Reads a property list (key and element pairs) from the input character stream in a simple line-oriented format.
Properties are processed in terms of lines. There are two kinds of line, natural lines and logical lines . A natural line is defined as a line of characters that is terminated either by a set of line terminator characters (
\r\n) or by the end of the stream. A natural line may be either a blank line, a comment line, or hold all or some of a key-element pair. A logical line holds all the data of a key-element pair, which may be spread out across several adjacent natural lines by escaping the line terminator sequence with a backslash character
\. Note that a comment line cannot be extended in this manner; every natural line that is a comment must have its own comment indicator, as described below. Lines are read from input until the end of the stream is reached.
A natural line that contains only white space characters is considered blank and is ignored. A comment line has an ASCII
'!' as its first non-white space character; comment lines are also ignored and do not encode key-element information. In addition to line terminators, this format considers the characters space (
' ' ,
'\u0020'), tab (
'\u0009'), and form feed (
'\u000C') to be white space.
If a logical line is spread across several natural lines, the backslash escaping the line terminator sequence, the line terminator sequence, and any white space at the start of the following line have no affect on the key or element values. The remainder of the discussion of key and element parsing (when loading) will assume all the characters constituting the key and element appear on a single natural line after line continuation characters have been removed. Note that it is not sufficient to only examine the character preceding a line terminator sequence to decide if the line terminator is escaped; there must be an odd number of contiguous backslashes for the line terminator to be escaped. Since the input is processed from left to right, a non-zero even number of 2n contiguous backslashes before a line terminator (or elsewhere) encodes n backslashes after escape processing.
The key contains all of the characters in the line starting with the first non-white space character and up to, but not including, the first unescaped
':', or white space character other than a line terminator. All of these key termination characters may be included in the key by escaping them with a preceding backslash character; for example,
would be the two-character key
":=". Line terminator characters can be included using
\n escape sequences. Any white space after the key is skipped; if the first non-white space character after the key is
':', then it is ignored and any white space characters after it are also skipped. All remaining characters on the line become part of the associated element string; if there are no remaining characters, the element is the empty string
"". Once the raw character sequences constituting the key and element are identified, escape processing is performed as described above.
As an example, each of the following three lines specifies the key
"Truth" and the associated element value
Truth = Beauty
As another example, the following three lines specify a single property:
fruits apple, banana, pear, \
cantaloupe, watermelon, \
The key is
and the associated element is:
"apple, banana, pear, cantaloupe, watermelon, kiwi, mango"
Note that a space appears before each
so that a space will appear after each comma in the final result; the
, line terminator, and leading white space on the continuation line are merely discarded and are not
replaced by one or more other characters.
As a third example, the line:
specifies that the key is
and the associated element is the empty string
Characters in keys and elements can be represented in escape sequences similar to those used for character and string literals (see sections 3.3 and 3.10.6 of The Java™ Language Specification ). The differences from the character escape sequences and Unicode escapes used for characters and strings are:
- Octal escapes are not recognized.
- The character sequence
\b does not represent a backspace character.
- The method does not treat a backslash character,
\, before a non-valid escape character as an error; the backslash is silently dropped. For example, in a Java string the sequence
"\z" would cause a compile time error. In contrast, this method silently drops the backslash. Therefore, this method treats the two character sequence
"\b" as equivalent to the single character
- Escapes are not necessary for single and double quotes; however, by the rule above, single and double quote characters preceded by a backslash still yield single and double quote characters, respectively.
- Only a single 'u' character is allowed in a Unicode escape sequence.
The specified stream remains open after this method returns.