Practical Considerations when Writing Applets

Getting System Properties

To find out about the current working environment, applets can read system properties. System properties are key/value pairs that contain information such as the operating system that the applet is running under. System properties are covered in detail in the System Properties page.

Applets can read some, but not all, system properties. This page lists the system properties that Netscape Navigator 2.0 and the Applet Viewer allow applets to read, followed by a list of properties that applets can't read.

System Properties that Applets Can Read

Applets can read the following system properties:

Key	Meaning
"file.separator"	File separator (for example, "/")
"java.class.version"	Java class version number
"java.vendor"	Java vendor-specific string
"java.vendor.url"	Java vendor URL
"java.version"	Java version number
"line.separator"	Line separator
"os.arch"	Operating system architecture
"os.name"	Operating system name
"path.separator"	Path separator (for example, ":")

To read a system property from within an applet, the applet uses the System class method getProperty. For example:

String newline = System.getProperty("line.separator");

The following applet reads all of the properties that are available to all applets:

You can find the source code (which is the same in both 1.0 and 1.1) in GetOpenProperties.java.

Forbidden System Properties

For security reasons, no existing browsers or applet viewers let applets read the following system properties.

Key	Meaning
"java.class.path"	Java classpath
"java.home"	Java installation directory
"user.dir"	User's current working directory
"user.home"	User home directory
"user.name"	User account name

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Practical Considerations when Writing Applets