如果你有一个java.io.InputStream
对象,你应该如何处理该对象并产生一个String
?
假设我有一个InputStream
包含文本数据,并且我想将其转换为a String
,所以例如我可以将其写入日志文件。
采取InputStream
并将其转换为最简单的方法是String
什么?
public String convertStreamToString(InputStream is) {
// ???
}
发布于 2019-05-17 14:17:28
这是一种仅使用标准Java库的方法(请注意,流未关闭,您的里程可能会有所不同)。
static String convertStreamToString(java.io.InputStream is) {
java.util.Scanner s = new java.util.Scanner(is).useDelimiter("\\A");
return s.hasNext() ? s.next() : "";
}
我从“Stupid Scanner tricks”文章中学到了这个技巧。它工作的原因是因为Scanner迭代流中的标记,在这种情况下我们使用“输入边界的开头”(\ A)分隔标记,因此只为流的整个内容提供一个标记。
注意,如果您需要具体了解输入流的编码,可以为Scanner
构造函数提供第二个参数,指示要使用的字符集(例如“UTF-8”)。
帽子小贴士也向Jacob说道,他曾经指着我说过这篇文章。
发布于 2019-05-17 14:23:50
总结其他答案我找到了11种主要方法(见下文)。我写了一些性能测试(见下面的结果):
将InputStream转换为String的方法:
IOUtils.toString
(Apache Utils)
String result = IOUtils.toString(inputStream, StandardCharsets.UTF_8);
CharStreams
(番石榴)
String result = CharStreams.toString(new InputStreamReader( inputStream, Charsets.UTF_8));
Scanner
(JDK)
Scanner s = new Scanner(inputStream).useDelimiter("\\A"); String result = s.hasNext() ? s.next() : "";
\r\n
)转换为\n
。
String result = new BufferedReader(new InputStreamReader(inputStream)) .lines().collect(Collectors.joining("\n"));
\r\n
)转换为\n
。
String result = new BufferedReader(new InputStreamReader(inputStream)).lines() .parallel().collect(Collectors.joining("\n"));
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();
StringWriter
和IOUtils.copy
(Apache Commons)
StringWriter writer = new StringWriter(); IOUtils.copy(inputStream, writer, "UTF-8"); return writer.toString();
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");
BufferedReader
(JDK)。警告:此解决方案将不同的换行符(例如\n\r
)转换为line.separator
系统属性(例如,在Windows中转换为“\ 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();
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(); } // StandardCharsets.UTF_8.name() > JDK 7 return buf.toString("UTF-8");
inputStream.read()
和StringBuilder
(JDK)。警告:此解决方案存在Unicode问题,例如使用俄语文本(仅适用于非Unicode文本)
int ch; StringBuilder sb = new StringBuilder(); while((ch = inputStream.read()) != -1) sb.append((char)ch); reset(); return sb.toString();
警告:
性能测试
github中小String
(长度= 175),url的性能测试(模式=平均时间,系统= Linux,得分1,343是最好的):
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
大String
(长度= 50100)的性能测试,github中的 url (模式=平均时间,系统= Linux,得分200,715是最好的):
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
图表(性能测试取决于Windows 7系统中的输入流长度)
性能测试(平均时间)取决于Windows 7系统中的输入流长度:
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
https://stackoverflow.com/questions/-100009036
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