How to temporarily create a text file without any file location and send as a response in spring boo-CodePudding

Need to create a txt file by the available data and then need to send the file as rest response. the app is deployed in container. i dont want to store it in any location on container or any location in spring boot resources. is there any way where we can create file at runtime buffer without giving any file location and then send it in rest response? App is production app so i need a solution which is secure

CodePudding user response：

A file is a file. You're using the wrong words - in java, the concept of a stream of data, at least for this kind of job, is called an InputStream or an OutputStream.

Whatever method you have that takes a File? That's the end of the road. A File is a file. You can't fake it. But, talk to the developers, or check for alternate methods, because there is absolutely no reason anything in java that does data processing requires a File. It should be requiring an InputStream or possibly a Reader. Or perhaps even there is a method that gives you an OutputStream or Writer. All of these things are fine - they are abstractions that lets you just send data to it, from a file, a network connection, or made up whole cloth, which is what you want.

Once you have one of those, it's trivial. For example:

String text = "The Text you wanted to store in a fake file";
byte[] data = text.getBytes(StandardCharsets.UTF_8);
ByteArrayInputStream in = new ByteArrayInputStream(data);
whateverSystemYouNeedToSendThisTo.send(in);

Or for example:

String text = "The Text you wanted to store in a fake file";
byte[] data = text.getBytes(StandardCharsets.UTF_8);
try (var out = whateverSystemYouNeedToSendThisTo.getOUtputStream()) {
  out.write(data);
}

CodePudding user response：

Take a look at the function below:

Imports

import com.google.common.io.Files;
import org.springframework.http.ContentDisposition;
import org.springframework.http.HttpHeaders;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.GetMapping;
import java.io.*;
import java.nio.file.Paths;

Function:

@GetMapping(value = "/getFile", produces = MediaType.APPLICATION_OCTET_STREAM_VALUE)
    private ResponseEntity<byte[]> getFile() throws IOException {
        File tempDir = Files.createTempDir();
        File file = Paths.get(tempDir.getAbsolutePath(), "fileName.txt").toFile();
        String data = "Some data"; //
        try (FileWriter fileWriter = new FileWriter(file)) {
            fileWriter.append(data).flush();
        } catch (Exception ex) {
            ex.printStackTrace();
        }
        byte[] zippedData = toByteArray(new FileInputStream(file));
        HttpHeaders httpHeaders = new HttpHeaders();
        httpHeaders.setContentDisposition(ContentDisposition.builder("attachment").filename("file.txt").build());
        httpHeaders.setContentType(MediaType.APPLICATION_OCTET_STREAM);
        httpHeaders.setContentLength(zippedData.length);
        return ResponseEntity.ok().headers(httpHeaders).body(zippedData);
    }

    public static byte[] toByteArray(InputStream in) throws IOException {
        ByteArrayOutputStream os = new ByteArrayOutputStream();
        byte[] buffer = new byte[in.available()];
        int len;
        // read bytes from the input stream and store them in buffer
        while ((len = in.read(buffer)) != -1) {
            // write bytes from the buffer into output stream
            os.write(buffer, 0, len);
        }
        return os.toByteArray();
    }