How do I read / convert an InputStream into a String in Java?
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:
Using
IOUtils.toString
(Apache Utils)String result = IOUtils.toString(inputStream, StandardCharsets.UTF_8);
Using
CharStreams
(Guava)String result = CharStreams.toString(new InputStreamReader( inputStream, Charsets.UTF_8));
Using
Scanner
(JDK)Scanner s = new Scanner(inputStream).useDelimiter("\\A"); String result = s.hasNext() ? s.next() : "";
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"));
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"));
Using
InputStreamReader
andStringBuilder
(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();
Using
StringWriter
andIOUtils.copy
(Apache Commons)StringWriter writer = new StringWriter(); IOUtils.copy(inputStream, writer, "UTF-8"); return writer.toString();
Using
ByteArrayOutputStream
andinputStream.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");
Using
BufferedReader
(JDK). Warning: This solution converts different line breaks (like\n\r
) toline.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();
Using
BufferedInputStream
andByteArrayOutputStream
(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 7return buf.toString("UTF-8");
Using
inputStream.read()
andStringBuilder
(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/op10. BufferedInputStream, ByteArrayOutputStream avgt 10 7,437 ± 0,735 us/op11. 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/op10. BufferedInputStream, ByteArrayOutputStream avgt 10 740,837 ± 5,613 us/op 3. Scanner (JDK) avgt 10 751,417 ± 62,026 us/op11. 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 thatString 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.