public class Properties extends Hashtable<Object,Object>
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. Similarly, the call to the propertyNames or list method will fail if it
is called on a "compromised" Properties object that contains a non-String key.
The load(Reader) / store(Writer, String) methods load and store properties from and to a character based stream in a simple
line-oriented format specified below.
The load(InputStream) /
store(OutputStream, String) methods work the same way as the
load(Reader)/store(Writer, String) pair, except the input/output stream is encoded in ISO 8859-1 character encoding.
Characters that cannot be directly represented in this encoding can be written using Unicode escapes as defined in
section 3.3 of The Java™ Language Specification; 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.
Properties object without the need for external synchronization.
| 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 byte stream.
|
void |
load(Reader reader)
Reads a property list (key and element pairs) from the input character stream in a simple line-oriented format.
|
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.
|
Object |
setProperty(String key,
String value)
Calls the Hashtable method
put. |
void |
store(OutputStream out,
String comments)
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(InputStream) method. |
void |
store(Writer writer,
String comments)
Writes this property list (key and element pairs) in this
Properties table to the output character stream
in a format suitable for using the load(Reader) method. |
Set<String> |
stringPropertyNames()
Returns a set of keys in this property list where the key and its corresponding value are strings, 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.
|
@Nullable protected Properties defaults
public Properties()
public Properties(Properties defaults)
defaults - the defaults.@Nullable public String getProperty(String key)
null
if the property is not found.key - the property key.setProperty(java.lang.String, java.lang.String),
defaults@Nullable public String getProperty(String key, @Nullable String defaultValue)
key - the hashtable key.defaultValue - a default value.setProperty(java.lang.String, java.lang.String),
defaultspublic void list(PrintStream out)
out - an output stream.ClassCastException - if any key in this property list is not a string.public void list(PrintWriter out)
out - an output stream.ClassCastException - if any key in this property list is not a string.public void load(InputStream inStream) throws IOException
load(Reader) and is assumed to use the ISO
8859-1 character encoding; that is each byte is one Latin1 character. Characters not in Latin1, and certain
special characters, are represented in keys and elements using Unicode escapes as defined in section 3.3 of
The Java™ Language Specification.
The specified stream remains open after this method returns.
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 load(Reader reader) throws IOException
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 (\n or \r or \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 '#' 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 format 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 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 \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 :BeautyAs 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 "".
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:
\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'.
The specified stream remains open after this method returns.
reader - the input character stream.IOException - if an error occurred when reading from the input stream.IllegalArgumentException - if a malformed Unicode escape appears in the input.public Enumeration<?> propertyNames()
ClassCastException - if any key in this property list is not a string.Enumeration,
defaults,
stringPropertyNames()@Nullable 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 store(OutputStream out, @Nullable String comments) throws IOException
Properties table to the output stream in a
format suitable for loading into a Properties table using the load(InputStream) method.
Properties from the defaults table of this Properties table (if any) are not written out by this
method.
This method outputs the comments, properties keys and values in the same format as specified in
store(Writer), with the following differences:
\uxxxx for their appropriate
unicode hexadecimal value xxxx.
\u0020 and characters greater than \u007E in property keys or
values are written as \uxxxx for the appropriate hexadecimal value xxxx.
After the entries have been written, the output stream is flushed. The output stream remains open after this method returns.
out - an output stream.comments - 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 void store(Writer writer, @Nullable String comments) throws IOException
Properties table to the output character stream
in a format suitable for using the load(Reader) method.
Properties from the defaults table of this Properties table (if any) are not written out by this
method.
If the comments argument is not null, then an ASCII # character, the comments string, and a line
separator are first written to the output stream. Thus, the comments can serve as an identifying comment.
Any one of a line feed ('\n'), a carriage return ('\r'), or a carriage return followed immediately by a line feed
in comments is replaced by a line separator generated by the Writer and if the next character in comments
is not character # or character ! then an ASCII # is written out after that line
separator.
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. 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.
writer - an output character stream writer.comments - 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 writer is null.public Set<String> stringPropertyNames()
The returned set is not backed by the Properties object. Changes to this Properties are not reflected in the set, or vice versa.
defaults