Return file in an object from spring rest controller

Question

I am trying to create a rest controller which returns an object which contains a String, Long and a csv file. I am unable to do it because as soon I write the file creation logic in java, rather than returning it, it creates a file on my host.

I have already tried to write the entire object to the httpservletresponse using writer and output stream, but it did not give the expected result. I returned the object from controller, but instead of returning the object, it created a file on my host and did not return other values at all.

public class MyReturnObject {
  private Long countOfRows;

  private File csvDataFile;

  private String errorMessage;
}

@RequestMapping(value = "/api/fetchInfo", method = RequestMethod.GET)
public MyReturnObject fetchInfoRestControllerMethod (String param1) {
//some logic/ service calls
return createMyReturnObject(values);
}

public MyReturnObject createMyReturnObject(List<CustomObject> values) {
  File csvFile = new File("myinfo.csv");
  file.createNewFile();
  FileWriter writer = new FileWriter(csvFile);
  writer.write("test");
  //some lines
  MyReturnObject returnObject = MyReturnObject.builder()
                                .countOfRows(x)
                                .csvDataFile(csvFile)
                                .errorMessage(y).build();

  return returnObject;

}

This is just some dummy code I wrote. The object that I am building in createMyReturnObject is not returning the expected result. I am thinking if it is possible to return something like object MyReturnObject from a rest controller. Please help me with ideas to get expected results.

score 1 · Answer 1 · answered Sep 20 '19 at 21:21

1

Unfortunately, you cannot have two response bodies at the same time. You can have it either set to text/csv or to text/json and you can return a single response body at a time.

However, you can convert your CSV into bytes and Base64.enocode it and put inside of the object. You can also store your CSV in a string and return it with a custom line separator.

answered Sep 20 '19 at 21:21

Alan Sereb

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I do not have a CSV already available, I need to create it in the code so I believe `Base64.encode` will not be the appropriate way to do it. Any idea how the string can be interpreted as csv file by the caller method which is java fetch call? – Madhu Priya Sep 21 '19 at 05:22
Okay, if you can't to make your file downloadable and return it as a json. However, you can return json object with csv inside one of the properties and on the frontend parse that property, create csv and send it to a client. [This](https://stackoverflow.com/a/9834261/6252399) is one of the examples – Alan Sereb Sep 21 '19 at 13:34

score 0 · Answer 2 · answered Sep 20 '19 at 21:55

Serialize your class MyReturnObject use a jackson library or gson in you project.

@RequestMapping(value = "/api/fetchInfo", method = RequestMethod.GET)
public @ResponseBody MyReturnObject fetchInfoRestControllerMethod (String param1) {
    return MyReturnObject.builder()
                                .countOfRows(x)
                                .csvDataFile(csvFile)
                                .errorMessage(y).build();
}

Sorry, I am unable to understand how can I retain csv file after the serialization of object and how can file be serialized. — Madhu Priya, Sep 21 '19 at 05:29

Return file in an object from spring rest controller

2 Answers2