application/xml 和 text/xml的区别

application/xml and text/xml的区别

 经常看到有关xml时提到"application/xml" 和 "text/xml"两种类型， 二者功能一模一样，唯一的区别就是编码格式，text/xml忽略xml头所指定编码格式而默认采用us-ascii编码，而application/xml会根据xml头指定的编码格式来编码：

     XML has two MIME types,application/xml and text/xml . These are often used interchangeably, but there is a subtle difference which is why application/xml is generally recommended over the latter.

     Let me explain why: according to the standard, text/* -MIME types have a us-ascii character set unless otherwise specified in the HTTP headers. This effectively means that any encoding defined in the XML prolog (e.g. <?xml version=”1.0” encoding=”UTF-8”?>) is ignored. This is of course not the expected and desired behaviour.    

     To further complicate matters, most/all browser implementations actually implement nonstandard behaviour for text/xml because they process the encoding as if it were application/xml .    

     So, text/* has encoding issues, and is not implemented by browsers in a standards-compliant manner, which is why using application/* is recommended.

text/xml 和 application/xml的字符集编码问题

关键字: text/xml application/xml

对于Webservice的应用来说，我们通常都是用UTF-8进行网络传输，但也有通过GBK和GB2312传输的情况，但是在我们Webservice的代码实现中，其实是不用关心具体的传输编码的，因为根据RFC2376的定义，Webservice的引擎（axis，cxf，jaxws..）会根据文件传输的ContentType及XML 声明部分定义的编码自动将网络传输过来的内容（字符串）转换成unicode（jvm运行时的字符串都是以unicode形式存在的）。以下是RFC2376的描述：

例子1：

 webservice传输的文件

Content-type: application/xml; charset="utf-16"
  {BOM}<?xml version="1.0"?>

Content-type: application/xml; charset="utf-16"
  {BOM}<?xml version="1.0"?>

XML and MIME processors会按照utf-16编码处理该文件

例子2：

 webservice传输的文件

Content-type: application/xml
   <?xml version='1.0'?>

Content-type: application/xml
   <?xml version='1.0'?>

XML processors会按照utf-8编码处理该文件

例子3：

 webservice传输的文件

Content-type: application/xml
   <?xml version='1.0' encoding="ISO-10646-UCS-4"?>

Content-type: application/xml
   <?xml version='1.0' encoding="ISO-10646-UCS-4"?>

 XML processors会按照UCS-4编码处理该文件
 

例子4：

 webservice传输的文件

Content-type: text/xml
   {BOM}<?xml version="1.0" encoding="utf-16"?>

Content-type: text/xml
   {BOM}<?xml version="1.0" encoding="utf-16"?>

 XML processors会按照us-ascii，而不是utf-16编码处理该文件

参考文档：

http://www.ietf.org/rfc/rfc2376.txt