Module jakarta.mail

Class MimeUtility

java.lang.Object
jakarta.mail.internet.MimeUtility

public class MimeUtility extends Object
This is a utility class that provides various MIME related functionality.

There are a set of methods to encode and decode MIME headers as per RFC 2047. Note that, in general, these methods are not needed when using methods such as setSubject and setRecipients; Jakarta Mail will automatically encode and decode data when using these "higher level" methods. The methods below are only needed when maniuplating raw MIME headers using setHeader and getHeader methods. A brief description on handling such headers is given below:

RFC 822 mail headers must contain only US-ASCII characters. Headers that contain non US-ASCII characters must be encoded so that they contain only US-ASCII characters. Basically, this process involves using either BASE64 or QP to encode certain characters. RFC 2047 describes this in detail.

In Java, Strings contain (16 bit) Unicode characters. ASCII is a subset of Unicode (and occupies the range 0 - 127). A String that contains only ASCII characters is already mail-safe. If the String contains non US-ASCII characters, it must be encoded. An additional complexity in this step is that since Unicode is not yet a widely used charset, one might want to first charset-encode the String into another charset and then do the transfer-encoding.

Note that to get the actual bytes of a mail-safe String (say, for sending over SMTP), one must do


        byte[] bytes = string.getBytes("iso-8859-1");   

 

The setHeader and addHeader methods on MimeMessage and MimeBodyPart assume that the given header values are Unicode strings that contain only US-ASCII characters. Hence the callers of those methods must insure that the values they pass do not contain non US-ASCII characters. The methods in this class help do this.

The getHeader family of methods on MimeMessage and MimeBodyPart return the raw header value. These might be encoded as per RFC 2047, and if so, must be decoded into Unicode Strings. The methods in this class help to do this.

Several System properties control strict conformance to the MIME spec. Note that these are not session properties but must be set globally as System properties.

The mail.mime.decodetext.strict property controls decoding of MIME encoded words. The MIME spec requires that encoded words start at the beginning of a whitespace separated word. Some mailers incorrectly include encoded words in the middle of a word. If the mail.mime.decodetext.strict System property is set to "false", an attempt will be made to decode these illegal encoded words. The default is true.

The mail.mime.encodeeol.strict property controls the choice of Content-Transfer-Encoding for MIME parts that are not of type "text". Often such parts will contain textual data for which an encoding that allows normal end of line conventions is appropriate. In rare cases, such a part will appear to contain entirely textual data, but will require an encoding that preserves CR and LF characters without change. If the mail.mime.encodeeol.strict System property is set to "true", such an encoding will be used when necessary. The default is false.

In addition, the mail.mime.charset System property can be used to specify the default MIME charset to use for encoded words and text parts that don't otherwise specify a charset. Normally, the default MIME charset is derived from the default Java charset, as specified in the file.encoding System property. Most applications will have no need to explicitly set the default MIME charset. In cases where the default MIME charset to be used for mail messages is different than the charset used for files stored on the system, this property should be set.

The current implementation also supports the following System property.

The mail.mime.ignoreunknownencoding property controls whether unknown values in the Content-Transfer-Encoding header, as passed to the decode method, cause an exception. If set to "true", unknown values are ignored and 8bit encoding is assumed. Otherwise, unknown values cause a MessagingException to be thrown.

  • Field Details

    • ALL

      public static final int ALL
      See Also:
    • nonAsciiCharsetMap

      private static final Map<String,Boolean> nonAsciiCharsetMap
    • WORD_SPECIALS

      private static final String WORD_SPECIALS
      See Also:
    • TEXT_SPECIALS

      private static final String TEXT_SPECIALS
      See Also:
    • decodeStrict

      private static final boolean decodeStrict
    • encodeEolStrict

      private static final boolean encodeEolStrict
    • ignoreUnknownEncoding

      private static final boolean ignoreUnknownEncoding
    • allowUtf8

      private static final boolean allowUtf8
    • foldEncodedWords

      private static final boolean foldEncodedWords
    • foldText

      private static final boolean foldText
    • defaultJavaCharset

      private static String defaultJavaCharset
    • defaultMIMECharset

      private static String defaultMIMECharset
    • mime2java

      private static Map<String,String> mime2java
    • java2mime

      private static Map<String,String> java2mime
    • ALL_ASCII

      static final int ALL_ASCII
      See Also:
    • MOSTLY_ASCII

      static final int MOSTLY_ASCII
      See Also:
    • MOSTLY_NONASCII

      static final int MOSTLY_NONASCII
      See Also:
  • Constructor Details

    • MimeUtility

      private MimeUtility()
  • Method Details

    • getEncoding

      public static String getEncoding(jakarta.activation.DataSource ds)
      Get the Content-Transfer-Encoding that should be applied to the input stream of this DataSource, to make it mail-safe.

