MessageFormat
provides a means to produce concatenated
messages in language-neutral way. Use this to construct messages
displayed for end users.
MessageFormat
takes a set of objects, formats them, then
inserts the formatted strings into the pattern at the appropriate places.
Note:
MessageFormat
differs from the other
Format
classes in that you create a
MessageFormat
object with one
of its constructors (not with a
getInstance
style factory
method). The factory methods aren't necessary because
MessageFormat
itself doesn't implement locale specific behavior. Any locale specific
behavior is defined by the pattern that you provide as well as the
subformats used for inserted arguments.
MessageFormat
uses patterns of the following form:
MessageFormatPattern:
String
MessageFormatPattern FormatElement String
FormatElement:
{ ArgumentIndex }
{ ArgumentIndex , FormatType }
{ ArgumentIndex , FormatType , FormatStyle }
FormatType: one of
number date time choice
FormatStyle:
short
medium
long
full
integer
currency
percent
SubformatPattern
String:
StringPartopt
String StringPart
StringPart:
''
' QuotedString '
UnquotedString
SubformatPattern:
SubformatPatternPartopt
SubformatPattern SubformatPatternPart
SubFormatPatternPart:
' QuotedPattern '
UnquotedPattern
Within a
String,
"''"
represents a single
quote. A
QuotedString can contain arbitrary characters
except single quotes; the surrounding single quotes are removed.
An
UnquotedString can contain arbitrary characters
except single quotes and left curly brackets. Thus, a string that
should result in the formatted message "'{0}'" can be written as
"'''{'0}''"
or
"'''{0}'''"
.
Within a
SubformatPattern, different rules apply.
A
QuotedPattern can contain arbitrary characters
except single quotes; but the surrounding single quotes are
not removed, so they may be interpreted by the
subformat. For example,
"{1,number,$'#',##}"
will
produce a number format with the pound-sign quoted, with a result
such as: "$#31,45".
An
UnquotedPattern can contain arbitrary characters
except single quotes, but curly braces within it must be balanced.
For example,
"ab {0} de"
and
"ab '}' de"
are valid subformat patterns, but
"ab {0'}' de"
and
"ab } de"
are not.
- Warning:
The
ArgumentIndex value is a non-negative integer written
using the digits '0' through '9', and represents an index into the
arguments
array passed to the
format
methods
or the result array returned by the
parse
methods.
The
FormatType and
FormatStyle values are used to create
a
Format
instance for the format element. The following
table shows how the values map to Format instances. Combinations not
shown in the table are illegal. A
SubformatPattern must
be a valid pattern string for the Format subclass used.
Format Type
| Format Style
| Subformat Created
|
---|
(none)
| null
|
number
| (none)
| NumberFormat.getInstance(getLocale())
|
integer
| NumberFormat.getIntegerInstance(getLocale())
|
currency
| NumberFormat.getCurrencyInstance(getLocale())
|
percent
| NumberFormat.getPercentInstance(getLocale())
|
SubformatPattern
| new DecimalFormat(subformatPattern, new DecimalFormatSymbols(getLocale()))
|
date
| (none)
| DateFormat.getDateInstance(DateFormat.DEFAULT, getLocale())
|
short
| DateFormat.getDateInstance(DateFormat.SHORT, getLocale())
|
medium
| DateFormat.getDateInstance(DateFormat.DEFAULT, getLocale())
|
long
| DateFormat.getDateInstance(DateFormat.LONG, getLocale())
|
full
| DateFormat.getDateInstance(DateFormat.FULL, getLocale())
|
SubformatPattern
| new SimpleDateFormat(subformatPattern, getLocale())
|
time
| (none)
| DateFormat.getTimeInstance(DateFormat.DEFAULT, getLocale())
|
short
| DateFormat.getTimeInstance(DateFormat.SHORT, getLocale())
|
medium
| DateFormat.getTimeInstance(DateFormat.DEFAULT, getLocale())
|
long
| DateFormat.getTimeInstance(DateFormat.LONG, getLocale())
|
full
| DateFormat.getTimeInstance(DateFormat.FULL, getLocale())
|
SubformatPattern
| new SimpleDateFormat(subformatPattern, getLocale())
|
choice
| SubformatPattern
| new ChoiceFormat(subformatPattern)
|
Usage Information
Here are some examples of usage:
Object[] arguments = {
new Integer(7),
new Date(System.currentTimeMillis()),
"a disturbance in the Force"
};
String result = MessageFormat.format(
"At {1,time} on {1,date}, there was {2} on planet {0,number,integer}.",
arguments);
output: At 12:30 PM on Jul 3, 2053, there was a disturbance
in the Force on planet 7.
