Question

我有一个带有utf8编码的xml。此文件包含BOM作为文件的开头。所以在解析过程中我遇到了org.xml.sax.SAXParseException：prolog中不允许使用内容。我无法从文件中删除这3个字节。我无法将文件加载到内存中并在此处删除它们（文件很大）。因此，出于性能原因，我正在使用SAX解析器，如果它们在“”标记之前存在，则只想跳过这3个字节。我应该为此继承InputStreamReader吗？

我是java的新手 - 请告诉我正确的方法。

Answer 1

之前已经出现了，当我遇到Stack Overflow时，我发现了the answer。链接的答案使用PushbackInputStream来测试BOM。

Answer 2

我遇到了同样的问题，我用这段代码解决了这个问题：

private static InputStream checkForUtf8BOM(InputStream inputStream) throws IOException {
    PushbackInputStream pushbackInputStream = new PushbackInputStream(new BufferedInputStream(inputStream), 3);
    byte[] bom = new byte[3];
    if (pushbackInputStream.read(bom) != -1) {
        if (!(bom[0] == (byte) 0xEF && bom[1] == (byte) 0xBB && bom[2] == (byte) 0xBF)) {
            pushbackInputStream.unread(bom);
        }
    }
    return pushbackInputStream;
}

Answer 3

private static char[] UTF32BE = { 0x0000, 0xFEFF };
private static char[] UTF32LE = { 0xFFFE, 0x0000 };
private static char[] UTF16BE = { 0xFEFF };
private static char[] UTF16LE = { 0xFFFE };
private static char[] UTF8 = { 0xEFBB, 0xBF };

private static boolean removeBOM(Reader reader, char[] bom) throws Exception {
    int bomLength = bom.length;
    reader.mark(bomLength);
    char[] possibleBOM = new char[bomLength];
    reader.read(possibleBOM);
    for (int x = 0; x < bomLength; x++) {
        if ((int) bom[x] != (int) possibleBOM[x]) {
            reader.reset();
            return false;
        }
    }
    return true;
}

private static void removeBOM(Reader reader) throws Exception {
    if (removeBOM(reader, UTF32BE)) {
        return;
    }
    if (removeBOM(reader, UTF32LE)) {
        return;
    }
    if (removeBOM(reader, UTF16BE)) {
        return;
    }
    if (removeBOM(reader, UTF16LE)) {
        return;
    }
    if (removeBOM(reader, UTF8)) {
        return;
    }
}

用法：

// xml can be read from a file, url or string through a stream
URL url = new URL("some xml url");
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(url.openStream()));
removeBOM(bufferedReader);

为什么org.apache.xerces.parsers.SAXParser不会跳过utf8编码的xml中的BOM？

3 个答案: