Class XmlStreamReader

java.lang.Object
java.io.Reader
org.apache.commons.io.input.XmlStreamReader
All Implemented Interfaces:
Closeable, AutoCloseable, Readable

public class XmlStreamReader extends Reader
Character stream that handles all the necessary Voodoo to figure out the charset encoding of the XML document within the stream.

IMPORTANT: This class is not related in any way to the org.xml.sax.XMLReader. This one IS a character stream.

All this has to be done without consuming characters from the stream, if not the XML parser will not recognized the document as a valid XML. This is not 100% true, but it's close enough (UTF-8 BOM is not handled by all parsers right now, XmlStreamReader handles it and things work in all parsers).

The XmlStreamReader class handles the charset encoding of XML documents in Files, raw streams and HTTP streams by offering a wide set of constructors.

By default the charset encoding detection is lenient, the constructor with the lenient flag can be used for a script (following HTTP MIME and XML specifications). All this is nicely explained by Mark Pilgrim in his blog, Determining the character encoding of a feed.

Originally developed for ROME under Apache License 2.0.

Since:
2.0
See Also:
  • Field Details

  • Constructor Details

    • XmlStreamReader

      public XmlStreamReader(File file) throws IOException
      Creates a Reader for a File.

      It looks for the UTF-8 BOM first, if none sniffs the XML prolog charset, if this is also missing defaults to UTF-8.

      It does a lenient charset encoding detection, check the constructor with the lenient parameter for details.

      Parameters:
      file - File to create a Reader from.
      Throws:
      IOException - thrown if there is a problem reading the file.
    • XmlStreamReader

      public XmlStreamReader(InputStream inputStream) throws IOException
      Creates a Reader for a raw InputStream.

      It follows the same logic used for files.

      It does a lenient charset encoding detection, check the constructor with the lenient parameter for details.

      Parameters:
      inputStream - InputStream to create a Reader from.
      Throws:
      IOException - thrown if there is a problem reading the stream.
    • XmlStreamReader

      public XmlStreamReader(InputStream inputStream, boolean lenient) throws IOException
      Creates a Reader for a raw InputStream.

      It follows the same logic used for files.

      If lenient detection is indicated and the detection above fails as per specifications it then attempts the following:

      If the content type was 'text/html' it replaces it with 'text/xml' and tries the detection again.

      Else if the XML prolog had a charset encoding that encoding is used.

      Else if the content type had a charset encoding that encoding is used.

      Else 'UTF-8' is used.

      If lenient detection is indicated an XmlStreamReaderException is never thrown.

      Parameters:
      inputStream - InputStream to create a Reader from.
      lenient - indicates if the charset encoding detection should be relaxed.
      Throws:
      IOException - thrown if there is a problem reading the stream.
      XmlStreamReaderException - thrown if the charset encoding could not be determined according to the specs.
    • XmlStreamReader

      public XmlStreamReader(InputStream inputStream, boolean lenient, String defaultEncoding) throws IOException
      Creates a Reader for a raw InputStream.

      It follows the same logic used for files.

      If lenient detection is indicated and the detection above fails as per specifications it then attempts the following:

      If the content type was 'text/html' it replaces it with 'text/xml' and tries the detection again.

      Else if the XML prolog had a charset encoding that encoding is used.

      Else if the content type had a charset encoding that encoding is used.

      Else 'UTF-8' is used.

      If lenient detection is indicated an XmlStreamReaderException is never thrown.

      Parameters:
      inputStream - InputStream to create a Reader from.
      lenient - indicates if the charset encoding detection should be relaxed.
      defaultEncoding - The default encoding
      Throws:
      IOException - thrown if there is a problem reading the stream.
      XmlStreamReaderException - thrown if the charset encoding could not be determined according to the specs.
    • XmlStreamReader

      public XmlStreamReader(URL url) throws IOException
      Creates a Reader using the InputStream of a URL.

      If the URL is not of type HTTP and there is not 'content-type' header in the fetched data it uses the same logic used for Files.

      If the URL is a HTTP Url or there is a 'content-type' header in the fetched data it uses the same logic used for an InputStream with content-type.

      It does a lenient charset encoding detection, check the constructor with the lenient parameter for details.

