public class Properties extends Hashtable<String,String>
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
the keys in the default property 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.key - the key to be placed into this property list.value - the value corresponding to key.getProperty(java.lang.String)public void load(InputStream inStream) throws IOException
Every property occupies one line of the input stream. Each line
is terminated by a line terminator (\n or \r
or \r\n). Lines from the input stream are processed until
end of file is reached on the input stream.
A line that contains only whitespace or whose first non-whitespace
character is an ASCII # or ! is ignored
(thus, # or ! indicate comment lines).
Every line other than a blank line or a comment line describes one
property to be added to the table (except that if a line ends with \,
then the following line, if it exists, is treated as a continuation
line, as described
below). The key consists of all the characters in the line starting
with the first non-whitespace character and up to, but not including,
the first ASCII =, :, or whitespace
character. All of the key termination characters may be included in
the key by preceding them with a \.
Any whitespace after the key is skipped; if the first non-whitespace
character after the key is = or :, then it
is ignored and any whitespace characters after it are also skipped.
All remaining characters on the line become part of the associated
element string. Within the element string, the ASCII
escape sequences \t, \n,
\r, \\, \", \',
\ (a backslash and a space), and
\uxxxx are recognized and converted to single
characters. Moreover, if the last character on the line is
\, then the next line is treated as a continuation of the
current line; the \ and line terminator are simply
discarded, and any leading whitespace characters on the continuation
line are also discarded and are not part of the element string.
As an example, each of the following four 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 whitespace 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.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 element string is examined to see whether it should be rendered as
an escape sequence. The ASCII characters \, tab, newline,
and carriage return are written as \\, \t,
\n, and \r, respectively. Characters less
than \u0020 and characters greater than
\u007E are written as \uxxxx for
the appropriate hexadecimal value xxxx. Leading space characters,
but not embedded or trailing space characters, are written with a
preceding \. The key and value characters #,
!, =, and : are written with a
preceding slash 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.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.