java xml转义方法以及中文字符的处理
Posted 秋风兮月
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对于xml的转义最方便,最简单的方法就是直接使用apache的commons.lang jar包中的StringEscapeUtils的escapeXml方法。但该方法在commons lang 2.x和commons lang 3.x的处理方式不太一样。
在commons lang 2.x中StringEscapeUtils的escapeXml方法除了会对xml中的“,&,<,>和‘等字符进行转义外,还会对unicode编码大于0x7F的字符进行转义。
在StringEscapeUtils中创建了xml Entities对象。在该对象中添加了了BASIC_ARRAY和APOS_ARRAY中定义的字符,如果碰到这些字符就会进行转义。
BASIC_ARRAY中定义了
private static final String[][] BASIC_ARRAY = "quot", "34", // " - double-quote
"amp", "38", // & - ampersand
"lt", "60", // < - less-than
"gt", "62", // > - greater-than
;
APOS_ARRAY中定义了
private static final String[][] APOS_ARRAY = "apos", "39", // XML apostrophe
;
因此会对这些定义的字符进行转义。escapeXml方法调用Entities.XML.escape的方法进行转义的具体操作
public void escape(Writer writer, String str) throws IOException
int len = str.length();
for (int i = 0; i < len; i++)
char c = str.charAt(i);
String entityName = this.entityName(c);
if (entityName == null)
if (c > 0x7F)
writer.write("&#");
writer.write(Integer.toString(c, 10));
writer.write(';');
else
writer.write(c);
else
writer.write('&');
writer.write(entityName);
writer.write(';');
可以看出还对Unicode编码大于ox7F的字符进行了转义。因此使用该方法会使得中文字符也会被转义。
如果不想使用中文字符被转义,要么自己可以参考上面的代码,自己改写,去掉对大于0x7F的字符的转义,要么可以使用commons lang3中的escapeXml相关方法。commons lang3中对方法使用策略模式进行了重新设计。相关的方法有escapeXml、escapeXml10和escapeXml11。
其中escapeXml方法已经被废弃。该方法只转义xml中的“,&,<,>和‘5个字符进行转义。将new LookupTranslator(EntityArrays.BASIC_ESCAPE())和new LookupTranslator(EntityArrays.APOS_ESCAPE())两个Tranlator注册到ESCAPE_XML上
escapeXml10方法除了对上述5个字符进行转义外,还会将一些控制字符,例如\\b、\\t、\\n、\\r等等替换成空字符串。因为XML1.0是纯文本格式,不能表示控制字符。另外对于不成对的代理码点也不能表示,因此会去除掉。因此注册到escapeXml10的Translator除了new LookupTranslator(EntityArrays.BASIC_ESCAPE())和new LookupTranslator(EntityArrays.APOS_ESCAPE())外,还有
new LookupTranslator(
new String[][]
"\\u0000", "" , "\\u0001", "" , "\\u0002", "" , "\\u0003", "" , "\\u0004", "" , "\\u0005", "" , "\\u0006", "" , "\\u0007", "" , "\\u0008", "" ,
"\\u000b", "" , "\\u000c", "" , "\\u000e", "" , "\\u000f", "" , "\\u0010", "" , "\\u0011", "" , "\\u0012", "" , "\\u0013", "" , "\\u0014", "" ,
"\\u0015", "" , "\\u0016", "" , "\\u0017", "" , "\\u0018", "" , "\\u0019", "" , "\\u001a", "" , "\\u001b", "" , "\\u001c", "" , "\\u001d", "" ,
"\\u001e", "" , "\\u001f", "" , "\\ufffe", "" , "\\uffff", ""
),
和
new UnicodeUnpairedSurrogateRemover()。
一个是用来处理控制字符,一个是用来处理未成对的代理码点,移除掉码值在[#xD8000,#xDFFF]之间的码值字符。也就是escapeXml10会移除不在下面码值范围内的所有码值:
#x9 | #xA | #xD | [#x20-#xD7FF] | [#xE000-#xFFFD] | [#x10000-#x10FFFF]。
另外escapeXml10还注册了NumericEntityEscaper.between(0x7f, 0x84)和NumericEntityEscaper.between(0x86, 0x9f)两个Translator,将[#x7F-#x84] | [#x86-#x9F]两个范围内的字符进行转义。
对于escapeXml11,由于XML 1.1可以表示一定的控制字符,所以对于控制字符的Translator和escapeXml10不太相同。
new LookupTranslator(
new String[][]
"\\u0000", "" ,
"\\u000b", "" ,
"\\u000c", "" ,
"\\ufffe", "" ,
"\\uffff", ""
)
escapeXml11将会移除不在下面码值范围内的所有码值:
[#x1-#xD7FF] | [#xE000-#xFFFD] | [#x10000-#x10FFFF]
escapeXml11还注册了
NumericEntityEscaper.between(0x1, 0x8),
NumericEntityEscaper.between(0xe, 0x1f),
NumericEntityEscaper.between(0x7f, 0x84),
NumericEntityEscaper.between(0x86, 0x9f),
四个Translator,这样将会对在#x1-#x8] | [#xB-#xC] | [#xE-#x1F] | [#x7F-#x84] | [#x86-#x9F]范围内的码值进行转义。
所使用的主要函数就是这三个。下面说一下其大概的一个工作原理。
对于这三个函数都分别使用了不同的Translator。不过都是AggregateTranslator类的对象。从这个类的名字也可以看出这是个集成Translator,作用就是调用其中注册的一组Translator。所有的Translator都继承自CharSequenceTranslator抽象类,在转义方法中都是直接调用了CharSequenceTranslator的
/**
* Helper for non-Writer usage.
