How to Return CSV Data in Browser From Spring Controller

Question

Let say I have CSV data in a string and want to return it from a Spring controller. Imagine the data looks like this

a,b,c 
1,2,3
4,5,6

No matter what I have tried, the newlines come out as literally '\n' in the response content, and if I double escape them as in "\n", the response just contains the double backslashes too. In general, how to I return plain text data with newlines in it without the newlines being modified? I know how to return plain text, but still, the content comes with escaped newlines... This is what I current have (using Spring 3.0.5, not by choice)

@RequestMapping(value = "/api/foo.csv")
public ResponseEntity<String> fooAsCSV() {

    HttpHeaders responseHeaders = new HttpHeaders();
    responseHeaders.add("Content-Type", "text/plain; charset=utf-8");

    String data = "a,b,c\n1,2,3\n3,4,5";
    return new ResponseEntity<>(data, responseHeaders, HttpStatus.OK);
}

Which produces literally the string

"a,b,c\n1,2,3\n,3,4,5"

In the browser. How do I make it produce the correct data with new lines in tact as shown above?

Solution 1

You could write to the response directly using e.g.

@RequestMapping(value = "/api/foo.csv")
public void fooAsCSV(HttpServletResponse response) {         
    response.setContentType("text/plain; charset=utf-8");
    response.getWriter().print("a,b,c\n1,2,3\n3,4,5");
}

Since the return type is void and HttpServletResponse is declared as a method argument the request is assumed to be completed when this method returns.

Solution 2

You can use the library supercsv.

<dependency>
  <groupId>net.sf.supercsv</groupId>
  <artifactId>super-csv</artifactId>
  <version>2.1.0</version>
</dependency>

Here is how to use it:

1- define your model class that you want to write as csv:

public class Book {
private String title;
private String description;
private String author;
private String publisher;
private String isbn;
private String publishedDate;
private float price;

public Book() {
}

public Book(String title, String description, String author, String publisher,
        String isbn, String publishedDate, float price) {
    this.title = title;
    this.description = description;
    this.author = author;
    this.publisher = publisher;
    this.isbn = isbn;
    this.publishedDate = publishedDate;
    this.price = price;
}

// getters and setters...
}

2- Do the following magic:

import java.io.IOException;
import java.util.Arrays;
import java.util.List;

import javax.servlet.http.HttpServletResponse;


import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.supercsv.io.CsvBeanWriter;
import org.supercsv.io.ICsvBeanWriter;
import org.supercsv.prefs.CsvPreference;

/**
 * This Spring controller class implements a CSV file download functionality.
 *
 */
@Controller
public class CSVFileDownloadController {
    @RequestMapping(value = "/downloadCSV")
    public void downloadCSV(HttpServletResponse response) throws IOException {

        String csvFileName = "books.csv";

        response.setContentType("text/csv");

        // creates mock data
        String headerKey = "Content-Disposition";
        String headerValue = String.format("attachment; filename=\"%s\"",
            csvFileName);
        response.setHeader(headerKey, headerValue);

        Book book1 = new Book("Effective Java", "Java Best Practices",
            "Joshua Bloch", "Addision-Wesley", "0321356683", "05/08/2008",
            38);

        Book book2 = new Book("Head First Java", "Java for Beginners",
            "Kathy Sierra & Bert Bates", "O'Reilly Media", "0321356683",
            "02/09/2005", 30);

        Book book3 = new Book("Thinking in Java", "Java Core In-depth",
            "Bruce Eckel", "Prentice Hall", "0131872486", "02/26/2006", 45);

        Book book4 = new Book("Java Generics and Collections",
            "Comprehensive guide to generics and collections",
            "Naftalin & Philip Wadler", "O'Reilly Media", "0596527756",
            "10/24/2006", 27);

        List<Book> listBooks = Arrays.asList(book1, book2, book3, book4);

        // uses the Super CSV API to generate CSV data from the model data
        ICsvBeanWriter csvWriter = new CsvBeanWriter(response.getWriter(),
            CsvPreference.STANDARD_PREFERENCE);

        String[] header = { "Title", "Description", "Author", "Publisher",
            "isbn", "PublishedDate", "Price" };

        csvWriter.writeHeader(header);

        for (Book aBook : listBooks) {
            csvWriter.write(aBook, header);
        }

        csvWriter.close();
    }
}

Solution 3

Have you tried @ResponseBody on your controller method?

