Sample query:
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) {
// ???
}How to convert InputStream object into String in Java? Answer #1:
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:
#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 converts 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 converts 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)
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();#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];
for (int length; (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 converts 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();
for (String line; (line = reader.readLine()) != null; ) {
if (result.length() > 0) {
result.append(newLine);
}
result.append(line);
}
return result.toString();#10: Using BufferedInputStream and ByteArrayOutputStream (JDK)
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");#11: Using inputStream.read() and StringBuilder (JDK). Warning: This solution has problems with Unicode, for example with Russian text (works correctly only with non-Unicode text)
StringBuilder sb = new StringBuilder();
for (int ch; (ch = inputStream.read()) != -1; ) {
sb.append((char) ch);
}
return sb.toString();Warning:
- Solutions 4, 5 and 9 convert different line breaks to one.
- Solution 11 can’t work correctly with Unicode text
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 1211.545Answer #2:
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.
Answer #3:
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”).
Answer #4:
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();
}Answer #5:
Use the code below:
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();
Convert InputStream to String- Answer #6:
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;
}Answer #7:
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);
}
}
}
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