11种将InputStream转换成String的方法以及性能分析

Love The Way You Lie 2023-07-13 10:49 27阅读 0赞

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)

**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][github 1]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）

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lhbmd5YW5neWU_size_16_color_FFFFFF_t_70][]

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

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另外

在Java中InputStream和String之间的转化十分普遍，本文主要是总结一下转换的各种方法，包括JDK原生提供的，还有一些外部依赖提供的。

1、InputStream转化为String  
1.1 JDK原生提供  
方法一：  
byte\[\] bytes = new byte\[0\];  
bytes = new byte\[inputStream.available()\];  
inputStream.read(bytes);  
String str = new String(bytes);  
  
方法二：  
String result = new BufferedReader(new InputStreamReader(inputStream))  
        .lines().collect(Collectors.joining(System.lineSeparator()));  
  
方法三：  
String result = new BufferedReader(new InputStreamReader(inputStream))  
       .lines().parallel().collect(Collectors.joining(System.lineSeparator()));  
  
方法四：  
Scanner s = new Scanner(inputStream).useDelimiter("\\\\A");  
String str = s.hasNext() ? s.next() : "";  
  
方法五：  
String resource = new Scanner(inputStream).useDelimiter("\\\\Z").next();  
return resource;  
  
方法六：  
StringBuilder sb = new StringBuilder();  
String line;

BufferedReader br = new BufferedReader(new InputStreamReader(inputStream));  
while ((line = br.readLine()) != null) \{  
    sb.append(line);  
\}  
String str = sb.toString();  
return str;  
  
方法七：  
ByteArrayOutputStream result = new ByteArrayOutputStream();  
byte\[\] buffer = new byte\[1024\];  
int length;  
while ((length = inputStream.read(buffer)) != -1) \{  
    result.write(buffer, 0, length);  
\}  
String str = result.toString(StandardCharsets.UTF\_8.name());  
return str;  
  
方法八：  
BufferedInputStream bis = new BufferedInputStream(inputStream);  
ByteArrayOutputStream buf = new ByteArrayOutputStream();  
int result = bis.read();  
while(result != -1) \{  
    buf.write((byte) result);  
    result = bis.read();  
\}  
String str = buf.toString();  
return str;  
  
1.2 Apache Common提供  
方法九：  
StringWriter writer = new StringWriter();  
IOUtils.copy(inputStream, writer, StandardCharsets.UTF\_8.name());  
String str = writer.toString();  
  
方法十：  
String str = IOUtils.toString(inputStream, "utf-8");  
  
1.3 Google Guava提供  
方法十一：  
String str = CharStreams.toString(new InputStreamReader(inputStream, StandardCharsets.UTF\_8));  
  
方法十二：  
String str = new String(ByteStreams.toByteArray(inputStream));  
  
针对一个2MB的文件的输入流，多次执行测试如下(单位是毫秒)：

方法十: 111  
方法十一: 236  
方法十二: 36  
方法一: 36  
方法二: 87  
方法三: 66  
方法四: 101  
方法五: 178  
方法六: 40  
方法七: 21  
方法八: 107  
方法九: 31

从上述结果来看，方法七和方法九更好一些，而方法五和方法十一会更差一些。

2、String转化为InputStream  
2.1 JDK原生提供  
InputStream is = new ByteArrayInputStream(str.getBytes());  
  
2.2 Apache Common提供  
InputStream targetStream = IOUtils.toInputStream(str, StandardCharsets.UTF\_8.name());  
  
2.3 Google Guava提供  
InputStream targetStream =  
        new ReaderInputStream(CharSource.wrap(str).openStream(), StandardCharsets.UTF\_8.name());

转自：

[https://blog.csdn.net/WeakFantasy/article/details/52691041][https_blog.csdn.net_WeakFantasy_article_details_52691041]

[https://blog.csdn.net/lmy86263/article/details/60479350][https_blog.csdn.net_lmy86263_article_details_60479350]

[github]: https://github.com/Vedenin/useful-java-links/blob/master/helloworlds/5.0-other-examples/src/main/java/other_examples/ConvertInputStreamToStringBenchmark.java
[github 1]: https://github.com/Vedenin/useful-java-links/blob/master/helloworlds/5.0-other-examples/src/main/java/other_examples/ConvertBigStringToInputStreamBenchmark.java
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lhbmd5YW5neWU_size_16_color_FFFFFF_t_70]: https://img-blog.csdnimg.cn/20200311172540194.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lhbmd5YW5neWU=,size_16,color_FFFFFF,t_70
[https_blog.csdn.net_WeakFantasy_article_details_52691041]: https://blog.csdn.net/WeakFantasy/article/details/52691041
[https_blog.csdn.net_lmy86263_article_details_60479350]: https://blog.csdn.net/lmy86263/article/details/60479350