If you have a 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 it to a String, so for example I can write that to a log file.

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

public String convertStreamToString(InputStream is) { // ??? } 

62 Answers

Summarize other answers I found 11 main ways to do this (see below). And I wrote some performance tests (see results below):

Ways to convert an InputStream to a String:

 String result = IOUtils.toString(inputStream, StandardCharsets.UTF_8); 

 String result = CharStreams.toString(new InputStreamReader( inputStream, Charsets.UTF_8)); 

 Scanner s = new Scanner(inputStream).useDelimiter("\\A"); String result = s.hasNext() ? s.next() : ""; 

 String result = new BufferedReader(new InputStreamReader(inputStream)) .lines().collect(Collectors.joining("\n")); 

 String result = new BufferedReader(new InputStreamReader(inputStream)) .lines().parallel().collect(Collectors.joining("\n")); 

 int bufferSize = 1024; char[] buffer = new char[bufferSize]; StringBuilder out = new StringBuilder(); Reader in = new InputStreamReader(stream, StandardCharsets.UTF_8); for (int numRead; (numRead = in.read(buffer, 0, buffer.length)) > 0; ) { out.append(buffer, 0, numRead); } return out.toString(); 

 StringWriter writer = new StringWriter(); IOUtils.copy(inputStream, writer, "UTF-8"); return writer.toString(); 

 ByteArrayOutputStream result = new ByteArrayOutputStream(); byte[] buffer = new byte[1024]; for (int length; (length = inputStream.read(buffer)) != -1; ) { result.write(buffer, 0, length); } // StandardCharsets.UTF_8.name() > JDK 7 return result.toString("UTF-8"); 

 String newLine = System.getProperty("line.separator"); BufferedReader reader = new BufferedReader( new InputStreamReader(inputStream)); StringBuilder result = new StringBuilder(); for (String line; (line = reader.readLine()) != null; ) { if (result.length() > 0) { result.append(newLine); } result.append(line); } return result.toString(); 

BufferedInputStream bis = new BufferedInputStream(inputStream); ByteArrayOutputStream buf = new ByteArrayOutputStream(); for (int result = bis.read(); result != -1; result = bis.read()) { buf.write((byte) result); } // StandardCharsets.UTF_8.name() > JDK 7 return buf.toString("UTF-8"); 

StringBuilder sb = new StringBuilder(); for (int ch; (ch = inputStream.read()) != -1; ) { sb.append((char) ch); } return sb.toString(); 

Warning:

Performance tests

Performance tests for small String (length = 175), url in github (mode = Average Time, system = Linux, score 1,343 is the best):

 Benchmark Mode Cnt Score Error Units 8. ByteArrayOutputStream and read (JDK) avgt 10 1,343 ± 0,028 us/op 6. InputStreamReader and StringBuilder (JDK) avgt 10 6,980 ± 0,404 us/op 10. BufferedInputStream, ByteArrayOutputStream avgt 10 7,437 ± 0,735 us/op 11. InputStream.read() and StringBuilder (JDK) avgt 10 8,977 ± 0,328 us/op 7. StringWriter and IOUtils.copy (Apache) avgt 10 10,613 ± 0,599 us/op 1. IOUtils.toString (Apache Utils) avgt 10 10,605 ± 0,527 us/op 3. Scanner (JDK) avgt 10 12,083 ± 0,293 us/op 2. CharStreams (guava) avgt 10 12,999 ± 0,514 us/op 4. Stream Api (Java 8) avgt 10 15,811 ± 0,605 us/op 9. BufferedReader (JDK) avgt 10 16,038 ± 0,711 us/op 5. parallel Stream Api (Java 8) avgt 10 21,544 ± 0,583 us/op 

Performance tests for big String (length = 50100), url in github (mode = Average Time, system = Linux, score 200,715 is the best):

