How to stream large csv in Spring4 rest api?

Question

I am using spring 4 web-mvc to create a rest api. I have a gigantic csv file that I want to stream. In python I can do very simple:

from flask import Response

@app.route('/large.csv')
def generate_large_csv():
    def generate():
        for row in iter_all_rows():
            yield ','.join(row) + '\n'
    return Response(generate(), mimetype='text/csv')

What is the equivalent in Spring 4? Is this possible?

Wenbing Li · Accepted Answer · 2015-04-10 03:19:36Z

3

Below is pseudo code as a hint for you:

@RequestMapping(value = "/large.csv", method = GET, produces = "text/csv")
@ResponseStatus(value = HttpStatus.OK)
public void streamLargeCSV(OutputStream output) {
    InputStream is = new FileInputStream(csvFile);
    int read=0;
    byte[] bytes = new byte[1024 * 4];  //size per read

    while((read = is.read(bytes))!= -1){
        output.write(bytes, 0, read);
        output.flush();  //may change flush rate to more rows/flush
    }
    output.close()
}

edited Apr 10, 2015 at 3:19

answered Apr 10, 2015 at 3:12

Wenbing Li

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4 Comments

Rolando Over a year ago

My csv is 16GB, my memory is 4GB. My memory will not crash from this right?

Wenbing Li Over a year ago

Basically you need to read your file as streaming as well. Let me update my answer to read from file.

Rolando Over a year ago

In spring usually I return something like a String or something, but in your code you use a "void", would it actually return to the browser without using any return statement?

Wenbing Li Over a year ago

As for this one, we inject OutputStream output. Therefore, no return value required.

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