@RequestMapping(value = "/api/foo.csv")
@ResponseBody
public String fooAsCSV(HttpServletResponse response) {         
    response.setContentType("text/plain; charset=utf-8");
    String data = "a,b,c\n1,2,3\n3,4,5";
    return data;
}

Edit: Spring docs explain it here: http://docs.spring.io/spring/docs/3.0.x/spring-framework-reference/html/mvc.html#mvc-ann-responsebody

Solution 4

here is a more detailed example for Bart's answer:

@GetMapping(value = "csv")
public void exportCsv(HttpServletResponse response) {
    try {
        // prepare response encoding and Headers
        response.setContentType("text/csv");
        response.setCharacterEncoding(StandardCharsets.UTF_8.name());
        response.setHeader("Content-Disposition", "attachment; filename=a.csv"); // specify the real file name users will get when download
        try (Writer writer = new OutputStreamWriter(response.getOutputStream(), StandardCharsets.UTF_8)) {
            // writer.write('\uFEFF'); // BOM is essential in some scenary
            writer.write("key,value\n");
            List<Row> row = rowService.getAll();
            for (Column column : row) {
                writer.write(String.format("%d,%s)\n",column.getKey(), column.getValue()));
            }
            writer.flush(); // DONNOT forget to flush writer after everything done
        } // writer will be closed automatically
    } catch (IOException e) {
        log.error("failed to export csv", e);
    }
}

Solution 5

I had a similar task lately. Used ResponseEntity<byte[]> and the response header Content-Disposition. Like this:

@RequestMapping(value = "/api/foo.csv")
public ResponseEntity<byte[]> fooAsCSV() {

  HttpHeaders responseHeaders = new HttpHeaders();
  responseHeaders.add("Content-Type", "application/vnd.ms-excel");
  responseHeaders.add("Content-Disposition", "attachment; filename=abc.csv");

  String data = "a,b,c\n1,2,3\n3,4,5";
  return new ResponseEntity<>(data.getBytes("ISO8859-15"), responseHeaders, HttpStatus.OK);
}

View more solutions

Comments

[Marcel Stör]

What if your method signature says public String fooAsCSV() with @RequestMapping(value = "/api/foo.csv", method = RequestMethod.GET, produces="text/plain") and then return "a,b,c\n1,2,3\n,3,4,5"; i.e. returning a string directly instead of using ResponseEntity

[David Williams]

Unfortunately that is only available in Spring 3.1+

[Marcel Stör]

Ouch, missed the "Spring 3.0.5" bit, sorry.

[David Williams]

Hey no worries, thanks for reading and taking the time. Still not sure how to do this, I found a slightly hacky way which is to set the content type to text/html and put <br/> instead of \n. That makes me feel dirty.

[Bart]

Maybe you can try to write a trivial message converter yourself. I'm not sure where the problem lies but I bet you could try and steal the StringHttpMessageConverter from another version of Spring and see what happens. I tested your method in Spring 4 and it works like expected.

[Alex R]

Possible duplicate of How to make "Save As" window pop up when downloading files in Spring MVC?

[David Williams]

I did add the @ResponseBody annotation, but hey, writing to the output stream directly might do the trick. Let me try that.

[Bart]

I was commenting to @nickdos his answer and it came to me. Always funny to realize how simple the solution is.

[nickdos]

copy and paste error - return type now String. See docs.spring.io/spring/docs/3.0.x/spring-framework-reference/‌​…

[David Williams]

Totally, I'm not sure if I was tired or what but this should have been way more obvious :)