java.util

Class Properties

public class Properties extends Hashtable<Object,Object>

A set of persistent properties, which can be saved or loaded from a stream. A property list may also contain defaults, searched if the main list does not contain a property for a given key. An example of a properties file for the german language is given here. This extends the example given in ListResourceBundle. Create a file MyResource_de.properties with the following contents and put it in the CLASSPATH. (The character \u00e4 is the german umlaut)

s1=3
s2=MeineDisk
s3=3. M\u00e4rz 96
s4=Die Diskette ''{1}'' enth\u00e4lt {0} in {2}.
s5=0
s6=keine Dateien
s7=1
s8=eine Datei
s9=2
s10={0,number} Dateien
s11=Das Formatieren schlug fehl mit folgender Exception: {0}
s12=FEHLER
s13=Ergebnis
s14=Dialog
s15=Auswahlkriterium
s16=1,3

Although this is a sub class of a hash table, you should never insert anything other than strings to this property, or several methods, that need string keys and values, will fail. To ensure this, you should use the get/setProperty method instead of get/put. Properties are saved in ISO 8859-1 encoding, using Unicode escapes with a single u for any character which cannot be represented.

Field Summary
protected Properties	defaults The property list that contains default values for any keys not in this property list.

Constructor Summary
	Properties() Creates a new empty property list with no default values.
	Properties(Properties defaults) Create a new empty property list with the specified default values.

Method Summary
String	getProperty(String key) Gets the property with the specified key in this property list.
String	getProperty(String key, String defaultValue) Gets the property with the specified key in this property list.
void	list(PrintStream out) Prints the key/value pairs to the given print stream.
void	list(PrintWriter out) Prints the key/value pairs to the given print writer.
void	load(InputStream inStream) Reads a property list from an input stream.
void	loadFromXML(InputStream in) Decodes the contents of the supplied `InputStream` as an XML file, which represents a set of properties.
Enumeration<?>	propertyNames() Returns an enumeration of all keys in this property list, including the keys in the default property list.
Object	setProperty(String key, String value) Adds the given key/value pair to this properties.
void	store(OutputStream out, String header) Writes the key/value pairs to the given output stream, in a format suitable for `load`. If header is not null, this method writes a comment containing the header as first line to the stream.
void	storeToXML(OutputStream os, String comment) Encodes the properties as an XML file using the UTF-8 encoding.
void	storeToXML(OutputStream os, String comment, String encoding) Encodes the properties as an XML file using the supplied encoding.

Field Detail

defaults

protected Properties defaults

The property list that contains default values for any keys not in this property list.

Serial: the default properties

Constructor Detail

Properties

public Properties()

Creates a new empty property list with no default values.

Properties

public Properties(Properties defaults)

Create a new empty property list with the specified default values.

Parameters: defaults a Properties object containing the default values

Method Detail

getProperty

public String getProperty(String key)

Gets the property with the specified key in this property list. If the key is not found, the default property list is searched. If the property is not found in the default, null is returned.

Parameters: key The key for this property

Returns: the value for the given key, or null if not found

Throws: ClassCastException if this property contains any key or value that isn't a string

getProperty

public String getProperty(String key, String defaultValue)

Gets the property with the specified key in this property list. If the key is not found, the default property list is searched. If the property is not found in the default, the specified defaultValue is returned.

Parameters: key The key for this property defaultValue A default value

Returns: The value for the given key

Throws: ClassCastException if this property contains any key or value that isn't a string

list

public void list(PrintStream out)

Prints the key/value pairs to the given print stream. This is mainly useful for debugging purposes.

Parameters: out the print stream, where the key/value pairs are written to

Throws: ClassCastException if this property contains a key or a value that isn't a string

list

public void list(PrintWriter out)

Prints the key/value pairs to the given print writer. This is mainly useful for debugging purposes.

Parameters: out the print writer where the key/value pairs are written to

Throws: ClassCastException if this property contains a key or a value that isn't a string

Since: 1.1

load

public void load(InputStream inStream)

Reads a property list from an input stream. The stream should have the following format:
An empty line or a line starting with # or ! is ignored. An backslash (\) at the end of the line makes the line continueing on the next line (but make sure there is no whitespace after the backslash). Otherwise, each line describes a key/value pair.
The chars up to the first whitespace, = or : are the key. You can include this caracters in the key, if you precede them with a backslash (\). The key is followed by optional whitespaces, optionally one = or :, and optionally some more whitespaces. The rest of the line is the resource belonging to the key.
Escape sequences \t, \n, \r, \\, \", \', \!, \#, \ (a space), and unicode characters with the \\uxxxx notation are detected, and converted to the corresponding single character.

# This is a comment
key     = value
k\:5      \ a string starting with space and ending with newline\n
# This is a multiline specification; note that the value contains
# no white space.
weekdays: Sunday,Monday,Tuesday,Wednesday,\\
          Thursday,Friday,Saturday
# The safest way to include a space at the end of a value:
label   = Name:\\u0020

Parameters: inStream the input stream

Throws: IOException if an error occurred when reading the input NullPointerException if in is null

loadFromXML

public void loadFromXML(InputStream in)

Decodes the contents of the supplied InputStream as an XML file, which represents a set of properties. The format of the XML file must match the DTD http://java.sun.com/dtd/properties.dtd.

Parameters: in the input stream from which to receive the XML data.

Throws: IOException if an I/O error occurs in reading the input data. InvalidPropertiesFormatException if the input data does not constitute an XML properties file. NullPointerException if in is null.

Since: 1.5

propertyNames

public Enumeration<?> propertyNames()

Returns an enumeration of all keys in this property list, including the keys in the default property list.

Returns: an Enumeration of all defined keys

setProperty

public Object setProperty(String key, String value)

Adds the given key/value pair to this properties. This calls the hashtable method put.

Parameters: key the key for this property value the value for this property

Returns: The old value for the given key

Since: 1.2

store

public void store(OutputStream out, String header)

Writes the key/value pairs to the given output stream, in a format suitable for load.
If header is not null, this method writes a comment containing the header as first line to the stream. The next line (or first line if header is null) contains a comment with the current date. Afterwards the key/value pairs are written to the stream in the following format.
Each line has the form key = value. Newlines, Returns and tabs are written as \n,\t,\r resp. The characters \, !, #, = and : are preceeded by a backslash. Spaces are preceded with a backslash, if and only if they are at the beginning of the key. Characters that are not in the ascii range 33 to 127 are written in the \uxxxx Form.
Following the listing, the output stream is flushed but left open.

Parameters: out the output stream header the header written in the first line, may be null

Throws: ClassCastException if this property contains any key or value that isn't a string IOException if writing to the stream fails NullPointerException if out is null

Since: 1.2

storeToXML

public void storeToXML(OutputStream os, String comment)

Encodes the properties as an XML file using the UTF-8 encoding. The format of the XML file matches the DTD http://java.sun.com/dtd/properties.dtd.

Invoking this method provides the same behaviour as invoking storeToXML(os, comment, "UTF-8").

Parameters: os the stream to output to. comment a comment to include at the top of the XML file, or null if one is not required.

Throws: IOException if the serialization fails. NullPointerException if os is null.

Since: 1.5

storeToXML

public void storeToXML(OutputStream os, String comment, String encoding)

Encodes the properties as an XML file using the supplied encoding. The format of the XML file matches the DTD http://java.sun.com/dtd/properties.dtd.

Parameters: os the stream to output to. comment a comment to include at the top of the XML file, or null if one is not required. encoding the encoding to use for the XML output.

Throws: IOException if the serialization fails. NullPointerException if os or encoding is null.

Since: 1.5