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

异-8859-1

如果您知道输入流的编码是ISO-8859-1或ASCII，这里有一种非常高效的方法来实现这一点。它（1）避免了StringWriter的内部StringBuffer中存在的不必要的同步，（2）避免了InputStreamReader的开销，（3）最小化了必须复制StringBuilder的内部字符数组的次数。

public static String iso_8859_1(InputStream is) throws IOException {
    StringBuilder chars = new StringBuilder(Math.max(is.available(), 4096));
    byte[] buffer = new byte[4096];
    int n;
    while ((n = is.read(buffer)) != -1) {
        for (int i = 0; i < n; i++) {
            chars.append((char)(buffer[i] & 0xFF));
        }
    }
    return chars.toString();
}

UTF-8型

对于使用UTF-8编码的流，可以使用相同的通用策略：

public static String utf8(InputStream is) throws IOException {
    StringBuilder chars = new StringBuilder(Math.max(is.available(), 4096));
    byte[] buffer = new byte[4096];
    int n;
    int state = 0;
    while ((n = is.read(buffer)) != -1) {
        for (int i = 0; i < n; i++) {
            if ((state = nextStateUtf8(state, buffer[i])) >= 0) {
                chars.appendCodePoint(state);
            } else if (state == -1) { //error
                state = 0;
                chars.append('\uFFFD'); //replacement char
            }
        }
    }
    return chars.toString();
}

其中nextStateUtf8（）函数定义如下：

/**
 * Returns the next UTF-8 state given the next byte of input and the current state.
 * If the input byte is the last byte in a valid UTF-8 byte sequence,
 * the returned state will be the corresponding unicode character (in the range of 0 through 0x10FFFF).
 * Otherwise, a negative integer is returned. A state of -1 is returned whenever an
 * invalid UTF-8 byte sequence is detected.
 */
static int nextStateUtf8(int currentState, byte nextByte) {
    switch (currentState & 0xF0000000) {
        case 0:
            if ((nextByte & 0x80) == 0) { //0 trailing bytes (ASCII)
                return nextByte;
            } else if ((nextByte & 0xE0) == 0xC0) { //1 trailing byte
                if (nextByte == (byte) 0xC0 || nextByte == (byte) 0xC1) { //0xCO & 0xC1 are overlong
                    return -1;
                } else {
                    return nextByte & 0xC000001F;
                }
            } else if ((nextByte & 0xF0) == 0xE0) { //2 trailing bytes
                if (nextByte == (byte) 0xE0) { //possibly overlong
                    return nextByte & 0xA000000F;
                } else if (nextByte == (byte) 0xED) { //possibly surrogate
                    return nextByte & 0xB000000F;
                } else {
                    return nextByte & 0x9000000F;
                }
            } else if ((nextByte & 0xFC) == 0xF0) { //3 trailing bytes
                if (nextByte == (byte) 0xF0) { //possibly overlong
                    return nextByte & 0x80000007;
                } else {
                    return nextByte & 0xE0000007;
                }
            } else if (nextByte == (byte) 0xF4) { //3 trailing bytes, possibly undefined
                return nextByte & 0xD0000007;
            } else {
                return -1;
            }
        case 0xE0000000: //3rd-to-last continuation byte
            return (nextByte & 0xC0) == 0x80 ? currentState << 6 | nextByte & 0x9000003F : -1;
        case 0x80000000: //3rd-to-last continuation byte, check overlong
            return (nextByte & 0xE0) == 0xA0 || (nextByte & 0xF0) == 0x90 ? currentState << 6 | nextByte & 0x9000003F : -1;
        case 0xD0000000: //3rd-to-last continuation byte, check undefined
            return (nextByte & 0xF0) == 0x80 ? currentState << 6 | nextByte & 0x9000003F : -1;
        case 0x90000000: //2nd-to-last continuation byte
            return (nextByte & 0xC0) == 0x80 ? currentState << 6 | nextByte & 0xC000003F : -1;
        case 0xA0000000: //2nd-to-last continuation byte, check overlong
            return (nextByte & 0xE0) == 0xA0 ? currentState << 6 | nextByte & 0xC000003F : -1;
        case 0xB0000000: //2nd-to-last continuation byte, check surrogate
            return (nextByte & 0xE0) == 0x80 ? currentState << 6 | nextByte & 0xC000003F : -1;
        case 0xC0000000: //last continuation byte
            return (nextByte & 0xC0) == 0x80 ? currentState << 6 | nextByte & 0x3F : -1;
        default:
            return -1;
    }
}

