How to convert InputStream to String in Java

This article shows a few ways to convert an java.io.InputStream to a String.

Table of contents

• 1. ByteArrayOutputStream
• 2. InputStream#readAllBytes (Java 9)
• 3. InputStreamReader + StringBuilder
• 4. InputStreamReader + BufferedReader (modified line breaks)
• 5. Java 8 BufferedReader#lines (modified line breaks)
• 6. Apache Commons IO
• 7. Download Source Code
• 8. References

1. ByteArrayOutputStream

This example opens a website google.com as an InputStream, and we use ByteArrayOutputStream to convert the InputStream to a String and print it out.

package com.mkyong.string;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.URI;

public class ConvertInputStreamToString {

    public static final int DEFAULT_BUFFER_SIZE = 8192;

    public static void main(String[] args) throws IOException {

        URI uri = URI.create("https://www.google.com/");
        try (InputStream inputStream = uri.toURL().openStream()) {

            // Convert InputStream -> String
            String result = convertInputStreamToString(inputStream);

            System.out.println(result);

        }

    }

    // Plain Java
    private static String convertInputStreamToString(InputStream is) throws IOException {

        ByteArrayOutputStream result = new ByteArrayOutputStream();
        byte[] buffer = new byte[DEFAULT_BUFFER_SIZE];
        int length;
        while ((length = is.read(buffer)) != -1) {
            result.write(buffer, 0, length);
        }

        // Java 1.1
        //return result.toString(StandardCharsets.UTF_8.name());

        return result.toString("UTF-8");

        // Java 10
        //return result.toString(StandardCharsets.UTF_8);

    }

}

2. InputStream#readAllBytes (Java 9)

2.1 In Java 9, we can use the new InputStream#readAllBytes() API to convert the input stream to bytes, later we use the new String() to create a new String object.

// @Java 9 -> inputStream.readAllBytes()
// max bytes Integer.MAX_VALUE, 2147483647, which is 2G
private static String convertInputStreamToString(InputStream inputStream)
        throws IOException {

    return new String(inputStream.readAllBytes(), StandardCharsets.UTF_8);
}

2.2 Review the InputStream source code; it reads all bytes into a byte array, which has a limit of Integer.MAX_VALUE or 2G; Since then, it is not intended for reading input streams with large amounts of data.

package java.io;

public abstract class InputStream implements Closeable {

  public byte[] readAllBytes() throws IOException {
  		return readNBytes(Integer.MAX_VALUE);
  }

  //...
}

3. InputStreamReader + StringBuilder

The Reader read a char at a time, slow.

// InputStreamReader + StringBuilder
private static String convertInputStreamToString(InputStream inputStream)
        throws IOException {

    final char[] buffer = new char[8192];
    final StringBuilder result = new StringBuilder();

    // InputStream -> Reader
    try (Reader reader = new InputStreamReader(inputStream, StandardCharsets.UTF_8)) {
        int charsRead;
        while ((charsRead = reader.read(buffer, 0, buffer.length)) > 0) {
            result.append(buffer, 0, charsRead);
        }
    }

    return result.toString();

}

4. InputStreamReader + BufferedReader (modified line breaks)

The common practice is wrapping the Reader with a BufferedReader.

private static String convertInputStreamToString(InputStream inputStream)
        throws IOException {

    String newLine = System.getProperty("line.separator");
    StringBuilder result = new StringBuilder();
    try (BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream))) {
        String line;
        while ((line = reader.readLine()) != null) {
            result
                    .append(line)
                    .append(newLine);
        }
    }
    return result.toString();

}

5. Java 8 BufferedReader#lines (modified line breaks)

Java 8 added a new lines API to the BufferedReader class to convert all lines into a Stream.

private static String convertInputStreamToString4(InputStream inputStream)
        throws IOException {

    String newLine = System.getProperty("line.separator");
    String result;
    try (Stream<String> lines = new BufferedReader(new InputStreamReader(inputStream)).lines()) {
        result = lines.collect(Collectors.joining(newLine));
    }

    return result;

}

6. Apache Commons IO

If you have the commons-io library in the project, try the IOUtils.toString() to convert InputStream to String.

<dependency>
  <groupId>commons-io</groupId>
  <artifactId>commons-io</artifactId>
  <version>2.11.0</version>
</dependency>

private static String convertInputStreamToString(InputStream inputStream)
  throws IOException {

  return IOUtils.toString(inputStream, StandardCharsets.UTF_8);

}

Review the IOUtils.toString source code, the IOUtils class copy the InputStream into a StringWriter.

package org.apache.commons.io;

public class IOUtils {

  public static String toString(final InputStream input, final Charset charset)
    throws IOException {
    try (final StringBuilderWriter sw = new StringBuilderWriter()) {
        copy(input, sw, charset);
        return sw.toString();
    }
  }

  //...
}

7. Download Source Code

8. References

• ByteArrayOutputStream JavaDoc
• Apache Commons IO
• Convert InputStream to File in Java
• Convert String to InputStream in Java
• Java BufferedReader examples