11种将InputStream转换成String的方法以及性能分析
作者：Viacheslav Vedenin
原文链接：Read/convert an InputStream to a String
从其他回答中总结出了11种能将InputStream转换成String的方法（如下），并且对所有方法进行了性能测试（对比结果如下）：
将InputStream转换成String的方法：
1.使用 IOUtils.toString (Apache Utils)
String result = IOUtils.toString(inputStream, StandardCharsets.UTF_8);
2.使用 CharStreams (guava)
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)
String result = new BufferedReader(new InputStreamReader(inputStream)) .lines().collect(Collectors.joining("\n"));
5.使用 parallel Stream Api (Java 8)
String result = new BufferedReader(new InputStreamReader(inputStream)).lines() .parallel().collect(Collectors.joining("\n"));
6.使用 InputStreamReader 和 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.使用 StringWriter 和 IOUtils.copy (Apache Commons)
StringWriter writer = new StringWriter(); IOUtils.copy(inputStream, writer, "UTF-8"); return writer.toString();
8.使用 ByteArrayOutputStream 和 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); } return result.toString("UTF-8");
9.使用 BufferedReader (JDK)
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 BufferedInputStream 和 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(); } return buf.toString();
11.使用 inputStream.read() 和 StringBuilder (JDK)
int ch; StringBuilder sb = new StringBuilder(); while((ch = inputStream.read()) != -1) sb.append((char)ch); reset(); return sb.toString();
注意：
1.方法4、5和9会将不同的换行符（例如：\r\n）全转换成\n。
2.方法11在Unicode编码下不能正确地运行。
性能测试
1.针对较短String的性能测试（长度为175）如下所示，代码贴在了github上（模式是测试平均时间，系统是Linux，其中最好的分数是1,343 ）
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
2.针对较长String的性能测试（长度为50100）如下所示，代码贴在了github上（模式是测试平均时间，系统是Linux，其中最好的分数是200,715 ）
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
3.性能测试图（下图主要描述了在Windows7系统下，随着Input Stream长度变化各个方法平均时间的变化） 
4.性能测试数据（同样是在Windows7系统下，随着Input Stream长度变化各个方法平均时间的变化）
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