 Benchmark Mode Cnt Score Error Units 8. ByteArrayOutputStream and read (JDK) avgt 10 200,715 ± 18,103 us/op 1. IOUtils.toString (Apache Utils) avgt 10 300,019 ± 8,751 us/op 6. InputStreamReader and StringBuilder (JDK) avgt 10 347,616 ± 130,348 us/op 7. StringWriter and IOUtils.copy (Apache) avgt 10 352,791 ± 105,337 us/op 2. CharStreams (guava) avgt 10 420,137 ± 59,877 us/op 9. BufferedReader (JDK) avgt 10 632,028 ± 17,002 us/op 5. parallel Stream Api (Java 8) avgt 10 662,999 ± 46,199 us/op 4. Stream Api (Java 8) avgt 10 701,269 ± 82,296 us/op 10. BufferedInputStream, ByteArrayOutputStream avgt 10 740,837 ± 5,613 us/op 3. Scanner (JDK) avgt 10 751,417 ± 62,026 us/op 11. InputStream.read() and StringBuilder (JDK) avgt 10 2919,350 ± 1101,942 us/op 

Graphs (performance tests depending on Input Stream length in Windows 7 system)

Performance test (Average Time) depending on Input Stream length in Windows 7 system:

 length 182 546 1092 3276 9828 29484 58968 test8 0.38 0.938 1.868 4.448 13.412 36.459 72.708 test4 2.362 3.609 5.573 12.769 40.74 81.415 159.864 test5 3.881 5.075 6.904 14.123 50.258 129.937 166.162 test9 2.237 3.493 5.422 11.977 45.98 89.336 177.39 test6 1.261 2.12 4.38 10.698 31.821 86.106 186.636 test7 1.601 2.391 3.646 8.367 38.196 110.221 211.016 test1 1.529 2.381 3.527 8.411 40.551 105.16 212.573 test3 3.035 3.934 8.606 20.858 61.571 118.744 235.428 test2 3.136 6.238 10.508 33.48 43.532 118.044 239.481 test10 1.593 4.736 7.527 20.557 59.856 162.907 323.147 test11 3.913 11.506 23.26 68.644 207.591 600.444 1211.545 

A nice way to do this is using Apache commons IOUtils to copy the InputStream into a StringWriter... something like

StringWriter writer = new StringWriter(); IOUtils.copy(inputStream, writer, encoding); String theString = writer.toString(); 

or even

// NB: does not close inputStream, you'll have to use try-with-resources for that String theString = IOUtils.toString(inputStream, encoding); 

Alternatively, you could use ByteArrayOutputStream if you don't want to mix your Streams and Writers

Here's a way using only the standard Java library (note that the stream is not closed, your mileage may vary).

static String convertStreamToString(java.io.InputStream is) { java.util.Scanner s = new java.util.Scanner(is).useDelimiter("\\A"); return s.hasNext() ? s.next() : ""; } 

I learned this trick from "Stupid Scanner tricks" article. The reason it works is because Scanner iterates over tokens in the stream, and in this case we separate tokens using "beginning of the input boundary" (\A), thus giving us only one token for the entire contents of the stream.

Note, if you need to be specific about the input stream's encoding, you can provide the second argument to Scanner constructor that indicates what character set to use (e.g. "UTF-8").

Hat tip goes also to Jacob, who once pointed me to the said article.

Apache Commons allows:

String myString = IOUtils.toString(myInputStream, "UTF-8"); 

Of course, you could choose other character encodings besides UTF-8.

Also see: (documentation)

Taking into account file one should first get a java.io.Reader instance. This can then be read and added to a StringBuilder (we don't need StringBuffer if we are not accessing it in multiple threads, and StringBuilder is faster). The trick here is that we work in blocks, and as such don't need other buffering streams. The block size is parameterized for run-time performance optimization.

public static String slurp(final InputStream is, final int bufferSize) { final char[] buffer = new char[bufferSize]; final StringBuilder out = new StringBuilder(); try (Reader in = new InputStreamReader(is, "UTF-8")) { for (;;) { int rsz = in.read(buffer, 0, buffer.length); if (rsz < 0) break; out.append(buffer, 0, rsz); } } catch (UnsupportedEncodingException ex) { /* ... */ } catch (IOException ex) { /* ... */ } return out.toString(); } 

