Stack Overflow上200万阅读量的一个提问:Java中怎么快速把InputStream转化为String

其实我只是偶尔上Stack Overflow,直到看了这个200万次阅读量的提问:
How do I read / convert an InputStream into a String in Java?

我惊呆了!!!

怎么会有这么多人围观。

我第一反应的解决办法是使用Apache commons包的工具类IOUtils,果不其然,第一条回答就是这个。

我的天!居然有2000+的赞!

继续往下看,发现大家的不少的骚操作

使用 CharStreams (Guava)

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

使用 Scanner (JDK)

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

使用 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"));

使用 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"));

使用 InputStreamReader and StringBuilder (JDK)

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

使用 StringWriter and IOUtils.copy (Apache Commons)

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

使用 ByteArrayOutputStream and 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");

使用 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();
boolean flag = false;
for (String line; (line = reader.readLine()) != null; ) {
    result.append(flag? newLine: "").append(line);
    flag = true;
}
return result.toString();

使用 BufferedInputStream and 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");

使用 inputStream.read() and StringBuilder (JDK).

Warning: This solution has problems with Unicode, for example with Russian text (works correctly only with non-Unicode text)

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

甚至,还贴出了微基准测试的结果,果然狠人啊。

对于小字符串(length = 175) 结果如下:
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

对于大字符串(length = 50100) 结果如下:
Performance tests for big String (length = 50100)
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/o

如获宝藏,看来需要时不时的逛逛Stack Overflow了。

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