      Parameters:
      url - URL to create a Reader from.
      Throws:
      IOException - thrown if there is a problem reading the stream of the URL.
    • XmlStreamReader

      public XmlStreamReader(URLConnection conn, String defaultEncoding) throws IOException
      Creates a Reader using the InputStream of a URLConnection.

      If the URLConnection is not of type HttpURLConnection and there is not 'content-type' header in the fetched data it uses the same logic used for files.

      If the URLConnection is a HTTP Url or there is a 'content-type' header in the fetched data it uses the same logic used for an InputStream with content-type.

      It does a lenient charset encoding detection, check the constructor with the lenient parameter for details.

      Parameters:
      conn - URLConnection to create a Reader from.
      defaultEncoding - The default encoding
      Throws:
      IOException - thrown if there is a problem reading the stream of the URLConnection.
    • XmlStreamReader

      public XmlStreamReader(InputStream inputStream, String httpContentType) throws IOException
      Creates a Reader using an InputStream and the associated content-type header.

      First it checks if the stream has BOM. If there is not BOM checks the content-type encoding. If there is not content-type encoding checks the XML prolog encoding. If there is not XML prolog encoding uses the default encoding mandated by the content-type MIME type.

      It does a lenient charset encoding detection, check the constructor with the lenient parameter for details.

      Parameters:
      inputStream - InputStream to create the reader from.
      httpContentType - content-type header to use for the resolution of the charset encoding.
      Throws:
      IOException - thrown if there is a problem reading the file.
    • XmlStreamReader

      public XmlStreamReader(InputStream inputStream, String httpContentType, boolean lenient, String defaultEncoding) throws IOException
      Creates a Reader using an InputStream and the associated content-type header. This constructor is lenient regarding the encoding detection.

      First it checks if the stream has BOM. If there is not BOM checks the content-type encoding. If there is not content-type encoding checks the XML prolog encoding. If there is not XML prolog encoding uses the default encoding mandated by the content-type MIME type.

      If lenient detection is indicated and the detection above fails as per specifications it then attempts the following:

      If the content type was 'text/html' it replaces it with 'text/xml' and tries the detection again.

      Else if the XML prolog had a charset encoding that encoding is used.

      Else if the content type had a charset encoding that encoding is used.

      Else 'UTF-8' is used.

      If lenient detection is indicated an XmlStreamReaderException is never thrown.

      Parameters:
      inputStream - InputStream to create the reader from.
      httpContentType - content-type header to use for the resolution of the charset encoding.
      lenient - indicates if the charset encoding detection should be relaxed.
      defaultEncoding - The default encoding
      Throws:
      IOException - thrown if there is a problem reading the file.
      XmlStreamReaderException - thrown if the charset encoding could not be determined according to the specs.
    • XmlStreamReader

      public XmlStreamReader(InputStream inputStream, String httpContentType, boolean lenient) throws IOException
      Creates a Reader using an InputStream and the associated content-type header. This constructor is lenient regarding the encoding detection.

      First it checks if the stream has BOM. If there is not BOM checks the content-type encoding. If there is not content-type encoding checks the XML prolog encoding. If there is not XML prolog encoding uses the default encoding mandated by the content-type MIME type.

      If lenient detection is indicated and the detection above fails as per specifications it then attempts the following:

      If the content type was 'text/html' it replaces it with 'text/xml' and tries the detection again.

      Else if the XML prolog had a charset encoding that encoding is used.

      Else if the content type had a charset encoding that encoding is used.

      Else 'UTF-8' is used.

      If lenient detection is indicated an XmlStreamReaderException is never thrown.

      Parameters:
      inputStream - InputStream to create the reader from.
      httpContentType - content-type header to use for the resolution of the charset encoding.
      lenient - indicates if the charset encoding detection should be relaxed.
      Throws:
      IOException - thrown if there is a problem reading the file.
      XmlStreamReaderException - thrown if the charset encoding could not be determined according to the specs.
  • Method Details

    • getDefaultEncoding

      public String getDefaultEncoding()
      Returns the default encoding to use if none is set in HTTP content-type, XML prolog and the rules based on content-type are not adequate.

      If it is NULL the content-type based rules are used.

