解析XML文件时,无效的XML 字符 (Unicode: 0x7)异常处理

报错信息：

2015-01-29 00:10:22,075  ERROR commonapi.CommonApiAction - errorCode:5000,5000-00；Description:程序异常。Error on line 1 of document  : An invalid XML character (Unicode: 0x19) was found in the CDATA section. Nested exception: An invalid XML character (Unicode: 0x19) was found in the CDATA section.
org.dom4j.DocumentException: Error on line 1 of document  : An invalid XML character (Unicode: 0x19) was found in the CDATA section. Nested exception: An invalid XML character (Unicode: 0x19) was found in the CDATA section.
at org.dom4j.io.SAXReader.read(SAXReader.java:482)
at org.dom4j.DocumentHelper.parseText(DocumentHelper.java:278)
at com.hoodong.engine.commonapi.CommonApiAction.getWapDocsSearchJsonInfo(CommonApiAction.java:1866)
at sun.reflect.GeneratedMethodAccessor43.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)

错误原因：

这些无效的字符在一些文档中作为文档处理器的控制编码（微软选择了那些再0x82到0x95之间的字符作为"smart"标点），这些也被Unicode保留作为控制编码的，并且在XML中是不合法的。这里的无效字符不是指<,>等不能出现在XML文件的标签以外的字符，也不是由于编码问题引起的乱码，而是一些超出XML合法字符范围的不可见字符。根据W3C标准，有一些字符不能出现在XML文件中：

// Document authors are encouraged to avoid "compatibility characters", as defined in 
// Unicode [Unicode]. The characters defined in the following ranges are also discouraged. // They are either control characters or permanently undefined Unicode characters:

[#x1-#x8], [#xB-#xC], [#xE-#x1F], [#x7F-#x84], [#x86-#x9F], [#xFDD0-#xFDDF],
[#x1FFFE-#x1FFFF], [#x2FFFE-#x2FFFF], [#x3FFFE-#x3FFFF],
[#x4FFFE-#x4FFFF], [#x5FFFE-#x5FFFF], [#x6FFFE-#x6FFFF],
[#x7FFFE-#x7FFFF], [#x8FFFE-#x8FFFF], [#x9FFFE-#x9FFFF],
[#xAFFFE-#xAFFFF], [#xBFFFE-#xBFFFF], [#xCFFFE-#xCFFFF],
[#xDFFFE-#xDFFFF], [#xEFFFE-#xEFFFF], [#xFFFFE-#xFFFFF],
[#x10FFFE-#x10FFFF].

解决办法：

为了保证常用XML解析工具能将自己生成的XML文件成功解析，就需要先将文件中的无效字符过滤掉，或在生成XML文件时就对字符的有效性进行判断，抛弃无效字符。

Unicode是国际组织制定的可以容纳世界上所有文字和符号的字符编码方案。目前的Unicode字符分为17组编排，0x0000 至 0x10FFFF，每组称为平面（Plane），而每平面拥有65536个码位，共1114112个。然而目前只用了少数平面。、、都是将数字转换到程序数据的编码方案。

查了一下W3C中对XML 1.0的定义，其Unicode的合法字符范围(16进制)是：

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

方法一：

// 保留合法字符
public String stripNonValidXMLCharacters(String in) {
    StringBuffer out = new StringBuffer(); // Used to hold the output.
    char current; // Used to reference the current character.

    if (in == null || ("".equals(in))) return ""; // vacancy test.
    for (int i = 0; i < in.length(); i++) {
        current = in.charAt(i); // NOTE: No IndexOutOfBoundsException caught here; it should not happen.
        if ((current == 0x9) ||
            (current == 0xA) ||
            (current == 0xD) ||
            ((current >= 0x20) && (current <= 0xD7FF)) ||
            ((current >= 0xE000) && (current <= 0xFFFD)) ||
            ((current >= 0x10000) && (current <= 0x10FFFF)))
            out.append(current);
    }
    return out.toString();
}

方法二：

//过滤非法字符
//注意，以下正则表达式过滤不全面，过滤范围为
//  0x00 - 0x08
//  0x0b - 0x0c
//  0x0e - 0x1f

public static String stripNonValidXMLChars(String str) {
  if (str == null || "".equals(str)) {
    return str;
  }
  return str.replaceAll("[\x00-\x08\x0b-\x0c\x0e-\x1f]", "");
}

参考：；