Typically, the message format will come from resources, and the
arguments will be dynamically set at runtime.
Example 2:
Object[] testArgs = {new Long(3), "MyDisk"};
MessageFormat form = new MessageFormat(
"The disk \"{1}\" contains {0} file(s).");
System.out.println(form.format(testArgs));
// output, with different testArgs
output: The disk "MyDisk" contains 0 file(s).
output: The disk "MyDisk" contains 1 file(s).
output: The disk "MyDisk" contains 1,273 file(s).
For more sophisticated patterns, you can use a
ChoiceFormat
to get
output such as:
MessageFormat form = new MessageFormat("The disk \"{1}\" contains {0}.");
double[] filelimits = {0,1,2};
String[] filepart = {"no files","one file","{0,number} files"};
ChoiceFormat fileform = new ChoiceFormat(filelimits, filepart);
form.setFormatByArgumentIndex(0, fileform);
Object[] testArgs = {new Long(12373), "MyDisk"};
System.out.println(form.format(testArgs));
// output, with different testArgs
output: The disk "MyDisk" contains no files.
output: The disk "MyDisk" contains one file.
output: The disk "MyDisk" contains 1,273 files.
You can either do this programmatically, as in the above example,
or by using a pattern (see
ChoiceFormat
for more information) as in:
form.applyPattern(
"There {0,choice,0#are no files|1#is one file|1<are {0,number,integer} files}.");
Note: As we see above, the string produced
by a
ChoiceFormat
in
MessageFormat
is treated specially;
occurances of '{' are used to indicated subformats, and cause recursion.
If you create both a
MessageFormat
and
ChoiceFormat
programmatically (instead of using the string patterns), then be careful not to
produce a format that recurses on itself, which will cause an infinite loop.
When a single argument is parsed more than once in the string, the last match
will be the final result of the parsing. For example,
MessageFormat mf = new MessageFormat("{0,number,#.##}, {0,number,#.#}");
Object[] objs = {new Double(3.1415)};
String result = mf.format( objs );
// result now equals "3.14, 3.1"
objs = null;
objs = mf.parse(result, new ParsePosition(0));
// objs now equals {new Double(3.1)}
Likewise, parsing with a MessageFormat object using patterns containing
multiple occurances of the same argument would return the last match. For
example,
MessageFormat mf = new MessageFormat("{0}, {0}, {0}");
String forParsing = "x, y, z";
Object[] objs = mf.parse(forParsing, new ParsePosition(0));
// result now equals {new String("z")}
Message formats are not synchronized.
It is recommended to create separate format instances for each thread.
If multiple threads access a format concurrently, it must be synchronized
externally.
applyPattern
public void applyPattern(String pattern)
Sets the pattern used by this message format.
The method parses the pattern and creates a list of subformats
for the format elements contained in it.
Patterns and their interpretation are specified in the
class description.
pattern
- the pattern for this message format
autoQuoteApostrophe
public static String autoQuoteApostrophe(String pattern)
Convert an 'apostrophe-friendly' pattern into a standard
pattern. Standard patterns treat all apostrophes as
quotes, which is problematic in some languages, e.g.
French, where apostrophe is commonly used. This utility
assumes that only an unpaired apostrophe immediately before
a brace is a true quote. Other unpaired apostrophes are paired,
and the resulting standard pattern string is returned.
Note it is not guaranteed that the returned pattern
is indeed a valid pattern. The only effect is to convert
between patterns having different quoting semantics.
pattern
- the 'apostrophe-friendly' patttern to convert
- the standard equivalent of the original pattern
clone
public Object clone()
Creates and returns a copy of this object.
- a clone of this instance.
equals
public boolean equals(Object obj)
Equality comparison between two message format objects
format
public final StringBuffer format(Object arguments,
StringBuffer result,
FieldPosition pos)
Formats an array of objects and appends the
MessageFormat
's
pattern, with format elements replaced by the formatted objects, to the
provided
StringBuffer
.