      The algorithm used here is:

      • If the DataSource implements EncodingAware, ask it what encoding to use. If it returns non-null, return that value.
      • If the primary type of this datasource is "text" and if all the bytes in its input stream are US-ASCII, then the encoding is StreamProvider.BIT7_ENCODER. If more than half of the bytes are non-US-ASCII, then the encoding is StreamProvider.BASE_64_ENCODER. If less than half of the bytes are non-US-ASCII, then the encoding is StreamProvider.QUOTED_PRINTABLE_ENCODER.
      • If the primary type of this datasource is not "text", then if all the bytes of its input stream are US-ASCII, the encoding is StreamProvider.BIT7_ENCODER. If there is even one non-US-ASCII character, the encoding is StreamProvider.BASE_64_ENCODER.
      Parameters:
      ds - the DataSource
      Returns:
      the encoding. This is either StreamProvider.BIT7_ENCODER, StreamProvider.QUOTED_PRINTABLE_ENCODER or StreamProvider.BASE_64_ENCODER
    • nonAsciiCharset

      private static boolean nonAsciiCharset(ContentType ct)
      Determine whether the charset in the Content-Type is compatible with ASCII or not. A charset is compatible with ASCII if the encoded byte stream representing the Unicode string "\r\n" is the ASCII characters CR and LF. For example, the utf-16be charset is not compatible with ASCII. For performance, we keep a static map that caches the results.
    • getEncoding

      public static String getEncoding(jakarta.activation.DataHandler dh)
      Same as getEncoding(DataSource) except that instead of reading the data from an InputStream it uses the writeTo method to examine the data. This is more efficient in the common case of a DataHandler created with an object and a MIME type (for example, a "text/plain" String) because all the I/O is done in this thread. In the case requiring an InputStream the DataHandler uses a thread, a pair of pipe streams, and the writeTo method to produce the data.

      Parameters:
      dh - the DataHandler
      Returns:
      the Content-Transfer-Encoding
      Since:
      JavaMail 1.2
    • decode

      public static InputStream decode(InputStream is, String encoding) throws MessagingException
      Decode the given input stream. The Input stream returned is the decoded input stream. All the encodings defined in RFC 2045 are supported here. They include StreamProvider.BASE_64_ENCODER, StreamProvider.QUOTED_PRINTABLE_ENCODER, StreamProvider.BIT7_ENCODER, StreamProvider.BIT8_ENCODER, and StreamProvider.BINARY_ENCODER. In addition, StreamProvider.UU_ENCODER is also supported.

      In the current implementation, if the mail.mime.ignoreunknownencoding system property is set to "true", unknown encoding values are ignored and the original InputStream is returned.

      Parameters:
      is - input stream
      encoding - the encoding of the stream.
      Returns:
      decoded input stream.
      Throws:
      MessagingException - if the encoding is unknown
    • encode

      public static OutputStream encode(OutputStream os, String encoding) throws MessagingException
      Wrap an encoder around the given output stream. All the encodings defined in RFC 2045 are supported here. They include StreamProvider.BASE_64_ENCODER, StreamProvider.QUOTED_PRINTABLE_ENCODER, StreamProvider.BIT7_ENCODER, StreamProvider.BIT8_ENCODER and StreamProvider.BINARY_ENCODER. In addition, StreamProvider.UU_ENCODER is also supported.
      Parameters:
      os - output stream
      encoding - the encoding of the stream.
      Returns:
      output stream that applies the specified encoding.
      Throws:
      MessagingException - if the encoding is unknown
    • encode

