Ler / converter um InputStream em um String

Se você tem um object java.io.InputStream , como você deve processar esse object e produzir uma String ?


Suponha que eu tenha um InputStream que contém dados de texto, e eu quero convertê-lo em uma String , por exemplo, eu posso escrever isso em um arquivo de log.

Qual é a maneira mais fácil de InputStream o InputStream e convertê-lo em String ?

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

Uma boa maneira de fazer isso é usando o IOUtils Apache commons para copiar o InputStream em um StringWriter … algo como

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

ou até mesmo

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

Alternativamente, você poderia usar ByteArrayOutputStream se não quiser misturar seus Streams e Writers

Aqui está uma maneira de usar apenas a biblioteca Java padrão (observe que o stream não está fechado, YMMV).

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

Eu aprendi esse truque com o artigo “Stupid Scanner tricks” . O motivo pelo qual isso funciona é porque o Scanner repete os tokens no stream e, nesse caso, separamos os tokens usando “início do limite de input” (\ A), fornecendo apenas um token para todo o conteúdo do stream.

Note, se você precisa ser específico sobre a codificação do stream de input, você pode fornecer o segundo argumento para o construtor Scanner que indica qual conjunto de caracteres usar (por exemplo, “UTF-8”).

A dica do chapéu vai também para Jacob, que certa vez me indicou o artigo.

EDITED: Graças a uma sugestão de Patrick , tornou a function mais robusta ao lidar com um stream de input vazio. Mais uma edição: try / catch nixed, o caminho de Patrick é mais lacônico.

Resuma outras respostas Encontrei 11 maneiras principais de fazer isso (veja abaixo). E eu escrevi alguns testes de desempenho (veja os resultados abaixo):

Formas de converter um InputStream em um String:

  1. Usando IOUtils.toString (Apache Utils)

     String result = IOUtils.toString(inputStream, StandardCharsets.UTF_8); 
  2. Usando CharStreams (goiaba)

     String result = CharStreams.toString(new InputStreamReader( inputStream, Charsets.UTF_8)); 
  3. Usando o Scanner (JDK)

     Scanner s = new Scanner(inputStream).useDelimiter("\\A"); String result = s.hasNext() ? s.next() : ""; 
  4. Usando a API do Stream (Java 8). Aviso : esta solução converte diferentes quebras de linha (como \r\n ) em \n .

     String result = new BufferedReader(new InputStreamReader(inputStream)) .lines().collect(Collectors.joining("\n")); 
  5. Usando a API de stream paralela (Java 8). Aviso : esta solução converte diferentes quebras de linha (como \r\n ) em \n .

     String result = new BufferedReader(new InputStreamReader(inputStream)).lines() .parallel().collect(Collectors.joining("\n")); 
  6. Usando InputStreamReader e 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. Usando StringWriter e IOUtils.copy (Apache Commons)

     StringWriter writer = new StringWriter(); IOUtils.copy(inputStream, writer, "UTF-8"); return writer.toString(); 
  8. Usando ByteArrayOutputStream e 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. Usando o BufferedReader (JDK). Aviso: Esta solução converte diferentes quebras de linha (como \n\r ) para a propriedade do sistema line.separator (por exemplo, no Windows para "\ 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. Usando BufferedInputStream e 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. Usando inputStream.read() e StringBuilder (JDK). Aviso : esta solução tem problemas com o Unicode, por exemplo, com texto em russo (funciona corretamente somente com texto não-Unicode)

     int ch; StringBuilder sb = new StringBuilder(); while((ch = inputStream.read()) != -1) sb.append((char)ch); reset(); return sb.toString(); 

Aviso :

  1. As soluções 4, 5 e 9 convertem diferentes quebras de linha em uma.

  2. A solução 11 não pode funcionar corretamente com texto Unicode

Testes de performance

Testes de desempenho para String pequena (length = 175), url no github (mode = Average Time, system = Linux, pontuação 1.343 é a melhor):

  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 

Testes de desempenho para grandes String (comprimento = 50100), url no github (modo = tempo médio, sistema = Linux, pontuação 200.715 é o melhor):

  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 

Gráficos (testes de desempenho dependendo do tamanho do stream de input no sistema Windows 7)
insira a descrição da imagem aqui

Teste de desempenho (tempo médio) dependendo do comprimento do stream de input no sistema Windows 7:

  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 

O Apache Commons permite:

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

Claro, você poderia escolher outras codificações de caracteres além do UTF-8.

Veja também: ( Docs )

Levando em consideração o arquivo, um deve primeiro obter uma instância de java.io.Reader . Isso pode então ser lido e adicionado a um StringBuilder (não precisamos de StringBuffer se não estivermos acessando-o em vários threads e o StringBuilder for mais rápido). O truque aqui é que trabalhamos em blocos e, como tal, não precisamos de outros streams de buffering. O tamanho do bloco é parametrizado para otimização do desempenho em tempo de execução.

