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

Question

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

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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) { 
    // ???
}

Answer 1

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

Answer 2

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() : "";
}