      public static OutputStream encode(OutputStream os, String encoding, String filename) throws MessagingException
      Wrap an encoder around the given output stream. All the encodings defined in RFC 2045 are supported here. They include StreamProvider.BASE_64_ENCODER, StreamProvider.QUOTED_PRINTABLE_ENCODER, StreamProvider.BIT7_ENCODER, StreamProvider.BIT8_ENCODER and StreamProvider.BINARY_ENCODER. In addition, StreamProvider.UU_ENCODER is also supported. The filename parameter is used with the StreamProvider.UU_ENCODER encoding and is included in the encoded output.
      Parameters:
      os - output stream
      encoding - the encoding of the stream.
      filename - name for the file being encoded (only used with uuencode)
      Returns:
      output stream that applies the specified encoding.
      Throws:
      MessagingException - for unknown encodings
      Since:
      JavaMail 1.2
    • encodeText

      public static String encodeText(String text) throws UnsupportedEncodingException
      Encode a RFC 822 "text" token into mail-safe form as per RFC 2047.

      The given Unicode string is examined for non US-ASCII characters. If the string contains only US-ASCII characters, it is returned as-is. If the string contains non US-ASCII characters, it is first character-encoded using the platform's default charset, then transfer-encoded using either the B or Q encoding. The resulting bytes are then returned as a Unicode string containing only ASCII characters.

      Note that this method should be used to encode only "unstructured" RFC 822 headers.

      Example of usage:

      
        MimePart part = ...
        String rawvalue = "FooBar Mailer, Japanese version 1.1"
        try {
          // If we know for sure that rawvalue contains only US-ASCII 
          // characters, we can skip the encoding part
          part.setHeader("X-mailer", MimeUtility.encodeText(rawvalue));
        } catch (UnsupportedEncodingException e) {
          // encoding failure
        } catch (MessagingException me) {
         // setHeader() failure
        }
      
       

      Parameters:
      text - Unicode string
      Returns:
      Unicode string containing only US-ASCII characters
      Throws:
      UnsupportedEncodingException - if the encoding fails
    • encodeText

      public static String encodeText(String text, String charset, String encoding) throws UnsupportedEncodingException
      Encode a RFC 822 "text" token into mail-safe form as per RFC 2047.

      The given Unicode string is examined for non US-ASCII characters. If the string contains only US-ASCII characters, it is returned as-is. If the string contains non US-ASCII characters, it is first character-encoded using the specified charset, then transfer-encoded using either the B or Q encoding. The resulting bytes are then returned as a Unicode string containing only ASCII characters.

      Note that this method should be used to encode only "unstructured" RFC 822 headers.

      Parameters:
      text - the header value
      charset - the charset. If this parameter is null, the platform's default chatset is used.
      encoding - the encoding to be used. Currently supported values are "B" and "Q". If this parameter is null, then the "Q" encoding is used if most of characters to be encoded are in the ASCII charset, otherwise "B" encoding is used.
      Returns:
      Unicode string containing only US-ASCII characters
      Throws:
      UnsupportedEncodingException - if the charset conversion failed.
    • decodeText

      public static String decodeText(String etext) throws UnsupportedEncodingException
      Decode "unstructured" headers, that is, headers that are defined as '*text' as per RFC 822.

      The string is decoded using the algorithm specified in RFC 2047, Section 6.1. If the charset-conversion fails for any sequence, an UnsupportedEncodingException is thrown. If the String is not an RFC 2047 style encoded header, it is returned as-is

      Example of usage:

      
        MimePart part = ...
        String rawvalue = null;
        String  value = null;
        try {
          if ((rawvalue = part.getHeader("X-mailer")[0]) != null)
            value = MimeUtility.decodeText(rawvalue);
        } catch (UnsupportedEncodingException e) {
            // Don't care
            value = rawvalue;
        } catch (MessagingException me) { }
      
        return value;
      
       

      Parameters:
      etext - the possibly encoded value
      Returns:
      the decoded text
      Throws:
      UnsupportedEncodingException - if the charset conversion failed.
    • encodeWord

      public static String encodeWord(String word) throws UnsupportedEncodingException
      Encode a RFC 822 "word" token into mail-safe form as per RFC 2047.

      The given Unicode string is examined for non US-ASCII characters. If the string contains only US-ASCII characters, it is returned as-is. If the string contains non US-ASCII characters, it is first character-encoded using the platform's default charset, then transfer-encoded using either the B or Q encoding. The resulting bytes are then returned as a Unicode string containing only ASCII characters.

