提问



如果你有一个java.io.InputStream对象,你应该如何处理该对象并产生String?





假设我有InputStream包含文本数据,我想将其转换为String,例如我可以将其写入日志文件。


采用InputStream并将其转换为String的最简单方法是什么?


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

最佳参考


一个很好的方法是使用Apache commons IOUtilsInputStream复制到StringWriter ......像[115]这样的东西


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


甚至


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


或者,如果你不想混合你的Streams和Writers,你可以使用ByteArrayOutputStream

其它参考1


这是一种仅使用标准Java库的方法(注意流未关闭,YMMV)。


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


我从Stupid Scanner tricks文章中学到了这个技巧。它工作的原因是因为Scanner迭代了流中的标记,在这种情况下,我们使用输入边界的开头(\\ A)分隔标记,因此只为流的整个内容提供了一个标记。[116] [117]


注意,如果您需要具体了解输入流的编码,可以为Scanner构造函数提供第二个参数,指示要使用的字符集(例如UTF-8)。


帽子小贴士也向Jacob提出,他曾经指出我所说的那篇文章。


已编辑:感谢Patrick的建议,在处理空输入流时使该功能更加强大。 另一个编辑: nixed try/catch,帕特里克的方式更简洁。

其它参考2


总结其他答案我找到了11种主要方法(见下文)。我写了一些性能测试(见下面的结果):


将InputStream转换为String的方法:



  1. 使用IOUtils.toString(Apache Utils)


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

  2. 使用CharStreams(番石榴)


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

  3. 使用Scanner(JDK)


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

  4. 使用 Stream API (Java 8)。 警告:此解决方案将不同的换行符(如\r\n)转换为\n


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

  5. 使用并行Stream API (Java 8)。 警告:此解决方案将不同的换行符(如\r\n)转换为\n


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

  6. 使用InputStreamReaderStringBuilder(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. 使用StringWriterIOUtils.copy(Apache Commons)


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

  8. 使用ByteArrayOutputStreaminputStream.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. 使用BufferedReader(JDK)。 警告:此解决方案将不同的换行符(如\n\r)转换为line.separator系统属性(例如,在Windows中转换为\\ 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. 使用BufferedInputStreamByteArrayOutputStream(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. 使用inputStream.read()StringBuilder(JDK)。 警告:此解决方案存在Unicode问题,例如使用俄语文本(仅适用于非Unicode文本)


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



警告:



  1. 解决方案4,5和9将不同的换行符转换为1。

  2. 解决方案11无法正确使用Unicode文本



性能测试


String(长度= 175)的性能测试,github中的url(模式=平均时间,系统= Linux,得分1,343是最好的):[120]


              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


String(长度= 50100)的性能测试,github中的url(模式=平均时间,系统= Linux,得分200,715是最好的):[121]


               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


图表(性能测试取决于Windows 7系统中的输入流长度)

[122]


性能测试(平均时间)取决于Windows 7系统中的输入流长度:


 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

其它参考3


Apache Commons允许:


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


当然,您可以选择除UTF-8之外的其他字符编码。


另见:(文件)[123]

其它参考4


考虑到文件一应首先获得java.io.Reader实例。然后可以将其读取并添加到StringBuilder(如果我们不在多个线程中访问它,我们就不需要StringBuffer,并且StringBuilder更快)。这里的诀窍是我们在街区工作,因此不需要其他缓冲流。块大小参数化以用于运行时性能优化。


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();
}

其它参考5


这个怎么样?


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();

其它参考6


如果您使用的是Google-Collections/Guava,则可以执行以下操作:


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


请注意,InputStreamReader的第二个参数(即Charsets.UTF_8)是不必要的,但如果你知道它(你应该这样做),通常最好指定编码!

其它参考7


这是我纯粹的Java& Android解决方案,效果很好......


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;
}

其它参考8


怎么样:


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();
}

其它参考9


这是我在经过一些实验后想出的最优雅,最纯粹的Java(无库)解决方案:


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();
}

其它参考10


为了完整起见, Java 9 解决方案:


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


readAllBytes目前在JDK 9主代码库中,因此可能会出现在发行版中。您现在可以使用JDK 9快照构建来尝试它。[124] [125]

其它参考11


我会使用一些Java 8技巧。


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.
    }
}


基本上和其他一些答案一样,除了更简洁。

其它参考12


我经常进行一些计时测试,因为时间很重要


我试图以不同的方式将响应变为String 3。 (如下所示)

为了便于阅读,我省略了try/catch块


为了给出上下文,这是所有3种方法的前面的代码:



   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();


