java - 来自 byte[] 和 UTF-8 的字符串在 Android 上与在 Windows JVM 上给出不同的结果

Question

我正在尝试使用以下代码将字节数组转换为 Java 中的字符串:

byte[] myArray = {25, -50, -86, 81, 47, 44, 97, -5, 69, -4, 87, -114, -47, 62, -113, -64, 58, -32, -121, -102, 53, -89, -122, 12, -2, -23, -127, 111, -100, 53, -87, -23, -44, -28, 4, -21, -42, 75, 87, -112, -38, 118, 54, 92, -116, 4, -118, 110, -87, 7, -13, 3, -72, -63, -69, 123, 92, 94, 56, 61, 120, -52, 98, -17, 5, 41, 101, -3, 121, 81, -90, 12, -35, -21, -24, 112, -94, 123, 62, 8, 27, 54, 107, -77, 64, 8, -102, -99, -1, 119, 127, 43, 12, -31, -1, 51, -15, 83, -4, -68, -30, 91, -104, 84, 18, -122, -120, 66, 116, -17, -101, -24, 105, -112, -116, -64, -108, 112, -35, 61, 66, 100, 5, -24, -26, -44, 81, -84}; // Bytes from Byte.MIN_VALUE to Byte.MAX_VALUE
String result = new String(myArray, StandardCharsets.UTF_8);

问题是，如果我在 Windows (JVM 1.8.0_112) 中运行代码，与在我的 android 设备(在 android 5.1 和 6.0 中测试)中运行代码相比，我会得到不同的结果。我正在测试一个长度为 128 的字节数组，在 android 中我得到一个长度为 120 的字符串，而在 Windows 中我得到一个长度为 125 的字符串。我猜它与一些无效的 utf 字节有关-8 个字符，但我根据平台得到不同的结果仍然很奇怪。

如果我将编码更改为 US-ASCII，我会在两个平台上得到与预期相同的结果:

String result = new String(myArray, StandardCharsets.US_ASCII);

编辑:很抱歉造成混淆。我不是每次都随机生成它。我只是说字节没有有意义的 UTF-8 值。这是我用来测试的字节数组:

System.out.println(Arrays.toString(myArray)): [25, -50, -86, 81, 47, 44, 97, -5, 69, -4, 87, -114, -47, 62, -113, -64, 58, -32, -121, -102, 53, -89, -122, 12, -2, -23, -127, 111, -100, 53, -87, -23, -44, -28, 4, -21, -42, 75, 87, -112, -38, 118, 54, 92, -116, 4, -118, 110, -87, 7, -13, 3, -72, -63, -69, 123, 92, 94, 56, 61, 120, -52, 98, -17, 5, 41, 101, -3, 121, 81, -90, 12, -35, -21, -24, 112, -94, 123, 62, 8, 27, 54, 107, -77, 64, 8, -102, -99, -1, 119, 127, 43, 12, -31, -1, 51, -15, 83, -4, -68, -30, 91, -104, 84, 18, -122, -120, 66, 116, -17, -101, -24, 105, -112, -116, -64, -108, 112, -35, 61, 66, 100, 5, -24, -26, -44, 81, -84]

编辑 2: 窗口结果:

System.out.println(String(myArray, StandardCharsets.UTF_8)).length: 125
System.out.println(String(myArray, StandardCharsets.UTF_8)): ΪQ/,a�E�W��>��:���5����o�5������KW��v6\��n�����{\^8=x�b�)e�yQ����p�{6k����w+��3�S���[�T��Bt��i����p�=Bd���Q�
System.out.println(toUnicode(String(myArray, StandardCharsets.UTF_8))): \u0019\u03aa\u0051\u002f\u002c\u0061\ufffd\u0045\ufffd\u0057\ufffd\ufffd\u003e\ufffd\ufffd\u003a\ufffd\ufffd\ufffd\u0035\ufffd\ufffd\u000c\ufffd\ufffd\u006f\ufffd\u0035\ufffd\ufffd\ufffd\ufffd\u0004\ufffd\ufffd\u004b\u0057\ufffd\ufffd\u0076\u0036\u005c\ufffd\u0004\ufffd\u006e\ufffd\u0007\ufffd\u0003\ufffd\ufffd\ufffd\u007b\u005c\u005e\u0038\u003d\u0078\ufffd\u0062\ufffd\u0005\u0029\u0065\ufffd\u0079\u0051\ufffd\u000c\ufffd\ufffd\ufffd\u0070\ufffd\u007b\u003e\u0008\u001b\u0036\u006b\ufffd\u0040\u0008\ufffd\ufffd\ufffd\u0077\u007f\u002b\u000c\ufffd\ufffd\u0033\ufffd\u0053\ufffd\ufffd\ufffd\u005b\ufffd\u0054\u0012\ufffd\ufffd\u0042\u0074\ufffd\ufffd\u0069\ufffd\ufffd\ufffd\ufffd\u0070\ufffd\u003d\u0042\u0064\u0005\ufffd\ufffd\ufffd\u0051\ufffd