      This method is meant to be used when creating RFC 822 "phrases". The InternetAddress class, for example, uses this to encode it's 'phrase' component.

      Parameters:
      word - Unicode string
      Returns:
      Array of Unicode strings containing only US-ASCII characters.
      Throws:
      UnsupportedEncodingException - if the encoding fails
    • encodeWord

      public static String encodeWord(String word, String charset, String encoding) throws UnsupportedEncodingException
      Encode a RFC 822 "word" token into mail-safe form as per RFC 2047.

      The given Unicode string is examined for non US-ASCII characters. If the string contains only US-ASCII characters, it is returned as-is. If the string contains non US-ASCII characters, it is first character-encoded using the specified charset, then transfer-encoded using either the B or Q encoding. The resulting bytes are then returned as a Unicode string containing only ASCII characters.

      Parameters:
      word - Unicode string
      charset - the MIME charset
      encoding - the encoding to be used. Currently supported values are "B" and "Q". If this parameter is null, then the "Q" encoding is used if most of characters to be encoded are in the ASCII charset, otherwise "B" encoding is used.
      Returns:
      Unicode string containing only US-ASCII characters
      Throws:
      UnsupportedEncodingException - if the encoding fails
    • encodeWord

      private static String encodeWord(String string, String charset, String encoding, boolean encodingWord) throws UnsupportedEncodingException
      Throws:
      UnsupportedEncodingException
    • bEncodedLength

      private static int bEncodedLength(byte[] b)
      Returns the length of the encoded version of this byte array.
      Parameters:
      b - the byte array
      Returns:
      the length
    • qEncodedLength

      private static int qEncodedLength(byte[] b, boolean encodingWord)
      Returns the length of the encoded version of this byte array.
      Parameters:
      b - the byte array
      encodingWord - true if encoding words, false if encoding text
      Returns:
      the length
    • doEncode

      private static void doEncode(String string, boolean b64, String jcharset, int avail, String prefix, boolean first, boolean encodingWord, StringBuilder buf) throws UnsupportedEncodingException
      Throws:
      UnsupportedEncodingException
    • decodeWord

      public static String decodeWord(String eword) throws ParseException, UnsupportedEncodingException
      The string is parsed using the rules in RFC 2047 and RFC 2231 for parsing an "encoded-word". If the parse fails, a ParseException is thrown. Otherwise, it is transfer-decoded, and then charset-converted into Unicode. If the charset-conversion fails, an UnsupportedEncodingException is thrown.

      Parameters:
      eword - the encoded value
      Returns:
      the decoded word
      Throws:
      ParseException - if the string is not an encoded-word as per RFC 2047 and RFC 2231.
      UnsupportedEncodingException - if the charset conversion failed.
    • decodeInnerWords

      private static String decodeInnerWords(String word) throws UnsupportedEncodingException
      Look for encoded words within a word. The MIME spec doesn't allow this, but many broken mailers, especially Japanese mailers, produce such incorrect encodings.
      Throws:
      UnsupportedEncodingException
    • quote

      public static String quote(String word, String specials)
      A utility method to quote a word, if the word contains any characters from the specified 'specials' list.

      The HeaderTokenizer class defines two special sets of delimiters - MIME and RFC 822.

      This method is typically used during the generation of RFC 822 and MIME header fields.

      Parameters:
      word - word to be quoted
      specials - the set of special characters
      Returns:
      the possibly quoted word
      See Also:
    • fold

      public static String fold(int used, String s)
      Fold a string at linear whitespace so that each line is no longer than 76 characters, if possible. If there are more than 76 non-whitespace characters consecutively, the string is folded at the first whitespace after that sequence. The parameter used indicates how many characters have been used in the current line; it is usually the length of the header name.

      Note that line breaks in the string aren't escaped; they probably should be.