因此,在使用相同的请求/响应数据对每个方法运行500次测试之后,这里是数字。再一次,这些是我的发现,你的发现可能不完全相同,但我写这篇文章是为了向其他人说明这些方法的效率差异。


排名:

方法#1

方法#3 - 比#1低2.6%
方法#2 - 比#1低4.3%


这些方法中的任何一种都是用于获取响应并从中创建String的适当解决方案。

其它参考13


使用Streams的纯Java解决方案,自Java 8开始工作。[126]




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()));
    }
}


正如ChristofferHammarström在其他答案中所提到的,明确指定Charset更安全。即InputStreamReader构造函数可以更改如下: [128]




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

其它参考14


我在这里做了14个不同答案的基准测试(很抱歉没有提供学分但有太多重复)


结果非常令人惊讶。事实证明,Apache IOUtils 是最慢的,ByteArrayOutputStream是最快的解决方案:


所以首先这里是最好的方法:


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);
    }
}


基准测试结果,20个周期内20MB随机字节



时间(以毫秒为单位)



  • ByteArrayOutputStreamTest:194

  • NioStream:198

  • Java9ISTransferTo:201

  • Java9ISReadAllBytes:205

  • BufferedInputStreamVsByteArrayOutputStream:314

  • ApacheStringWriter2:574

  • GuavaCharStreams:589

  • ScannerReaderNoNextTest:614

  • ScannerReader:633

  • ApacheStringWriter:1544

  • StreamApi:错误

  • ParallelStreamApi:错误

  • BufferReaderTest:错误

  • InputStreamAndStringBuilder:错误



基准源代码



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);
        }
    }

}

其它参考15


在这里,或多或少的sampath的答案,清理了一点,并表示为一个功能:


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();
}

其它参考16


如果您喜欢冒险,可以将Scala和Java混合使用,最后得到:


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


混合Java和Scala代码和库有它的好处。


请参阅此处的完整描述:在Scala中将InputStream转换为String的惯用方法

其它参考17


如果你不能在这里使用Commons IO(FileUtils/IOUtils/CopyUtils)这是一个使用BufferedReader逐行读取文件的例子:


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);
    }
}


或者如果你想要原始速度我会建议Paul de Vrieze建议的变体(这避免使用StringWriter(在内部使用StringBuffer):


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);
    }
}

其它参考18


这是一个改编自org.apache.commons.io.IOUtils源代码的答案,适用于那些想要实现apache但不想要整个库的人。[130]


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();
}

其它参考19


如果使用Stream Readers,请务必在结尾处关闭流


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();
}





编辑:在JDK 7+上,您可以使用try-with-resources构造。


/**
 * 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();
    }
}

其它参考20


这是在不使用任何第三方库的情况下将InputStream转换为String的完整方法。将StringBuilder用于单线程环境,否则使用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();
}

其它参考21


这里是如何使用JDK使用字节数组缓冲区来实现的。这实际上是commons-io IOUtils.copy()方法的工作方式。如果你这样做,可以用char[]替换byte[]。从Reader而不是InputStream重新复制。


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);

其它参考22


Kotlin用户只需:


println(InputStreamReader(is).readText())





readText()


是Kotlin标准库的内置扩展方法。

其它参考23


另一个,适用于所有Spring用户:


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);
}


org.springframework.util.StreamUtils中的实用方法类似于FileCopyUtils中的实用方法,但它们在完成后会使流保持打开状态。

其它参考24


使用Java 9中支持的java.io.InputStream.transferTo(OutputStream)和采用charset名称的ByteArrayOutputStream.toString(String):[131] [132]


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

其它参考25


这个很好,因为:



  • Charset的手部安全。

  • 您可以控制读取缓冲区大小。

  • 您可以设置构建器的长度,但可能不完全相同。

  • 没有库依赖项。

  • 适用于Java 7或更高版本。



是为了什么?


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();
}

其它参考26


这是我的基于Java 8 的解决方案,它使用新的Stream API 来收集来自InputStream的所有行:


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

其它参考27


JDK中最简单的方法是使用以下代码snipplet。


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

其它参考28


当输入流来自类路径资源(这似乎是流行的任务)时,Guava提供了更短的高效自动闭合解决方案:[133]


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


要么


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


ByteSource和CharSource也有一般概念,可以轻轻地打开和关闭流。[134] [135]


因此,例如,而不是显式打开一个小文件来读取其内容:


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


要不就


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

其它参考29


以下代码对我有用。


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);


请注意,根据Java文档,available()方法可能不适用于InputStream,但始终与BufferedInputStream一起使用。
如果您不想使用available()方法,我们总是可以使用以下代码


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);


我不确定是否会有任何编码问题。如果代码有任何问题,请发表评论。