自动检测编码

如果您的输入流是使用ASCII、ISO-8859-1或UTF-8编码的，但您不确定是哪一种，我们可以使用与上一种方法类似的方法，但使用额外的编码检测组件在返回字符串之前自动检测编码。

public static String autoDetect(InputStream is) throws IOException {
    StringBuilder chars = new StringBuilder(Math.max(is.available(), 4096));
    byte[] buffer = new byte[4096];
    int n;
    int state = 0;
    boolean ascii = true;
    while ((n = is.read(buffer)) != -1) {
        for (int i = 0; i < n; i++) {
            if ((state = nextStateUtf8(state, buffer[i])) > 0x7F)
                ascii = false;
            chars.append((char)(buffer[i] & 0xFF));
        }
    }

    if (ascii || state < 0) { //probably not UTF-8
        return chars.toString();
    }
    //probably UTF-8
    int pos = 0;
    char[] charBuf = new char[2];
    for (int i = 0, len = chars.length(); i < len; i++) {
        if ((state = nextStateUtf8(state, (byte)chars.charAt(i))) >= 0) {
            boolean hi = Character.toChars(state, charBuf, 0) == 2;
            chars.setCharAt(pos++, charBuf[0]);
            if (hi) {
                chars.setCharAt(pos++, charBuf[1]);
            }
        }
    }
    return chars.substring(0, pos);
}

如果您的输入流的编码既不是ISO-8859-1，也不是ASCII，也不是UTF-8，那么我就遵从已经存在的其他答案。

如果使用流读取器，请确保在结束时关闭流

private String readStream(InputStream iStream) throws IOException {
    //build a Stream Reader, it can read char by char
    InputStreamReader iStreamReader = new InputStreamReader(iStream);
    //build a buffered Reader, so that i can read whole line at once
    BufferedReader bReader = new BufferedReader(iStreamReader);
    String line = null;
    StringBuilder builder = new StringBuilder();
    while((line = bReader.readLine()) != null) {  //Read till end
        builder.append(line);
        builder.append("\n"); // append new line to preserve lines
    }
    bReader.close();         //close all opened stuff
    iStreamReader.close();
    //iStream.close(); //EDIT: Let the creator of the stream close it!
                       // some readers may auto close the inner stream
    return builder.toString();
}

编辑：在JDK7+上，可以使用trywithresources构造。

/**
 * Reads the stream into a string
 * @param iStream the input stream
 * @return the string read from the stream
 * @throws IOException when an IO error occurs
 */
private String readStream(InputStream iStream) throws IOException {

    //Buffered reader allows us to read line by line
    try (BufferedReader bReader =
                 new BufferedReader(new InputStreamReader(iStream))){
        StringBuilder builder = new StringBuilder();
        String line;
        while((line = bReader.readLine()) != null) {  //Read till end
            builder.append(line);
            builder.append("\n"); // append new line to preserve lines
        }
        return builder.toString();
    }
}

以下是我经过一些实验后提出的最优雅、纯Java（无库）解决方案：

public static String fromStream(InputStream in) throws IOException
{
    BufferedReader reader = new BufferedReader(new InputStreamReader(in));
    StringBuilder out = new StringBuilder();
    String newLine = System.getProperty("line.separator");
    String line;
    while ((line = reader.readLine()) != null) {
        out.append(line);
        out.append(newLine);
    }
    return out.toString();
}

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);
}

Use:

import java.io.BufferedInputStream;
import java.io.ByteArrayOutputStream;
import java.io.InputStream;
import java.io.IOException;

public static String readInputStreamAsString(InputStream in)
    throws IOException {

    BufferedInputStream bis = new BufferedInputStream(in);
    ByteArrayOutputStream buf = new ByteArrayOutputStream();
    int result = bis.read();
    while(result != -1) {
      byte b = (byte)result;
      buf.write(b);
      result = bis.read();
    }
    return buf.toString();
}