      Parameters:
      used - characters used in line so far
      s - the string to fold
      Returns:
      the folded string
      Since:
      JavaMail 1.4
    • makesafe

      private static String makesafe(CharSequence s)
      If the String or StringBuilder has any embedded newlines, make sure they're followed by whitespace, to prevent header injection errors.
    • unfold

      public static String unfold(String s)
      Unfold a folded header. Any line breaks that aren't escaped and are followed by whitespace are removed.
      Parameters:
      s - the string to unfold
      Returns:
      the unfolded string
      Since:
      JavaMail 1.4
    • indexOfAny

      private static int indexOfAny(String s, String any)
      Return the first index of any of the characters in "any" in "s", or -1 if none are found. This should be a method on String.
    • indexOfAny

      private static int indexOfAny(String s, String any, int start)
    • javaCharset

      public static String javaCharset(String charset)
      Convert a MIME charset name into a valid Java charset name.

      Parameters:
      charset - the MIME charset name
      Returns:
      the Java charset equivalent. If a suitable mapping is not available, the passed in charset is itself returned.
    • mimeCharset

      public static String mimeCharset(String charset)
      Convert a java charset into its MIME charset name.

      Note that a future version of JDK (post 1.2) might provide this functionality, in which case, we may deprecate this method then.

      Parameters:
      charset - the JDK charset
      Returns:
      the MIME/IANA equivalent. If a mapping is not possible, the passed in charset itself is returned.
      Since:
      JavaMail 1.1
    • getDefaultJavaCharset

      public static String getDefaultJavaCharset()
      Get the default charset corresponding to the system's current default locale. If the System property mail.mime.charset is set, a system charset corresponding to this MIME charset will be returned.

      Returns:
      the default charset of the system's default locale, as a Java charset. (NOT a MIME charset)
      Since:
      JavaMail 1.1
    • getDefaultMIMECharset

      static String getDefaultMIMECharset()
    • loadMappings

      private static void loadMappings(LineInputStream is, Map<String,String> table)
    • checkAscii

      static int checkAscii(String s)
      Check if the given string contains non US-ASCII characters.
      Parameters:
      s - string
      Returns:
      ALL_ASCII if all characters in the string belong to the US-ASCII charset. MOSTLY_ASCII if more than half of the available characters are US-ASCII characters. Else MOSTLY_NONASCII.
    • checkAscii

      static int checkAscii(byte[] b)
      Check if the given byte array contains non US-ASCII characters.
      Parameters:
      b - byte array
      Returns:
      ALL_ASCII if all characters in the string belong to the US-ASCII charset. MOSTLY_ASCII if more than half of the available characters are US-ASCII characters. Else MOSTLY_NONASCII. XXX - this method is no longer used
    • checkAscii

      static int checkAscii(InputStream is, int max, boolean breakOnNonAscii)
      Check if the given input stream contains non US-ASCII characters. Upto max bytes are checked. If max is set to ALL, then all the bytes available in this input stream are checked. If breakOnNonAscii is true the check terminates when the first non-US-ASCII character is found and MOSTLY_NONASCII is returned. Else, the check continues till max bytes or till the end of stream.
      Parameters:
      is - the input stream
      max - maximum bytes to check for. The special value ALL indicates that all the bytes in this input stream must be checked.
      breakOnNonAscii - if true, then terminate the the check when the first non-US-ASCII character is found.
      Returns:
      ALL_ASCII if all characters in the string belong to the US-ASCII charset. MOSTLY_ASCII if more than half of the available characters are US-ASCII characters. Else MOSTLY_NONASCII.
    • nonascii

      static final boolean nonascii(int b)
    • getBytes

      public static byte[] getBytes(String s)
    • getBytes

      public static byte[] getBytes(InputStream is) throws IOException
      Throws:
      IOException
    • getBooleanProperty

      static boolean getBooleanProperty(Properties props, String name, boolean def)
      Get a boolean valued property.
      Parameters:
      props - the properties
      name - the property name
      def - default value if property not found
      Returns:
      the property value
    • getBooleanSystemProperty

      static boolean getBooleanSystemProperty(String name, boolean def)
      Get a boolean valued System property.
      Parameters:
      name - the property name
      def - default value if property not found
      Returns:
      the property value
    • getProp

      private static Object getProp(Properties props, String name)
      Get the value of the specified property. If the "get" method returns null, use the getProperty method, which might cascade to a default Properties object.
    • getBoolean

      private static boolean getBoolean(Object value, boolean def)
      Interpret the value object as a boolean, returning def if unable.