安卓结果:

System.out.println(String(myArray, StandardCharsets.UTF_8)).length: 120
System.out.println(String(myArray, StandardCharsets.UTF_8)): ΪQ/,a�E�W��>��:ǚ5����o�5������KW��v6\��n���{{\^8=x�b�)e�yQ����p�{>6k�@���w+�
System.out.println(toUnicode(String(myArray, StandardCharsets.UTF_8))): \u0019\u03aa\u0051\u002f\u002c\u0061\ufffd\u0045\ufffd\u0057\ufffd\ufffd\u003e\ufffd\ufffd\u003a\u01da\u0035\ufffd\ufffd\u000c\ufffd\ufffd\u006f\ufffd\u0035\ufffd\ufffd\ufffd\ufffd\u0004\ufffd\ufffd\u004b\u0057\ufffd\ufffd\u0076\u0036\u005c\ufffd\u0004\ufffd\u006e\ufffd\u0007\ufffd\u0003\ufffd\u007b\u007b\u005c\u005e\u0038\u003d\u0078\ufffd\u0062\ufffd\u0005\u0029\u0065\ufffd\u0079\u0051\ufffd\u000c\ufffd\ufffd\ufffd\u0070\ufffd\u007b\u003e\u0008\u001b\u0036\u006b\ufffd\u0040\u0008\ufffd\ufffd\ufffd\u0077\u007f\u002b\u000c\ufffd\ufffd\u0033\ufffd\u0053\ufffd\ufffd\u005b\ufffd\u0054\u0012\ufffd\ufffd\u0042\u0074\ufffd\ufffd\u0069\ufffd\ufffd\u0014\u0070\ufffd\u003d\u0042\u0064\u0005\ufffd\ufffd\ufffd\u0051\ufffd

编辑 3:添加了正确的 UTF-16 字符串

编辑 4:将代码更改为工作示例

Answer 1

看来，Android 在解释 UTF-8 序列时有点马虎。标准的相关部分在 D92 中 chapter 3, “Conformance” :

Before the Unicode Standard, Version 3.1, the problematic “non-shortest form” byte sequences in UTF-8 were those where BMP characters could be represented in more than one way. These sequences are ill-formed, because they are not allowed by Table 3-7.

您的输入具有这样的“非最短形式”序列，例如-32、-121、-102和-63、-69。虽然 Android 将这些序列中的每一个解释为单个字符，但 Java 正确地拒绝了这些序列并将格式错误的输入的每个字节转换为单个替换字符，从而产生了更长的字符串。

您可以使用解释“Modified UTF-8”的解析器在 Java 中对其进行演示:

byte[][] samples = {
    { -32, -121, -102 },
    { -63, -69 }
};
for(byte[] array: samples) {
    System.out.println("source: "+Arrays.toString(array));
    String string = new String(array, StandardCharsets.UTF_8);
    System.out.println("strictly interpreted: "+string);
    System.out.println("length: "+string.length());
    ByteBuffer bb = ByteBuffer.allocate(array.length+2);
    bb.putShort((short)array.length).put(array);
    ByteArrayInputStream bis = new ByteArrayInputStream(bb.array());
    DataInputStream dis = new DataInputStream(bis);
    string = dis.readUTF();
    System.out.println("sloppily interpreted: "+string);
    System.out.println("length: "+string.length());
    byte[] actual = string.getBytes(StandardCharsets.UTF_8);
    System.out.println("correct sequence: "+Arrays.toString(actual));
    System.out.println();
}

将打印

source: [-32, -121, -102]
strictly interpreted: ���
length: 3
sloppily interpreted: ǚ
length: 1
correct sequence: [-57, -102]

source: [-63, -69]
strictly interpreted: ��
length: 2
sloppily interpreted: {
length: 1
correct sequence: [123]

它还显示了字符的正确“最短形式”序列。