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javax.mail.internet

Class MimeUtility

java.lang.Object
|
+--javax.mail.internet.MimeUtility


public class MimeUtility
extends java.lang.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. 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
Author:

Method Summary

static InputStream

decode(InputStream is, String encoding)

Decode the given input stream.

static String

decodeText(String etext)

Decode "unstructured" headers, that is, headers that are defined as '*text' as per RFC 822.

static String

decodeWord(String text)

The string is parsed using the rules in RFC 2047 for parsing an "encoded-word".

static OutputStream

encode(OutputStream os, String encoding)

Wrap an encoder around the given output stream.

static OutputStream

encode(OutputStream os, String encoding, String filename)

Wrap an encoder around the given output stream.

static String

encodeText(String text)

Encode a RFC 822 "text" token into mail-safe form as per RFC 2047.

static String

encodeText(String text, String charset, String encoding)

Encode a RFC 822 "text" token into mail-safe form as per RFC 2047.

static String

encodeWord(String text)

Encode a RFC 822 "word" token into mail-safe form as per RFC 2047.

static String

encodeWord(String text, String charset, String encoding)

Encode a RFC 822 "word" token into mail-safe form as per RFC 2047.

static String

getDefaultJavaCharset()

Get the default charset corresponding to the system's current default locale.

static String

getEncoding(DataSource ds)

Get the content-transfer-encoding that should be applied to the input stream of this datasource, to make it mailsafe.

static String

getEncoding(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.

static String

javaCharset(String charset)

Convert a MIME charset name into a valid Java charset name.

static String

mimeCharset(String charset)

Convert a java charset into its MIME charset name.

static String

quote(String text, String specials)

A utility method to quote a word, if the word contains any characters from the specified 'specials' list.

Method Details

decode

public static InputStream decode(InputStream is, String encoding)

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 "base64", "quoted-printable", "7bit", "8bit", and "binary". In addition, "uuencode" is also supported.

Parameters:
is - input stream
encoding - the encoding of the stream.
Returns:
decoded input stream.

decodeText

public static String decodeText(String etext)

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 6.1.1. 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
Throws:
- if the charset conversion failed.

decodeWord

public static String decodeWord(String text)

The string is parsed using the rules in RFC 2047 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:
text - the possibly encoded value
Throws:
ParseException - if the string is not an encoded-word as per RFC 2047.
- if the charset conversion failed.

encode

public static OutputStream encode(OutputStream os, String encoding)

Wrap an encoder around the given output stream. All the encodings defined in RFC 2045 are supported here. They include "base64", "quoted-printable", "7bit", "8bit" and "binary". In addition, "uuencode" is also supported.

Parameters:
os - output stream
encoding - the encoding of the stream.
Returns:
output stream that applies the specified encoding.

encode

public static OutputStream encode(OutputStream os, String encoding, String filename)

Wrap an encoder around the given output stream. All the encodings defined in RFC 2045 are supported here. They include "base64", "quoted-printable", "7bit", "8bit" and "binary". In addition, "uuencode" is also supported. The filename parameter is used with the "uuencode" 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.

encodeText

public static String encodeText(String text)

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() failur

Parameters:
text - unicode string
Returns:
Unicode string containing only US-ASCII characters

encodeText

public static String encodeText(String text, String charset, String encoding)

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.

Parameters:
text - the header value
charset - the charset.
encoding - the encoding to be used.
Returns:
Unicode string containing only US-ASCII characters

encodeWord

public static String encodeWord(String text)

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:
text - unicode string
Returns:
Unicode string containing only US-ASCII characters.
Throws:
- if the encoding fails

encodeWord

public static String encodeWord(String text, String charset, String encoding)

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.

Parameters:
text - unicode string
charset - the MIME charset
encoding - the encoding to be used.
Returns:
Unicode string containing only US-ASCII characters
Throws:
- if the encoding fails

getDefaultJavaCharset

public static String getDefaultJavaCharset()

Get the default charset corresponding to the system's current default locale.

Returns:
the default charset of the system's default locale, as a Java charset. (NOT a MIME charset)

getEncoding

public static String getEncoding(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

getEncoding

public static String getEncoding(DataSource ds)

Get the content-transfer-encoding that should be applied to the input stream of this datasource, to make it mailsafe.

The algorithm used here is:

Parameters:
ds - DataSource
Returns:
the encoding. This is either "7bit", "quoted-printable" or "base64"

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.

quote

public static String quote(String text, 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:
text - word to be quoted
specials - the set of special characters
Returns:
the possibly quoted word