Use:

InputStream in = /* Your InputStream */; StringBuilder sb = new StringBuilder(); BufferedReader br = new BufferedReader(new InputStreamReader(in)); String read; while ((read=br.readLine()) != null) { //System.out.println(read); sb.append(read); } br.close(); return sb.toString(); 

If you are using Google-Collections/Guava you could do the following:

InputStream stream = ... String content = CharStreams.toString(new InputStreamReader(stream, Charsets.UTF_8)); Closeables.closeQuietly(stream); 

Note that the second parameter (i.e. Charsets.UTF_8) for the InputStreamReader isn't necessary, but it is generally a good idea to specify the encoding if you know it (which you should!)

For completeness here is Java 9 solution:

public static String toString(InputStream input) throws IOException { return new String(input.readAllBytes(), StandardCharsets.UTF_8); } 

This uses the readAllBytes method which was added to Java 9.

This is the best pure Java solution that fits perfectly for Android and any other JVM.

This solution works amazingly well... it is simple, fast, and works on small and large streams just the same!! (see benchmark above.. No. 8)

public String readFullyAsString(InputStream inputStream, String encoding) throws IOException { return readFully(inputStream).toString(encoding); } public byte[] readFullyAsBytes(InputStream inputStream) throws IOException { return readFully(inputStream).toByteArray(); } private ByteArrayOutputStream readFully(InputStream inputStream) throws IOException { ByteArrayOutputStream baos = new ByteArrayOutputStream(); byte[] buffer = new byte[1024]; int length = 0; while ((length = inputStream.read(buffer)) != -1) { baos.write(buffer, 0, length); } return baos; } 

Use:

import java.io.BufferedInputStream; import java.io.ByteArrayOutputStream; import java.io.InputStream; import java.io.IOException; public static String readInputStreamAsString(InputStream in) throws IOException { BufferedInputStream bis = new BufferedInputStream(in); ByteArrayOutputStream buf = new ByteArrayOutputStream(); int result = bis.read(); while(result != -1) { byte b = (byte)result; buf.write(b); result = bis.read(); } return buf.toString(); } 

Here's the most elegant, pure-Java (no library) solution I came up with after some experimentation:

public static String fromStream(InputStream in) throws IOException { BufferedReader reader = new BufferedReader(new InputStreamReader(in)); StringBuilder out = new StringBuilder(); String newLine = System.getProperty("line.separator"); String line; while ((line = reader.readLine()) != null) { out.append(line); out.append(newLine); } return out.toString(); } 

I did a benchmark upon 14 distinct answers here (sorry for not providing credits but there are too many duplicates).

The result is very surprising. It turns out that Apache IOUtils is the slowest and ByteArrayOutputStream is the fastest solutions:

So first here is the best method:

public String inputStreamToString(InputStream inputStream) throws IOException { try(ByteArrayOutputStream result = new ByteArrayOutputStream()) { byte[] buffer = new byte[1024]; int length; while ((length = inputStream.read(buffer)) != -1) { result.write(buffer, 0, length); } return result.toString(UTF_8); } } 

Benchmark results, of 20 MB random bytes in 20 cycles

Time in milliseconds

• ByteArrayOutputStreamTest: 194
• NioStream: 198
• Java9ISTransferTo: 201
• Java9ISReadAllBytes: 205
• BufferedInputStreamVsByteArrayOutputStream: 314
• ApacheStringWriter2: 574
• GuavaCharStreams: 589
• ScannerReaderNoNextTest: 614
• ScannerReader: 633
• ApacheStringWriter: 1544
• StreamApi: Error
• ParallelStreamApi: Error
• BufferReaderTest: Error
• InputStreamAndStringBuilder: Error