* @param input CharSequence to be translated
* @return String output of translation
*/
public final String translate(final CharSequence input)
if (input == null)
return null;
try
final StringWriter writer = new StringWriter(input.length() * 2);
translate(input, writer);
return writer.toString();
catch (final IOException ioe)
// this should never ever happen while writing to a StringWriter
throw new RuntimeException(ioe);
方法,这个方法又调用了
/**
* Translate an input onto a Writer. This is intentionally final as its algorithm is
* tightly coupled with the abstract method of this class.
*
* @param input CharSequence that is being translated
* @param out Writer to translate the text to
* @throws IOException if and only if the Writer produces an IOException
*/
public final void translate(final CharSequence input, final Writer out) throws IOException
if (out == null)
throw new IllegalArgumentException("The Writer must not be null");
if (input == null)
return;
int pos = 0;
final int len = input.length();
while (pos < len)
//从pos位置开始,对该位置开始的字符进行遍历转义,并返回转义的代码点的个数。注意是代码点,而不是char的个数或者代码单元的个数,
//这个函数在CharSequenceTranslator是个虚函数,需要各继承类实现。并约定每个继承类需要处理码值代理对
//关于码值代理对的概念,可以参考我的另一篇博文“java char String中涉及到的length字符长度概念的研究”
final int consumed = translate(input, pos, out);
if (consumed == 0) //说明调用的traslator没有需要处理的转移字符
// inlined implementation of Character.toChars(Character.codePointAt(input, pos))
// avoids allocating temp char arrays and duplicate checks
char c1 = input.charAt(pos);
out.write(c1);
pos++;
//如果当前位置是个代理对码值,那么就需要把该辅助字符的第一和第二部分同时处理输出
if (Character.isHighSurrogate(c1) && pos < len)
char c2 = input.charAt(pos);
if (Character.isLowSurrogate(c2))
out.write(c2);
pos++;
continue;
// contract with translators is that they have to understand codepoints
// and they just took care of a surrogate pair
//consumed应该表示的是代码点的数量,因此需要获取当前位置的代码点的代码单元的个数,然后将pos指向需要处理的下一个代码点
for (int pt = 0; pt < consumed; pt++)
pos += Character.charCount(Character.codePointAt(input, pos));
该方法又调用了方法
/**
* Translate a set of codepoints, represented by an int index into a CharSequence,
* into another set of codepoints. The number of codepoints consumed must be returned,
* and the only IOExceptions thrown must be from interacting with the Writer so that
* the top level API may reliably ignore StringWriter IOExceptions.
*
* @param input CharSequence that is being translated
* @param index int representing the current point of translation
* @param out Writer to translate the text to
* @return int count of codepoints consumed
* @throws IOException if and only if the Writer produces an IOException
*/
public abstract int translate(CharSequence input, int index, Writer out) throws IOException;
这是个虚函数,继承该类都需要实现。在AggregateTranslator的translate方法中就能直接调用集成在这里面的其它对象的translate方法。
AggregateTranslator的translate方法如下:
/**
* The first translator to consume codepoints from the input is the 'winner'.
* Execution stops with the number of consumed codepoints being returned.
* @inheritDoc
*/
@Override
public int translate(final CharSequence input, final int index, final Writer out) throws IOException
for (final CharSequenceTranslator translator : translators)
final int consumed = translator.translate(input, index, out);
if(consumed != 0)
return consumed;
return 0;
此外,再看一下用的比较频繁的LookupTranslator的实现。
该类的构造函数对传进来的字符映射表进行遍历处理,将二元数组的映射表转换成map保存在lookupMap结构中,便于后续的查找处理,找出每个映射组的前缀保存在prefxSet中。并记录每个二元数组中字符长度最长的和最短的保存在longest和shortest变量中。
其继承实现的translate函数如下:
@Override
public int translate(final CharSequence input, final int index, final Writer out) throws IOException
//从 input的index位置进行比较,只要找到一个就返回
// check if translation exists for the input at position index
if (prefixSet.contains(input.charAt(index)))
int max = longest;
if (index + longest > input.length())
max = input.length() - index;
//先从最长的字符串进行匹配
// implement greedy algorithm by trying maximum match first
for (int i = max; i >= shortest; i--)
final CharSequence subSeq = input.subSequence(index, index + i);
final String result = lookupMap.get(subSeq.toString());
if (result != null)
out.write(result);
return i;
return 0;
具体实现就是这样子的。但是我认为此函数有问题。因为它返回的是char的length而不是代码点的长度。如果lookupTable中的key是含有辅助字符的,在CharSequenceTranslator的tanslate函数处理地方:
// contract with translators is that they have to understand codepoints
// and they just took care of a surrogate pair
for (int pt = 0; pt < consumed; pt++)
pos += Character.charCount(Character.codePointAt(input, pos));
应该就会有bug了。这里需要注意一下。
好了,现在对于escapeXml相关函数的工作原理了解清楚了。其实质就是创建CharSequenceTranslator,调用translate函数进行转义。其实我们也可以根据自己的需要组合出自己的CharSequenceTranslator来进行转义,而不调用定制的escapeXml函数。
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