This is equivalent to
format
((Object[]) arguments, result, pos)
arguments
- an array of objects to be formatted and substituted.result
- where text is appended.pos
- On input: an alignment field, if desired.
On output: the offsets of the alignment field.
format
public final StringBuffer format(Object[] arguments,
StringBuffer result,
FieldPosition pos)
Formats an array of objects and appends the
MessageFormat
's
pattern, with format elements replaced by the formatted objects, to the
provided
StringBuffer
.
The text substituted for the individual format elements is derived from
the current subformat of the format element and the
arguments
element at the format element's argument index
as indicated by the first matching line of the following table. An
argument is
unavailable if
arguments
is
null
or has fewer than argumentIndex+1 elements.
Subformat
| Argument
| Formatted Text
|
---|
any
| unavailable
| "{" + argumentIndex + "}"
|
any
| null
| "null"
|
instanceof ChoiceFormat
| any
| subformat.format(argument).indexOf('{') >= 0 ?
(new MessageFormat(subformat.format(argument), getLocale())).format(argument) :
subformat.format(argument)
|
!= null
| any
| subformat.format(argument)
|
null
| instanceof Number
| NumberFormat.getInstance(getLocale()).format(argument)
|
null
| instanceof Date
| DateFormat.getDateTimeInstance(DateFormat.SHORT, DateFormat.SHORT, getLocale()).format(argument)
|
null
| instanceof String
| argument
|
null
| any
| argument.toString()
|
If
pos
is non-null, and refers to
Field.ARGUMENT
, the location of the first formatted
string will be returned.
arguments
- an array of objects to be formatted and substituted.result
- where text is appended.pos
- On input: an alignment field, if desired.
On output: the offsets of the alignment field.
format
public static String format(String pattern,
Object[] arguments)
Creates a MessageFormat with the given pattern and uses it
to format the given arguments. This is equivalent to
(new MessageFormat
(pattern)).format
(arguments, new StringBuffer(), null).toString()
getFormats
public Format[] getFormats()
Gets the formats used for the format elements in the
previously set pattern string.
The order of formats in the returned array corresponds to
the order of format elements in the pattern string.
Since the order of format elements in a pattern string often
changes during localization, it's generally better to use the
getFormatsByArgumentIndex
method, which assumes an order of formats corresponding to the
order of elements in the
arguments
array passed to
the
format
methods or the result array returned by
the
parse
methods.
- the formats used for the format elements in the pattern
getFormatsByArgumentIndex
public Format[] getFormatsByArgumentIndex()
Gets the formats used for the values passed into
format
methods or returned from
parse
methods. The indices of elements in the returned array
correspond to the argument indices used in the previously set
pattern string.
The order of formats in the returned array thus corresponds to
the order of elements in the
arguments
array passed
to the
format
methods or the result array returned
by the
parse
methods.
If an argument index is used for more than one format element
in the pattern string, then the format used for the last such
format element is returned in the array. If an argument index
is not used for any format element in the pattern string, then
null is returned in the array.
- the formats used for the arguments within the pattern
getLocale
public Locale getLocale()
Gets the locale that's used when creating or comparing subformats.
- the locale used when creating or comparing subformats
getULocale
public ULocale getULocale()
Gets the locale that's used when creating or comparing subformats.
- the locale used when creating or comparing subformats
hashCode
public int hashCode()
Generates a hash code for the message format object.
parse
public Object[] parse(String source)
throws ParseException
Parses text from the beginning of the given string to produce an object
array.
The method may not use the entire text of the given string.
See the
parse(String,ParsePosition)
method for more information
on message parsing.
source
- A String
whose beginning should be parsed.
- An
Object
array parsed from the string.
parse
public Object[] parse(String source,
ParsePosition pos)
Parses the string.
Caveats: The parse may fail in a number of circumstances.
For example:
- If one of the arguments does not occur in the pattern.
- If the format of an argument loses information, such as
with a choice format where a large number formats to "many".
- Does not yet handle recursion (where
the substituted strings contain {n} references.)
- Will not always find a match (or the correct match)
if some part of the parse is ambiguous.
For example, if the pattern "{1},{2}" is used with the
string arguments {"a,b", "c"}, it will format as "a,b,c".
When the result is parsed, it will return {"a", "b,c"}.
- If a single argument is parsed more than once in the string,
then the later parse wins.