Benchmark source code

import com.google.common.io.CharStreams; import org.apache.commons.io.IOUtils; import java.io.*; import java.nio.ByteBuffer; import java.nio.channels.Channels; import java.nio.channels.ReadableByteChannel; import java.nio.channels.WritableByteChannel; import java.util.Arrays; import java.util.List; import java.util.Random; import java.util.stream.Collectors; /** * Created by Ilya Gazman on 2/13/18. */ public class InputStreamToString { private static final String UTF_8 = "UTF-8"; public static void main(String... args) { log("App started"); byte[] bytes = new byte[1024 * 1024]; new Random().nextBytes(bytes); log("Stream is ready\n"); try { test(bytes); } catch (IOException e) { e.printStackTrace(); } } private static void test(byte[] bytes) throws IOException { List<Stringify> tests = Arrays.asList( new ApacheStringWriter(), new ApacheStringWriter2(), new NioStream(), new ScannerReader(), new ScannerReaderNoNextTest(), new GuavaCharStreams(), new StreamApi(), new ParallelStreamApi(), new ByteArrayOutputStreamTest(), new BufferReaderTest(), new BufferedInputStreamVsByteArrayOutputStream(), new InputStreamAndStringBuilder(), new Java9ISTransferTo(), new Java9ISReadAllBytes() ); String solution = new String(bytes, "UTF-8"); for (Stringify test : tests) { try (ByteArrayInputStream inputStream = new ByteArrayInputStream(bytes)) { String s = test.inputStreamToString(inputStream); if (!s.equals(solution)) { log(test.name() + ": Error"); continue; } } long startTime = System.currentTimeMillis(); for (int i = 0; i < 20; i++) { try (ByteArrayInputStream inputStream = new ByteArrayInputStream(bytes)) { test.inputStreamToString(inputStream); } } log(test.name() + ": " + (System.currentTimeMillis() - startTime)); } } private static void log(String message) { System.out.println(message); } interface Stringify { String inputStreamToString(InputStream inputStream) throws IOException; default String name() { return this.getClass().getSimpleName(); } } static class ApacheStringWriter implements Stringify { @Override public String inputStreamToString(InputStream inputStream) throws IOException { StringWriter writer = new StringWriter(); IOUtils.copy(inputStream, writer, UTF_8); return writer.toString(); } } static class ApacheStringWriter2 implements Stringify { @Override public String inputStreamToString(InputStream inputStream) throws IOException { return IOUtils.toString(inputStream, UTF_8); } } static class NioStream implements Stringify { @Override public String inputStreamToString(InputStream in) throws IOException { ReadableByteChannel channel = Channels.newChannel(in); ByteBuffer byteBuffer = ByteBuffer.allocate(1024 * 16); ByteArrayOutputStream bout = new ByteArrayOutputStream(); WritableByteChannel outChannel = Channels.newChannel(bout); while (channel.read(byteBuffer) > 0 || byteBuffer.position() > 0) { byteBuffer.flip(); //make buffer ready for write outChannel.write(byteBuffer); byteBuffer.compact(); //make buffer ready for reading } channel.close(); outChannel.close(); return bout.toString(UTF_8); } } static class ScannerReader implements Stringify { @Override public String inputStreamToString(InputStream is) throws IOException { java.util.Scanner s = new java.util.Scanner(is).useDelimiter("\\A"); return s.hasNext() ? s.next() : ""; } } static class ScannerReaderNoNextTest implements Stringify { @Override public String inputStreamToString(InputStream is) throws IOException { java.util.Scanner s = new java.util.Scanner(is).useDelimiter("\\A"); return s.next(); } } static class GuavaCharStreams implements Stringify { @Override public String inputStreamToString(InputStream is) throws IOException { return CharStreams.toString(new InputStreamReader( is, UTF_8)); } } static class StreamApi implements Stringify { @Override public String inputStreamToString(InputStream inputStream) throws IOException { return new BufferedReader(new InputStreamReader(inputStream)) .lines().collect(Collectors.joining("\n")); } } static class ParallelStreamApi implements Stringify { @Override public String inputStreamToString(InputStream inputStream) throws IOException { return new BufferedReader(new InputStreamReader(inputStream)).lines() .parallel().collect(Collectors.joining("\n")); } } static class ByteArrayOutputStreamTest implements Stringify { @Override public String inputStreamToString(InputStream inputStream) throws IOException { try(ByteArrayOutputStream result = new ByteArrayOutputStream()) { byte[] buffer = new byte[1024]; int length; while ((length = inputStream.read(buffer)) != -1) { result.write(buffer, 0, length); } return result.toString(UTF_8); } } } static class BufferReaderTest implements Stringify { @Override public String inputStreamToString(InputStream inputStream) throws IOException { String newLine = System.getProperty("line.separator"); BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream)); StringBuilder result = new StringBuilder(UTF_8); String line; boolean flag = false; while ((line = reader.readLine()) != null) { result.append(flag ? newLine : "").append(line); flag = true; } return result.toString(); } } static class BufferedInputStreamVsByteArrayOutputStream implements Stringify { @Override public String inputStreamToString(InputStream inputStream) throws IOException { BufferedInputStream bis = new BufferedInputStream(inputStream); ByteArrayOutputStream buf = new ByteArrayOutputStream(); int result = bis.read(); while (result != -1) { buf.write((byte) result); result = bis.read(); } return buf.toString(UTF_8); } } static class InputStreamAndStringBuilder implements Stringify { @Override public String inputStreamToString(InputStream inputStream) throws IOException { int ch; StringBuilder sb = new StringBuilder(UTF_8); while ((ch = inputStream.read()) != -1) sb.append((char) ch); return sb.toString(); } } static class Java9ISTransferTo implements Stringify { @Override public String inputStreamToString(InputStream inputStream) throws IOException { ByteArrayOutputStream bos = new ByteArrayOutputStream(); inputStream.transferTo(bos); return bos.toString(UTF_8); } } static class Java9ISReadAllBytes implements Stringify { @Override public String inputStreamToString(InputStream inputStream) throws IOException { return new String(inputStream.readAllBytes(), UTF_8); } } } 

