public class Properties extends Hashtable
Properties class represents a persistent set of
properties. The Properties can be saved to a stream
or loaded from a stream. Each key and its corresponding value in
the property list is a string.
A property list can contain another property list as its "defaults"; this second property list is searched if the property key is not found in the original property list.
Because Properties inherits from Hashtable, the
put and putAll methods can be applied to a
Properties object. Their use is strongly discouraged as they
allow the caller to insert entries whose keys or values are not
Strings. The setProperty method should be used
instead. If the store or save method is called
on a "compromised" Properties object that contains a
non-String key or value, the call will fail.
When saving properties to a stream or loading them from a stream, the ISO 8859-1 character encoding is used. For characters that cannot be directly represented in this encoding, Unicode escapes are used; however, only a single 'u' character is allowed in an escape sequence. The native2ascii tool can be used to convert property files to and from other character encodings.
| Modifier and Type | Field and Description |
|---|---|
protected Properties |
defaults
A property list that contains default values for any keys not
found in this property list.
|
| Constructor and Description |
|---|
Properties()
Creates an empty property list with no default values.
|
Properties(Properties defaults)
Creates an empty property list with the specified defaults.
|
| Modifier and Type | Method and Description |
|---|---|
String |
getProperty(String key)
Searches for the property with the specified key in this property list.
|
String |
getProperty(String key,
String defaultValue)
Searches for the property with the specified key in this property list.
|
void |
list(PrintStream out)
Prints this property list out to the specified output stream.
|
void |
list(PrintWriter out)
Prints this property list out to the specified output stream.
|
void |
load(InputStream inStream)
Reads a property list (key and element pairs) from the input
stream.
|
Enumeration |
propertyNames()
Returns an enumeration of all the keys in this property list,
including distinct keys in the default property list if a key
of the same name has not already been found from the main
properties list.
|
void |
save(OutputStream out,
String header)
Deprecated.
This method does not throw an IOException if an I/O error
occurs while saving the property list. As of the Java 2 platform v1.2, the preferred
way to save a properties list is via the
store(OutputStream out,
String header) method. |
Object |
setProperty(String key,
String value)
Calls the Hashtable method
put. |
void |
store(OutputStream out,
String header)
Writes this property list (key and element pairs) in this
Properties table to the output stream in a format suitable
for loading into a Properties table using the
load method. |
protected Properties defaults
public Properties()
public Properties(Properties defaults)
defaults - the defaults.public Object setProperty(String key, String value)
put. Provided for
parallelism with the getProperty method. Enforces use of
strings for property keys and values. The value returned is the
result of the Hashtable call to put.key - the key to be placed into this property list.value - the value corresponding to key.null if it did not have one.getProperty(java.lang.String)public void load(InputStream inStream) throws IOException
\b does not
represent a backspace 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 'b'.
IllegalArgumentException is thrown if a
malformed Unicode escape appears in the input.
This method processes input in terms of lines. A natural line
of input is terminated either by a set of line terminator
characters (\n or \r or
\r\n) or by the end of the file. A natural line
may be either a blank line, a comment line, or hold some part
of a key-element pair. The logical line holding all the data
for a key-element pair 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. If a logical line is continued over several natural
lines, the continuation lines receive further processing, also
described below. Lines are read from the input stream until
end of file is reached.
A natural line that contains only white space characters is
considered blank and is ignored. A comment line has an ASCII
'#' or '!' 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 method considers the characters space
(' ', '\u0020'), tab
('\t', '\u0009'), and form feed
('\f', '\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 the following line have no affect on the key or element values. The remainder of the discussion of key and element parsing 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 to see 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 \r and
\n escape sequences. Any white space after the
key is skipped; if the first non-white space character after
the key is '=' or ':', 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
"Beauty":
Truth = Beauty
Truth:Beauty
Truth :Beauty
As another example, the following three lines specify a single
property:
fruits apple, banana, pear, \
cantaloupe, watermelon, \
kiwi, mango
The key is "fruits" 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:
cheesesspecifies that the key is
"cheeses" and the associated
element is the empty string "".inStream - the input stream.IOException - if an error occurred when reading from the
input stream.IllegalArgumentException - if the input stream contains a
malformed Unicode escape sequence.public void save(OutputStream out, String header)
store(OutputStream out,
String header) method.store(OutputStream out, String header) method
and suppresses IOExceptions that were thrown.out - an output stream.header - a description of the property list.ClassCastException - if this Properties object
contains any keys or values that are not Strings.public void store(OutputStream out, String header) throws IOException
Properties table to the output stream in a format suitable
for loading into a Properties table using the
load method.
The stream is written using the ISO 8859-1 character encoding.
Properties from the defaults table of this Properties
table (if any) are not written out by this method.
If the header argument is not null, then an ASCII #
character, the header string, and a line separator are first written
to the output stream. Thus, the header can serve as an
identifying comment.
Next, a comment line is always written, consisting of an ASCII
# character, the current date and time (as if produced
by the toString method of Date for the
current time), and a line separator as generated by the Writer.
Then every entry in this Properties table is
written out, one per line. For each entry the key string is
written, then an ASCII =, then the associated
element string. Each character of the key and element strings
is examined to see whether it should be rendered as an escape
sequence. The ASCII characters \, tab, form feed,
newline, and carriage return are written as \\,
\t, \f \n, and
\r, respectively. Characters less than
\u0020 and characters greater than
\u007E are written as
\uxxxx for the appropriate hexadecimal
value xxxx. For the key, all space characters are
written with a preceding \ character. For the
element, leading space characters, but not embedded or trailing
space characters, are written with a preceding \
character. The key and element characters #,
!, =, and : are written
with a preceding backslash to ensure that they are properly loaded.
After the entries have been written, the output stream is flushed. The output stream remains open after this method returns.
out - an output stream.header - a description of the property list.IOException - if writing this property list to the specified
output stream throws an IOException.ClassCastException - if this Properties object
contains any keys or values that are not Strings.NullPointerException - if out is null.public String getProperty(String key)
null if the property is not found.key - the property key.setProperty(java.lang.String, java.lang.String),
defaultspublic String getProperty(String key, String defaultValue)
key - the hashtable key.defaultValue - a default value.setProperty(java.lang.String, java.lang.String),
defaultspublic Enumeration propertyNames()
Enumeration,
defaultspublic void list(PrintStream out)
out - an output stream.public void list(PrintWriter out)
out - an output stream.Copyright © 2012 CableLabs. All Rights Reserved.