How do I read and convert an InputStream object to string type?

0 votes

If you have java.io.InputStream object, how should you process that object and produce a String?


Suppose I have an InputStream that contains text data, and I want to convert this to a String. For example, so I can write the contents of the stream to a log file.

What is the easiest way to take the InputStream and convert it to a String?

public String convertStreamToString(InputStream is) { 
    // ???
}
Apr 17, 2018 in Java by parth295
• 4,620 points
3,294 views

2 answers to this question.

0 votes

Ways to convert an InputStream to a String:

  1. Using IOUtils.toString (Apache Utils)

    String result = IOUtils.toString(inputStream, StandardCharsets.UTF_8);
  2. Using CharStreams (guava)

    String result = CharStreams.toString(new InputStreamReader(
          inputStream, Charsets.UTF_8));
  3. Using Scanner (JDK)

    Scanner s = new Scanner(inputStream).useDelimiter("\\A");
    String result = s.hasNext() ? s.next() : "";
  4. Using Stream Api (Java 8). Warning: This solution convert different line breaks (like \r\n) to \n.

    String result = new BufferedReader(new InputStreamReader(inputStream))
      .lines().collect(Collectors.joining("\n"));
  5. Using parallel Stream Api (Java 8). Warning: This solution convert different line breaks (like \r\n) to \n.

    String result = new BufferedReader(new InputStreamReader(inputStream)).lines()
       .parallel().collect(Collectors.joining("\n"));
  6. Using InputStreamReader and StringBuilder (JDK)

    final int bufferSize = 1024;
    final char[] buffer = new char[bufferSize];
    final StringBuilder out = new StringBuilder();
    Reader in = new InputStreamReader(inputStream, "UTF-8");
    for (; ; ) {
        int rsz = in.read(buffer, 0, buffer.length);
        if (rsz < 0)
            break;
        out.append(buffer, 0, rsz);
    }
    return out.toString();
  7. Using StringWriter and IOUtils.copy (Apache Commons)

    StringWriter writer = new StringWriter();
    IOUtils.copy(inputStream, writer, "UTF-8");
    return writer.toString();
  8. Using ByteArrayOutputStream and inputStream.read (JDK)

    ByteArrayOutputStream result = new ByteArrayOutputStream();
    byte[] buffer = new byte[1024];
    int length;
    while ((length = inputStream.read(buffer)) != -1) {
        result.write(buffer, 0, length);
    }
    // StandardCharsets.UTF_8.name() > JDK 7
    return result.toString("UTF-8");
  9. Using BufferedReader (JDK). Warning: This solution convert different line breaks (like \n\r) to line.separator system property (for example, in Windows to "\r\n").

    String newLine = System.getProperty("line.separator");
    BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));
    StringBuilder result = new StringBuilder();
    String line; boolean flag = false;
    while ((line = reader.readLine()) != null) {
        result.append(flag? newLine: "").append(line);
        flag = true;
    }
    return result.toString();
  10. Using BufferedInputStream and ByteArrayOutputStream (JDK)

    BufferedInputStream bis = new BufferedInputStream(inputStream);
    ByteArrayOutputStream buf = new ByteArrayOutputStream();
    int result = bis.read();
    while(result != -1) {
        buf.write((byte) result);
        result = bis.read();
    }
    // StandardCharsets.UTF_8.name() > JDK 7
    return buf.toString("UTF-8");
  11. Using inputStream.read() and StringBuilder (JDK). Warning: This solution has problem with Unicode, for example with Russian text (work correctly only with non-Unicode text)

    int ch;
    StringBuilder sb = new StringBuilder();
    while((ch = inputStream.read()) != -1)
        sb.append((char)ch);
    reset();
    return sb.toString();

Warning:

  1. Solutions 4, 5 and 9 convert different line breaks to one.

  2. Solution 11 can't work correctly with Unicode text

answered Apr 17, 2018 by Rishabh
• 3,540 points
0 votes

You can also use Java Standard Library to read and convert object into String type.

static String convertStreamToString(java.io.InputStream is) {
    java.util.Scanner s = new java.util.Scanner(is).useDelimiter("\\A");
    return s.hasNext() ? s.next() : "";
}
answered Jul 17, 2018 by Sushmita
• 6,880 points

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