I'd use some Java 8 tricks.

public static String streamToString(final InputStream inputStream) throws Exception { // buffering optional try ( final BufferedReader br = new BufferedReader(new InputStreamReader(inputStream)) ) { // parallel optional return br.lines().parallel().collect(Collectors.joining("\n")); } catch (final IOException e) { throw new RuntimeException(e); // whatever. } } 

Essentially the same as some other answers except more succinct.

I ran some timing tests because time matters, always.

I attempted to get the response into a String 3 different ways. (shown below)
I left out try/catch blocks for the sake readability.

To give context, this is the preceding code for all 3 approaches:

 String response; String url = "www.blah.com/path?key=value"; GetMethod method = new GetMethod(url); int status = client.executeMethod(method); 

1)

 response = method.getResponseBodyAsString(); 

2)

InputStream resp = method.getResponseBodyAsStream(); InputStreamReader is=new InputStreamReader(resp); BufferedReader br=new BufferedReader(is); String read = null; StringBuffer sb = new StringBuffer(); while((read = br.readLine()) != null) { sb.append(read); } response = sb.toString(); 

3)

InputStream iStream = method.getResponseBodyAsStream(); StringWriter writer = new StringWriter(); IOUtils.copy(iStream, writer, "UTF-8"); response = writer.toString(); 

So, after running 500 tests on each approach with the same request/response data, here are the numbers. Once again, these are my findings and your findings may not be exactly the same, but I wrote this to give some indication to others of the efficiency differences of these approaches.

Ranks:
Approach #1
Approach #3 - 2.6% slower than #1
Approach #2 - 4.3% slower than #1

Any of these approaches is an appropriate solution for grabbing a response and creating a String from it.