      Returns:
      the default encoding to use.
    • getEncoding

      public String getEncoding()
      Returns the charset encoding of the XmlStreamReader.
      Returns:
      charset encoding.
    • read

      public int read(char[] buf, int offset, int len) throws IOException
      Invokes the underlying reader's read(char[], int, int) method.
      Specified by:
      read in class Reader
      Parameters:
      buf - the buffer to read the characters into
      offset - The start offset
      len - The number of bytes to read
      Returns:
      the number of characters read or -1 if the end of stream
      Throws:
      IOException - if an I/O error occurs
    • close

      public void close() throws IOException
      Closes the XmlStreamReader stream.
      Specified by:
      close in interface AutoCloseable
      Specified by:
      close in interface Closeable
      Specified by:
      close in class Reader
      Throws:
      IOException - thrown if there was a problem closing the stream.
    • doRawStream

      private String doRawStream(BOMInputStream bom, BOMInputStream pis, boolean lenient) throws IOException
      Process the raw stream.
      Parameters:
      bom - BOMInputStream to detect byte order marks
      pis - BOMInputStream to guess XML encoding
      lenient - indicates if the charset encoding detection should be relaxed.
      Returns:
      the encoding to be used
      Throws:
      IOException - thrown if there is a problem reading the stream.
    • processHttpStream

      private String processHttpStream(BOMInputStream bom, BOMInputStream pis, String httpContentType, boolean lenient) throws IOException
      Process a HTTP stream.
      Parameters:
      bom - BOMInputStream to detect byte order marks
      pis - BOMInputStream to guess XML encoding
      httpContentType - The HTTP content type
      lenient - indicates if the charset encoding detection should be relaxed.
      Returns:
      the encoding to be used
      Throws:
      IOException - thrown if there is a problem reading the stream.
    • doLenientDetection

      private String doLenientDetection(String httpContentType, XmlStreamReaderException ex) throws IOException
      Do lenient detection.
      Parameters:
      httpContentType - content-type header to use for the resolution of the charset encoding.
      ex - The thrown exception
      Returns:
      the encoding
      Throws:
      IOException - thrown if there is a problem reading the stream.
    • calculateRawEncoding

      String calculateRawEncoding(String bomEnc, String xmlGuessEnc, String xmlEnc) throws IOException
      Calculate the raw encoding.
      Parameters:
      bomEnc - BOM encoding
      xmlGuessEnc - XML Guess encoding
      xmlEnc - XML encoding
      Returns:
      the raw encoding
      Throws:
      IOException - thrown if there is a problem reading the stream.
    • calculateHttpEncoding

      String calculateHttpEncoding(String httpContentType, String bomEnc, String xmlGuessEnc, String xmlEnc, boolean lenient) throws IOException
      Calculate the HTTP encoding.
      Parameters:
      httpContentType - The HTTP content type
      bomEnc - BOM encoding
      xmlGuessEnc - XML Guess encoding
      xmlEnc - XML encoding
      lenient - indicates if the charset encoding detection should be relaxed.
      Returns:
      the HTTP encoding
      Throws:
      IOException - thrown if there is a problem reading the stream.
    • getContentTypeMime

      static String getContentTypeMime(String httpContentType)
      Returns MIME type or NULL if httpContentType is NULL.
      Parameters:
      httpContentType - the HTTP content type
      Returns:
      The mime content type
    • getContentTypeEncoding

      static String getContentTypeEncoding(String httpContentType)
      Returns charset parameter value, NULL if not present, NULL if httpContentType is NULL.
      Parameters:
      httpContentType - the HTTP content type
      Returns:
      The content type encoding (upcased)
    • getXmlProlog

      private static String getXmlProlog(InputStream inputStream, String guessedEnc) throws IOException
      Returns the encoding declared in the <?xml encoding=...?>, NULL if none.
      Parameters:
      inputStream - InputStream to create the reader from.
      guessedEnc - guessed encoding
      Returns:
      the encoding declared in the <?xml encoding=...?>
      Throws:
      IOException - thrown if there is a problem reading the stream.
    • isAppXml

      static boolean isAppXml(String mime)
      Indicates if the MIME type belongs to the APPLICATION XML family.
      Parameters:
      mime - The mime type
      Returns:
      true if the mime type belongs to the APPLICATION XML family, otherwise false
    • isTextXml

      static boolean isTextXml(String mime)
      Indicates if the MIME type belongs to the TEXT XML family.
      Parameters:
      mime - The mime type
      Returns:
      true if the mime type belongs to the TEXT XML family, otherwise false