下載xml，刪除bom並編碼utf8

Question

我正在從FTP服務器下載XML。我必須爲我的SAX解析器做好準備。爲此，我需要刪除BOM字節並將其編碼爲UTF-8。但不知何故，它不適用於每個文件。

這裏是我的兩個功能代碼：

public static void copy(File src, File dest){ 

    try { 
     byte[] data = Files.readAllBytes(src.toPath()); 

     writeAsUTF8(dest, skipBom(data)); 

    } catch (IOException e) { 
     e.printStackTrace(); 
    } 
} 


private static void writeAsUTF8(File out, byte[] data){ 

    try { 

     FileOutputStream outStream = new FileOutputStream(out); 
     OutputStreamWriter outUTF = new OutputStreamWriter(outStream,"UTF8"); 

     outUTF.write(new String(data, "UTF8")); 
     //outUTF.write(new String(data)); 
     outUTF.flush(); 
     outStream.close(); 
     outUTF.close(); 
    } 
    catch(Exception ex){ 
     ex.printStackTrace(); 
    } 
} 

    private static byte[] skipBom(byte[] data){ 

    int skipBytes = getBomSize(data); 

    byte[] tmp = new byte[data.length - skipBytes]; 

    for(int x = 0; x < tmp.length; x++){ 
     tmp[x] = data[x + skipBytes]; 
    } 

    return tmp; 
} 

任何想法我做錯了什麼？

Answer 1

爲什麼要刪除BOM字節？你只需要用文件的編碼將文件讀入字符串，然後使用UTF-8編碼將字符串寫入文件。

Answer 2

我找不出你的代碼有什麼問題。我前段時間遇到同樣的問題，我使用下面的代碼來做到這一點。首先，下面的函數讀取跳過第一個字節的文件。當然，如果您確定所有文件都有BOM，這當然是有道理的。

public byte[] load (File inputFile, int lines) throws Exception { 

    try (BufferedReader reader 
     = new BufferedReader(
      new InputStreamReader(
       new FileInputStream(inputFile), "UTF-8"))) 
    { 
     // Discard the Byte Order Mark 
     int firstByte = reader.read(); 

     String line = null; 
     int lineCount = 0; 

     StringBuilder builder = new StringBuilder(); 
     while(lineCount <= lines && (line = reader.readLine()) != null) { 
      lineCount += 1; 
      builder.append(line + "\n"); 
     } 
    } 

    return builder.toString().getBytes(); 
} 

您可以重寫上述函數，以UTF-8將數據寫回另一個文件。我偶爾使用以下方法轉換磁盤上的文件以將其從ISO轉換爲UTF-8：

public static void convertToUTF8 (Path p) throws Exception { 
    Path docPath = p; 
    Path docPathUTF8 = docPath; 

    InputStreamReader in = new InputStreamReader(new FileInputStream(docPath.toFile()), StandardCharsets.ISO_8859_1); 

    CharBuffer cb = CharBuffer.allocate(100 * 1000 * 1000); 
    int c = -1; 

    while ((c = in.read()) != -1) { 
     cb.put((char) c); 
    } 
    in.close(); 

    OutputStreamWriter out = new OutputStreamWriter(new FileOutputStream(docPathUTF8.toFile()), StandardCharsets.UTF_8); 

    char[] x = new char[cb.position()]; 
    System.arraycopy(cb.array(), 0, x, 0, x.length); 

    out.write(x); 
    out.flush(); 
    out.close(); 
} 

Answer 3

簡化。

writeAsUTF8(dest, data); 



try { 
    int BOM_LENGTH = "\uFFFE".getBytes(StandardCharsets.UTF_8); 
    if (!new String(data, 0, BOM_LENGTH).equals("\uFFFE")) { 
     BOM_LENGTH = 0; 
    } 
    FileOutputStream outStream = new FileOutputStream(out); 
    outStream.write(data, BOM_LENGTH, data.length - BOM_LENGTH)); 
    outStream.close(); 
} 
catch(Exception ex){ 
    ex.printStackTrace(); 
} 

這檢查BOM（U + FFFE）是否存在。僅讀出全部作爲字符串將是更簡單的：

String xml = new String(data, StandardCharsets.UTF_8); 
xml = xml.replaceFirst("^\uFFFE", ""); 

使用字符集，而不是字符串編碼參數是指一個異常少捉：UnsupportedEncodingException（一個IOException）。

---

檢測XML編碼：

String xml = new String(data, StandardCharsets.ISO_8859_1); 
String encoding = xml.replaceFirst(
     "(?s)^.*<\\?xml.*encoding=([\"'])([\\w-]+)\\1.*\\?>.*$", 
     "$2"); 

if (encoding.equals(xml)) { 
    encoding = "UTF-8"; 
} 
xml = new String(data, encoding); 
xml = xml.replaceFirst("^\uFFFE", "");