Pure Java solution using Streams, works since Java 8.

import java.io.BufferedReader; import java.io.IOException; import java.io.InputStream; import java.io.InputStreamReader; import java.util.stream.Collectors; // ... public static String inputStreamToString(InputStream is) throws IOException { try (BufferedReader br = new BufferedReader(new InputStreamReader(is))) { return br.lines().collect(Collectors.joining(System.lineSeparator())); } } 

As mentioned by Christoffer Hammarström below other answer it is safer to explicitly specify the Charset. I.e. The InputStreamReader constructor can be changes as follows:

new InputStreamReader(is, Charset.forName("UTF-8")) 

Here's more-or-less sampath's answer, cleaned up a bit and represented as a function:

String streamToString(InputStream in) throws IOException { StringBuilder out = new StringBuilder(); BufferedReader br = new BufferedReader(new InputStreamReader(in)); for(String line = br.readLine(); line != null; line = br.readLine()) out.append(line); br.close(); return out.toString(); } 

If you were feeling adventurous, you could mix Scala and Java and end up with this:

scala.io.Source.fromInputStream(is).mkString("") 

Mixing Java and Scala code and libraries has it's benefits.

See full description here: Idiomatic way to convert an InputStream to a String in Scala

If you can't use Commons IO (FileUtils/IOUtils/CopyUtils), here's an example using a BufferedReader to read the file line by line:

public class StringFromFile { public static void main(String[] args) /*throws UnsupportedEncodingException*/ { InputStream is = StringFromFile.class.getResourceAsStream("file.txt"); BufferedReader br = new BufferedReader(new InputStreamReader(is/*, "UTF-8"*/)); final int CHARS_PER_PAGE = 5000; //counting spaces StringBuilder builder = new StringBuilder(CHARS_PER_PAGE); try { for(String line=br.readLine(); line!=null; line=br.readLine()) { builder.append(line); builder.append('\n'); } } catch (IOException ignore) { } String text = builder.toString(); System.out.println(text); } } 

Or if you want raw speed I'd propose a variation on what Paul de Vrieze suggested (which avoids using a StringWriter (which uses a StringBuffer internally):

public class StringFromFileFast { public static void main(String[] args) /*throws UnsupportedEncodingException*/ { InputStream is = StringFromFileFast.class.getResourceAsStream("file.txt"); InputStreamReader input = new InputStreamReader(is/*, "UTF-8"*/); final int CHARS_PER_PAGE = 5000; //counting spaces final char[] buffer = new char[CHARS_PER_PAGE]; StringBuilder output = new StringBuilder(CHARS_PER_PAGE); try { for(int read = input.read(buffer, 0, buffer.length); read != -1; read = input.read(buffer, 0, buffer.length)) { output.append(buffer, 0, read); } } catch (IOException ignore) { } String text = output.toString(); System.out.println(text); } } 

Use the java.io.InputStream.transferTo(OutputStream) supported in Java 9 and the ByteArrayOutputStream.toString(String) which takes the charset name:

public static String gobble(InputStream in, String charsetName) throws IOException { ByteArrayOutputStream bos = new ByteArrayOutputStream(); in.transferTo(bos); return bos.toString(charsetName); } 

Make sure to close the streams at end if you use Stream Readers

private String readStream(InputStream iStream) throws IOException { //build a Stream Reader, it can read char by char InputStreamReader iStreamReader = new InputStreamReader(iStream); //build a buffered Reader, so that i can read whole line at once BufferedReader bReader = new BufferedReader(iStreamReader); String line = null; StringBuilder builder = new StringBuilder(); while((line = bReader.readLine()) != null) { //Read till end builder.append(line); builder.append("\n"); // append new line to preserve lines } bReader.close(); //close all opened stuff iStreamReader.close(); //iStream.close(); //EDIT: Let the creator of the stream close it! // some readers may auto close the inner stream return builder.toString(); } 

EDIT: On JDK 7+, you can use try-with-resources construct.

