如果您有java.io.InputStream对象,应该如何处理该对象并生成String?


假设我有一个包含文本数据的InputStream,我想将其转换为String,例如,我可以将其写入日志文件。

获取InputStream并将其转换为字符串的最简单方法是什么?

public String convertStreamToString(InputStream is) {
// ???
}

当前回答

总结我找到的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转换为字符串的方法:

使用IOUtils.toString(Apache Utils)字符串结果=IOTils.toString(inputStream,StandardCharsets.UTF_8);使用CharStreams(Guava)字符串结果=CharStreams.toString(新InputStreamReader(inputStream、字符集UTF_8));使用扫描仪(JDK)扫描仪s=新扫描仪(inputStream)。使用分隔符(“\\A”);字符串结果=s.hasNext()?s.next():“”;使用流API(Java 8)。警告:此解决方案将不同的换行符(如\r\n)转换为\n。字符串结果=新BufferedReader(新InputStreamReader(inputStream)).line().collector(Collectors.joining(“\n”));使用并行流API(Java8)。警告:此解决方案将不同的换行符(如\r\n)转换为\n。字符串结果=新BufferedReader(新InputStreamReader(inputStream)).line().allel().collector(Collectors.joining(“\n”));使用InputStreamReader和StringBuilder(JDK)int bufferSize=1024;char[]缓冲区=新字符[bufferSize];StringBuilder out=新StringBuilder();Reader in=新InputStreamReader(流,StandardCharsets.UTF_8);for(int numRead;(numRead=in.read(buffer,0,buffer.length))>0;){out.append(缓冲区,0,numRead);}return out.toString();使用StringWriter和IOUtils.copy(Apache Commons)StringWriter writer=新StringWriter();IOUtils.copy(inputStream,writer,“UTF-8”);return writer.toString();使用ByteArrayOutputStream和inputStream.read(JDK)ByteArrayOutputStream result=new ByteArrayOutputStream();byte[]缓冲区=新字节[1024];for(int length;(length=inputStream.read(缓冲区))!=-1; ) {result.write(缓冲区,0,长度);}//StandardCharsets.UTF_8.name()>JDK 7return result.toString(“UTF-8”);使用BufferedReader(JDK)。警告:此解决方案将不同的换行符(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.sepaper”);BufferedReader读取器=新的BufferedReader(新的InputStreamReader(inputStream));StringBuilder result=new StringBuilder();for(字符串行;(行=reader.readLine())!=null;){如果(result.length()>0){result.append(换行符);}result.append(行);}return result.toString();使用BufferedInputStream和ByteArrayOutputStream(JDK)BufferedInputStream bis=新缓冲输入流(inputStream);ByteArrayOutputStream buf=新ByteArrayOutputStream();for(int result=bis.read();结果!=-1.result=bis.read()){buf.write((字节)结果);}//StandardCharsets.UTF_8.name()>JDK 7return buf.toString(“UTF-8”);使用inputStream.read()和StringBuilder(JDK)。警告:此解决方案存在Unicode问题,例如俄语文本(仅适用于非Unicode文本)StringBuilder sb=新StringBuilder();for(int ch;(ch=inputStream.read())!=-1; ) {sb.append((char)ch);}return sb.toString();

警告:

解决方案4、5和9将不同的换行符转换为一个。解决方案11无法正确使用Unicode文本

性能测试

小字符串(长度=175)的性能测试,github中的url(模式=平均时间,系统=Linux,分数1343最好):

              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

对大字符串(长度=50100)、github中的url进行性能测试(模式=平均时间,系统=Linux,得分200715最好):

               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

其他回答

最简单的方法,一行:

public static void main(String... args) throws IOException {
    System.out.println(new String(Files.readAllBytes(Paths.get("csv.txt"))));
}

这是最适合Android和任何其他JVM的纯Java解决方案。

这个解决方案非常好。。。它简单、快速,适用于大小河流!!(见上文第8号基准)

public String readFullyAsString(InputStream inputStream, String encoding)
        throws IOException {
    return readFully(inputStream).toString(encoding);
}

public byte[] readFullyAsBytes(InputStream inputStream)
        throws IOException {
    return readFully(inputStream).toByteArray();
}

private ByteArrayOutputStream readFully(InputStream inputStream)
        throws IOException {
    ByteArrayOutputStream baos = new ByteArrayOutputStream();
    byte[] buffer = new byte[1024];
    int length = 0;
    while ((length = inputStream.read(buffer)) != -1) {
        baos.write(buffer, 0, length);
    }
    return baos;
}
InputStreamReader i = new InputStreamReader(s);
BufferedReader str = new BufferedReader(i);
String msg = str.readLine();
System.out.println(msg);

这是您的InputStream对象,它将被转换为String

public String read(InputStream in) throws IOException {
    try (BufferedReader buffer = new BufferedReader(new InputStreamReader(in))) {
        return buffer.lines().collect(Collectors.joining("\n"));
    }
}

此代码段位于\sdk\samples\android-19\connection\NetworkConnect\NetworkConnectSample\src\main\java.com\example\android\NetworkConnect\MainActivity.java中,该代码段根据Apache许可证2.0版授权,由Google编写。

/** Reads an InputStream and converts it to a String.
 * @param stream InputStream containing HTML from targeted site.
 * @param len Length of string that this method returns.
 * @return String concatenated according to len parameter.
 * @throws java.io.IOException
 * @throws java.io.UnsupportedEncodingException
 */
private String readIt(InputStream stream, int len) throws IOException, UnsupportedEncodingException {
    Reader reader = null;
    reader = new InputStreamReader(stream, "UTF-8");
    char[] buffer = new char[len];
    reader.read(buffer);
    return new String(buffer);
}