Java中将InputStream读取为String, 各种方法的性能对比
如下, 一共存在11种实现方式及其对应的性能测试结果:
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). 提醒: 这种方式会将不同的换行符 (比如\r\n) 都替换为 \n.
String result = new BufferedReader(new InputStreamReader(inputStream)) .lines().collect(Collectors.joining("\n"));
5. 使用parallel Stream Api (Java 8). 提醒: 这种方式会将不同的换行符 (比如\r\n) 都替换为 \n.
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). 提醒: 这种方式会将不同的换行符 (比如\r\n) 都替换为当前系统的换行符(例如, 在windows下是"\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). 提醒: 这种方式处理Unicode时存在问题, 例如俄文, 仅在非Unicode字符串下工作正常.
int ch; StringBuilder sb = new StringBuilder(); while((ch = inputStream.read()) != -1) sb.append((char)ch); reset(); return sb.toString();
提醒:
方式 4, 5 和 9 都存在替换换行符的问题. 方式11在Unicode下不能正常工作.
性能测试
对于短字符串 (length = 175)的测试, url in github (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
对于长字符串的测试 (length = 50100), url in github (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/op
可以看出8和6是相对更好的选择
