.properties

.properties is a file extension for files mainly used in Java related technologies to store the configurable parameters of an application. They can also be used for storing strings for localization; these are known as Property Resource Bundles.

Each parameter is stored as a pair of strings, one storing the name of the parameter (called the key), and the other storing the value.

[edit] Format

Each line in a .properties file normally stores a single property. Several formats are possible for each line, including key=value, key = value, key:value, and key value.

.properties files can use the number sign (#) or the exclamation mark (!) as the first non blank character in a line to denote that all text following it is a comment. The backwards slash is used to escape a character. An example of a properties file is provided below.

# You are reading the ".properties" entry.
! The exclamation mark can also mark text as comments.
website = http://en.wikipedia.org
language = English
# The backslash below tells the application to continue reading
# the value onto the next line.
message = Welcome to \
          Wikipedia!
# Add spaces to the key
key\ with\ spaces = This is the value that could be looked up with the key "key with spaces".

In the example above, website would be a key, and its corresponding value would be http://en.wikipedia.org. While the number sign and the exclamation mark marks text as comments, it has no effect when it is part of a property. Thus, the key message has the value Welcome to Wikipedia! and not Welcome to Wikipedia. Note also that all of the whitespace in front of Wikipedia! is excluded completely.

The encoding of a .properties file is ISO-8859-1, also known as Latin-1. All non-Latin-1 characters must be entered by using Unicode escape characters, e. g. \uHHHH where HHHH is a hexadecimal index of the character in the Unicode character set. This allows for using .properties files as resource bundles for localization. A non-Latin-1 text file can be converted to a correct .properties file by using the native2ascii tool that is shipped with the JDK or by using a tool, such as prop2po^[1], that manages the transformation from a bilingual localization format into .properties escaping.

[edit] See also

• java.util.Properties.load(java.io.Reader) - gives the precise semantics of well-formed Java property files
• java.util.PropertyResourceBundle - describes property resource bundles

[edit] References

1. ^ Translate Toolkit's po2prop converts native character encodings in a Gettext PO file into correctly escaped ascii without the need for native2ascii

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