When the parse fails, use ParsePosition.getErrorIndex() to find out
where in the string did the parsing failed. The returned error
index is the starting offset of the sub-patterns that the string
is comparing with. For example, if the parsing string "AAA {0} BBB"
is comparing against the pattern "AAD {0} BBB", the error index is
0. When an error occurs, the call to this method will return null.
If the source is null, return an empty array.
parseObject
public Object parseObject(String source,
ParsePosition pos)
Parses text from a string to produce an object array.
The method attempts to parse text starting at the index given by
pos
.
If parsing succeeds, then the index of
pos
is updated
to the index after the last character used (parsing does not necessarily
use all characters up to the end of the string), and the parsed
object array is returned. The updated
pos
can be used to
indicate the starting point for the next call to this method.
If an error occurs, then the index of
pos
is not
changed, the error index of
pos
is set to the index of
the character where the error occurred, and null is returned.
See the
parse(String,ParsePosition)
method for more information
on message parsing.
source
- A String
, part of which should be parsed.pos
- A ParsePosition
object with index and error
index information as described above.
- An
Object
array parsed from the string. In case of
error, returns null.
setFormat
public void setFormat(int formatElementIndex,
Format newFormat)
Sets the format to use for the format element with the given
format element index within the previously set pattern string.
The format element index is the zero-based number of the format
element counting from the start of the pattern string.
Since the order of format elements in a pattern string often
changes during localization, it is generally better to use the
setFormatByArgumentIndex
method, which accesses format elements based on the argument
index they specify.
formatElementIndex
- the index of a format element within the patternnewFormat
- the format to use for the specified format element
setFormatByArgumentIndex
public void setFormatByArgumentIndex(int argumentIndex,
Format newFormat)
Sets the format to use for the format elements within the
previously set pattern string that use the given argument
index.
The argument index is part of the format element definition and
represents an index into the
arguments
array passed
to the
format
methods or the result array returned
by the
parse
methods.
If the argument index is used for more than one format element
in the pattern string, then the new format is used for all such
format elements. If the argument index is not used for any format
element in the pattern string, then the new format is ignored.
argumentIndex
- the argument index for which to use the new formatnewFormat
- the new format to use
setFormats
public void setFormats(Format[] newFormats)
Sets the formats to use for the format elements in the
previously set pattern string.
The order of formats in
newFormats
corresponds to
the order of format elements in the pattern string.
If more formats are provided than needed by the pattern string,
the remaining ones are ignored. If fewer formats are provided
than needed, then only the first
newFormats.length
formats are replaced.
Since the order of format elements in a pattern string often
changes during localization, it is generally better to use the
setFormatsByArgumentIndex
method, which assumes an order of formats corresponding to the
order of elements in the
arguments
array passed to
the
format
methods or the result array returned by
the
parse
methods.
newFormats
- the new formats to use
setFormatsByArgumentIndex
public void setFormatsByArgumentIndex(Format[] newFormats)
Sets the formats to use for the values passed into
format
methods or returned from
parse
methods. The indices of elements in
newFormats
correspond to the argument indices used in the previously set
pattern string.
The order of formats in
newFormats
thus corresponds to
the order of elements in the
arguments
array passed
to the
format
methods or the result array returned
by the
parse
methods.
If an argument index is used for more than one format element
in the pattern string, then the corresponding new format is used
for all such format elements. If an argument index is not used
for any format element in the pattern string, then the
corresponding new format is ignored. If fewer formats are provided
than needed, then only the formats for argument indices less
than
newFormats.length
are replaced.
newFormats
- the new formats to use
setLocale
public void setLocale(Locale locale)
Sets the locale to be used when creating or comparing subformats.
This affects subsequent calls to the
applyPattern
and
toPattern
methods as well as to the
format
and
formatToCharacterIterator
methods.
locale
- the locale to be used when creating or comparing subformats
setLocale
public void setLocale(ULocale locale)
Sets the locale to be used when creating or comparing subformats.
This affects subsequent calls to the
applyPattern
and
toPattern
methods as well as to the
format
and
formatToCharacterIterator
methods.
locale
- the locale to be used when creating or comparing subformats
toPattern
public String toPattern()
Returns a pattern representing the current state of the message format.
The string is constructed from internal information and therefore
does not necessarily equal the previously applied pattern.
- a pattern representing the current state of the message format