A method created to store PDF files and CSV files in the BLOB type of Oracle. Until now, I have rarely dealt with byte arrays, so I will write it down so that I will not forget it in the future.

Operating environment

java Java SE 8u152

Method made

    public byte[] convertFile(File file) {
        try (FileInputStream inputStream = new FileInputStream(file);) {
            ByteArrayOutputStream bout = new ByteArrayOutputStream();
            byte[] buffer = new byte[1024];
            while(true) {
                int len = inputStream.read(buffer);
                if(len < 0) {
                    break;
                }
                bout.write(buffer, 0, len);
            }
            return bout.toByteArray();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

Modified version of the method I made

Based on what you told me in the comments, I will write some modified methods.

Method ①

A version that fixes the point that the infinite loop by while is not cool and forgetting to close ByteArrayoutputStream. The method described later is simpler, so if you have Java 7 or above, you should use method ② or later.

    public byte[] convertFile(File file) {
        File file = new File(dir + name);
        try (FileInputStream inputStream = new FileInputStream(file);
            ByteArrayOutputStream bout = new ByteArrayOutputStream();) {
           byte[] buffer = new byte[1024];
           int len = 0;
           while((len = inputStream.read(buffer)) != -1) {
               bout.write(buffer, 0, len);
           }
           return bout.toByteArray();
       } catch (Exception e) {
           e.printStackTrace();
       }
        return null;
    }

Method ②

How to use apache.commons.compress.utils.IOUtils.toByteArray. Any environment where you can add a library is OK.

    public byte[] convertFile(File file) throws IOException {
        FileInputStream inputStream = new FileInputStream(file);
        return IOUtils.toByteArray(inputStream);
    }

Method ③

How to use java.nio.file.Files.readAllBytes (). Note that it can only be used with Java 7 or above.

public byte[] convertFile(File file) throws IOException {
    return Files.readAllBytes(file.toPath());
}

Method ④

How to use java.io.InputStream.transferTo (). Note that it can only be used with Java 9 or above.

    public byte[] convertFile(File file) throws IOException {
        FileInputStream inputStream = new FileInputStream(file);
        return inputStream.transferTo(outputStream);
    }

Miscellaneous feelings

--This time it's Java 8, so using java.nio.file.Files.readAllBytes () may be the simplest with the fewest lines. --Failed to run into the method of using OutputStream and InputStream. I should have investigated more before implementing it ...

How to convert a file to a byte array in Java