:

3. Try to set content type to csv/text.

The interface may be like this:

public interface CSVExportSvc {
   public ResponseCSV exportCSV(String sectionTypeName);
}

Java: download CSV file with REST service

Explainations:

You got inputStream first:

contentLengthOfStream =inputStreamResource.contentLength();

Then Spring's returnValueHandlers got inputStream again:

new ResponseEntity( inputStreamResource, httpHeaders, HttpStatus.OK ).

But the inputStream wrapped by inputStreamResource only can be used once:

/**
 * This implementation throws IllegalStateException if attempting to
 * read the underlying stream multiple times.
 */
public InputStream getInputStream() throws IOException, IllegalStateException {
    if (this.read) {
        throw new IllegalStateException("InputStream has already been read - " +
                "do not use InputStreamResource if a stream needs to be read multiple times");
    }
    this.read = true;
    return this.inputStream;
}

Solution: You can get bytes from inputStream and return the ResponseEntity with bytes.

@ApiOperation(value = "export",
        notes = "Export Cache details for a given criteria")
@ApiImplicitParams({

})
@ApiResponses(value = {
        @ApiResponse(code = 400, message = "Bad Request"),
        @ApiResponse(code = 404, message = "Not Found"),
        @ApiResponse(code = 500, message = "Internal Server Error") })
@RequestMapping(method = RequestMethod.GET, value = "/export")
public ResponseEntity export( HttpServletRequest request )
{
    CacheDataManager cacheResultHandler = new CacheDataManager();
    InputStreamResource inputStreamResource = null;
    InputStream inputStream = null;
    byte[] byteArray = new byte[0];
    HttpHeaders httpHeaders = new HttpHeaders();

    try
    {
        inputStreamResource = cacheResultHandler.exportCacheResults( request );
        httpHeaders.set( HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=" + "test.csv" );

        //convert inputStream to bytes
        inputStream = inputStreamResource.getInputStream();
        ByteArrayOutputStream buffer = new ByteArrayOutputStream();
        int nRead;
        byte[] data = new byte[1024];
        while ((nRead = inputStream.read(data, 0, data.length)) != -1) {
            buffer.write(data, 0, nRead);
        }

        buffer.flush();
        byteArray = buffer.toByteArray();

        httpHeaders.setContentLength(byteArray.length);
    }
    catch ( IOException e )
    {
        e.printStackTrace();
    }

    return new ResponseEntity( byteArray, httpHeaders, HttpStatus.OK );

}

Suggest: using Apache Commons IO to convert InputStream to bytes.Need to add a lib dependency,which can make your code brief

byte[] byteArray = IOUtils.toByteArray(inputStream);

Download CSV file via Rest

To force "save as", you need to set the content disposition HTTP header in the response. It should look like this:

Content-Disposition: attachment; filename="whatever.csv"

It looks like you're using JAX-RS. This question shows how to set the header. You can either write the CSV to the HTTP response stream and set the header there or return a Response object like so:

return Response.ok(myCsvText).header("Content-Disposition", "attachment; filename=" + fileName).build();

You do not need to write to a File object in the middle of this process so can avoid writing to disk.

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