转自StackOverflow:
原贴地址：https://stackoverflow.com/questions/309424/how-do-i-read-convert-an-inputstream-into-a-string-in-java
从InputStream 获得 String 应该算是比较常见的问题，方法也很多，我在网上看到了一个问答，回答者总结了11种常用的方法并比较了它们的运行效率：
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)
注意：这种方式会把换行（比如："\r\n"）一律转化为"\n"
String result = new BufferedReader(new InputStreamReader(inputStream))
.lines().collect(Collectors.joining("\n"));
5. 使用 Parallel Stream API (Java 8)
注意： 这种方式会把换行（比如："\r\n"）一律转化为"\n"
String result = new BufferedReader(new InputStreamReader(inputStream)).lines()
.parallel().collect(Collectors.joining("\n"));
6. 使用 InputStreamReader 和 StreamBuilder (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);
}
// StandardCharsets.UTF_8.name() > JDK 7
return result.toString("UTF-8");
9. 使用 BufferedReader
注意：这种方法会把换行(比如："\n\r")转换成 line.separator 然后在不同的操作系统中转换成不同的形式
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();
10. 使用 BufferedInputStream 和 ByteArrayOutputStram (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() 和 StringBuilder (JDK)
注意： 这种方法不能处理unicode (处理不了中文)
int ch;
StringBuilder sb = new StringBuilder();
while((ch = inputStream.read()) != -1)
sb.append((char)ch);
reset();
return sb.toString();
对小的String (长度为175)进行处理，表现：
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
对大的String (长度为50100) 进行处理，表现：
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
对不同长度的String 进行处理，表现：
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
可见，第8 种方法（使用 ByteArrayOutputStream 和 inputStream.read）效率远优于其他10种
而，第3种方法（使用 Scanner）在3种实验中表现都不是很好
