https://blog.csdn.net/weakfantasy/article/details/52691041

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

刻意练习系列

11种将InputStream转换成String的方法

将InputStream转换成String的方法：

性能测试