在Woodstox XML处理器中，无效字符由以下代码分类:

if (c == 0) {
    throw new IOException("Invalid null character in text to output");
}
if (c < ' ' || (c >= 0x7F && c <= 0x9F)) {
    String msg = "Invalid white space character (0x" + Integer.toHexString(c) + ") in text to output";
    if (mXml11) {
        msg += " (can only be output using character entity)";
    }
    throw new IOException(msg);
}
if (c > 0x10FFFF) {
    throw new IOException("Illegal unicode character point (0x" + Integer.toHexString(c) + ") to output; max is 0x10FFFF as per RFC");
}
/*
 * Surrogate pair in non-quotable (not text or attribute value) content, and non-unicode encoding (ISO-8859-x,
 * Ascii)?
 */
if (c >= SURR1_FIRST && c <= SURR2_LAST) {
    throw new IOException("Illegal surrogate pair -- can only be output via character entities, which are not allowed in this content");
}
throw new IOException("Invalid XML character (0x"+Integer.toHexString(c)+") in text to output");

来自这里

对于Java人来说，Apache有一个实用程序类(StringEscapeUtils)，它有一个帮助方法escapeXml，可以用来使用XML实体转义字符串中的字符。

预先声明的字符是:

& < > " '

有关更多信息，请参阅“XML中的特殊字符是什么?”

唯一的非法字符是&，<和>(以及属性中的"或'，这取决于使用哪个字符来分隔属性值:attr="必须使用"这里，' is allowed '和attr='必须使用&apos;在这里，“is allowed”)。

它们是用XML实体转义的，这里你需要&&。

实际上，您应该使用一个工具或库来为您编写XML，并为您抽象这类东西，这样您就不必担心了。

有效字符的列表在XML规范中:

Char       ::=      #x9 | #xA | #xD | [#x20-#xD7FF] | [#xE000-#xFFFD] | [#x10000-#x10FFFF]  /* any Unicode character, excluding the surrogate blocks, FFFE, and FFFF. */

ampersand (&) is escaped to &

double quotes (") are escaped to "

single quotes (') are escaped to ' 

less than (<) is escaped to &lt; 

greater than (>) is escaped to &gt;

在c#中，使用system . security . securyelement.escape或System.Net.WebUtility.HtmlEncode来转义这些非法字符。

string xml = "<node>it's my \"node\" & i like it 0x12 x09 x0A  0x09 0x0A <node>";
string encodedXml1 = System.Security.SecurityElement.Escape(xml);
string encodedXml2= System.Net.WebUtility.HtmlEncode(xml);


encodedXml1
"&lt;node&gt;it&apos;s my &quot;node&quot; &amp; i like it 0x12 x09 x0A  0x09 0x0A &lt;node&gt;"

encodedXml2
"&lt;node&gt;it&#39;s my &quot;node&quot; &amp; i like it 0x12 x09 x0A  0x09 0x0A &lt;node&gt;"