/** * Reads the stream into a string * @param iStream the input stream * @return the string read from the stream * @throws IOException when an IO error occurs */ private String readStream(InputStream iStream) throws IOException { //Buffered reader allows us to read line by line try (BufferedReader bReader = new BufferedReader(new InputStreamReader(iStream))){ StringBuilder builder = new StringBuilder(); String line; while((line = bReader.readLine()) != null) { //Read till end builder.append(line); builder.append("\n"); // append new line to preserve lines } return builder.toString(); } } 

This is an answer adapted from org.apache.commons.io.IOUtils source code, for those who want to have the apache implementation but do not want the whole library.

private static final int BUFFER_SIZE = 4 * 1024; public static String inputStreamToString(InputStream inputStream, String charsetName) throws IOException { StringBuilder builder = new StringBuilder(); InputStreamReader reader = new InputStreamReader(inputStream, charsetName); char[] buffer = new char[BUFFER_SIZE]; int length; while ((length = reader.read(buffer)) != -1) { builder.append(buffer, 0, length); } return builder.toString(); } 

This one is nice because:

• It safely handles the Charset.
• You control the read buffer size.
• You can provision the length of the builder and it doesn't have to be an exact value.
• Is free from library dependencies.
• Is for Java 7 or higher.

How to do it?

public static String convertStreamToString(InputStream is) throws IOException { StringBuilder sb = new StringBuilder(2048); // Define a size if you have an idea of it. char[] read = new char[128]; // Your buffer size. try (InputStreamReader ir = new InputStreamReader(is, StandardCharsets.UTF_8)) { for (int i; -1 != (i = ir.read(read)); sb.append(read, 0, i)); } return sb.toString(); } 

For JDK 9

public static String inputStreamString(InputStream inputStream) throws IOException { try (inputStream) { return new String(inputStream.readAllBytes(), StandardCharsets.UTF_8); } } 

String inputStreamToString(InputStream inputStream, Charset charset) throws IOException { try ( final StringWriter writer = new StringWriter(); final InputStreamReader reader = new InputStreamReader(inputStream, charset) ) { reader.transferTo(writer); return writer.toString(); } } 

• pure Java standard library solution - no libs
• since Java 10 - Reader#transferTo(java.io.Writer)
• loopless solution
• no new line character handling

Here is the complete method for converting InputStream into String without using any third party library. Use StringBuilder for single threaded environment otherwise use StringBuffer.

public static String getString( InputStream is) throws IOException { int ch; StringBuilder sb = new StringBuilder(); while((ch = is.read()) != -1) sb.append((char)ch); return sb.toString(); } 

Another one, for all the Spring users:

import java.nio.charset.StandardCharsets; import org.springframework.util.FileCopyUtils; public String convertStreamToString(InputStream is) throws IOException { return new String(FileCopyUtils.copyToByteArray(is), StandardCharsets.UTF_8); } 

The utility methods in org.springframework.util.StreamUtils are similar to the ones in FileCopyUtils, but they leave the stream open when done.

Here's how to do it using just the JDK using byte array buffers. This is actually how the commons-io IOUtils.copy() methods all work. You can replace byte[] with char[] if you're copying from a Reader instead of an InputStream.

import java.io.ByteArrayOutputStream; import java.io.InputStream; ... InputStream is = .... ByteArrayOutputStream baos = new ByteArrayOutputStream(8192); byte[] buffer = new byte[8192]; int count = 0; try { while ((count = is.read(buffer)) != -1) { baos.write(buffer, 0, count); } } finally { try { is.close(); } catch (Exception ignore) { } } String charset = "UTF-8"; String inputStreamAsString = baos.toString(charset); 

Kotlin users simply do:

println(InputStreamReader(is).readText()) 

whereas

readText() 

is Kotlin standard library’s built-in extension method.

The easiest way in JDK is with the following code snipplets.

String convertToString(InputStream in){ String resource = new Scanner(in).useDelimiter("\\Z").next(); return resource; } 

In terms of reduce, and concat it can be expressed in Java 8 as:

String fromFile = new BufferedReader(new InputStreamReader(inputStream)).lines().reduce(String::concat).get(); 

Here's my Java 8 based solution, which uses the new Stream API to collect all lines from an InputStream:

public static String toString(InputStream inputStream) { BufferedReader reader = new BufferedReader( new InputStreamReader(inputStream)); return reader.lines().collect(Collectors.joining( System.getProperty("line.separator"))); } 

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