 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(); } 

Que tal agora?

 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(); 

Se você estiver usando o Google-Collections / Guava, faça o seguinte:

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

Note que o segundo parâmetro (isto é, Charsets.UTF_8) para o InputStreamReader não é necessário, mas geralmente é uma boa idéia especificar a codificação se você a souber (o que você deve!)

Esta é a minha solução Java & Android pura, funciona bem …

 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; } 

E se:

 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(); } 

Aqui está a solução mais elegante e pura Java (sem biblioteca) que eu criei após algumas experiências:

 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(); } 

Para completar, aqui está a solução Java 9 :

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

O readAllBytes está atualmente na base de código principal do JDK 9, portanto é provável que apareça na versão. Você pode tentar agora usando as compilações de snapshots do JDK 9 .

Eu usaria alguns truques do Java 8.

 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. } } 

Essencialmente o mesmo que algumas outras respostas, exceto mais sucintas.

Eu fiz alguns testes de tempo porque o tempo é importante, sempre.

Eu tentei obter a resposta em uma String 3 maneiras diferentes. (mostrado abaixo)
Eu deixei de tentar / bloquear blocos para a legibilidade do bem.

Para dar contexto, este é o código anterior para todas as três abordagens:

  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(); 

Então, depois de executar 500 testes em cada abordagem com os mesmos dados de solicitação / resposta, aqui estão os números. Mais uma vez, estas são minhas descobertas e suas descobertas podem não ser exatamente as mesmas, mas escrevi isso para dar alguma indicação a outras pessoas sobre as diferenças de eficiência dessas abordagens.

Pontos:
Abordagem nº 1
Abordagem nº 3 – 2,6% mais lenta que a nº 1
Abordagem nº 2 – 4,3% mais lenta que a nº 1

Qualquer uma dessas abordagens é uma solução apropriada para pegar uma resposta e criar uma String a partir dela.

Solução Java pura usando o Stream s, funciona desde o 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())); } } 

Como mencionado por Christoffer Hammarström abaixo de outra resposta , é mais seguro especificar explicitamente o Charset . Ou seja, o construtor InputStreamReader pode ser alterado da seguinte forma:

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

Eu fiz uma referência em 14 respostas distintas aqui (Desculpe por não fornecer créditos, mas há muitos duplicados)

O resultado é muito surpreendente. Acontece que o Apache IOUtils é o mais lento e o ByteArrayOutputStream é o mais rápido:

Então, primeiro aqui é o melhor método:

 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); } } 

Resultados de benchmark, de 20MB de bytes randoms em 20 ciclos

Tempo em milissegundos

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

Código-fonte de referência

 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 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); } } } 

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); } } 

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(); } 

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(); } } 

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(); } 

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()) 

enquanto que

 readText() 

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

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.

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); } 

This one is nice because:

  • Hand safety the Charset.
  • You control the read buffer size.
  • You can provision the length of the builder and can be not exactly.
  • Is free from library dependencies.
  • Is for Java 7 or higher.

What the for?

 public static String convertStreamToString(InputStream is) { if (is == null) return null; 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)); } catch (Throwable t) {} return sb.toString(); } 

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"))); } 

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; } 

Guava provides much shorter efficient autoclosing solution in case when input stream comes from classpath resource (which seems to be popular task):

 byte[] bytes = Resources.toByteArray(classLoader.getResource(path)); 

ou

 String text = Resources.toString(classLoader.getResource(path), StandardCharsets.UTF_8); 

There is also general concept of ByteSource and CharSource that gently take care of both opening and closing the stream.

So, for example, instead of explicitly opening a small file to read its contents:

 String content = Files.asCharSource(new File("robots.txt"), StandardCharsets.UTF_8).read(); byte[] data = Files.asByteSource(new File("favicon.ico")).read(); 

ou apenas

 String content = Files.toString(new File("robots.txt"), StandardCharsets.UTF_8); byte[] data = Files.toByteArray(new File("favicon.ico")); 

The below code worked for me.

 URL url = MyClass.class.getResource("/" + configFileName); BufferedInputStream bi = (BufferedInputStream) url.getContent(); byte[] buffer = new byte[bi.available() ]; int bytesRead = bi.read(buffer); String out = new String(buffer); 

Please note, according to Java docs, the available() method might not work with InputStream but always works with BufferedInputStream . In case you don’t want to use available() method we can always use the below code

 URL url = MyClass.class.getResource("/" + configFileName); BufferedInputStream bi = (BufferedInputStream) url.getContent(); File f = new File(url.getPath()); byte[] buffer = new byte[ (int) f.length()]; int bytesRead = bi.read(buffer); String out = new String(buffer); 

I am not sure if there will be any encoding issues. Please comment, if there will be any issues with the code.