The key of system. getproperty (string key) in Java is found here.

One of the examples in "Java and mode" uses system. getproperty (string key)

System.getProperty("user.dir");

It's strange how he knows that the key is "user. dir ". Baidu has been sticking these keys for a long time. But where to find it? It took only half a day to find it:

In javase API, The getproperties method in the system class has the following descriptions:

Getproperties

public static Properties getProperties()

Determine the current system attribute.

First, if there is a security manager, directly call it without ParameterscheckPropertiesAccessMethod. This may cause a security exception.

SetgetProperty(String)The current system property set used by the methodPropertiesObject. If the current system property set does not exist, a system property set is created and initialized first. This system property set always contains the following key values:

Key	Description of related values
java.version	Java Runtime Environment version
java.vendor	Java Runtime Environment vendor
java.vendor.url	Java vendor URL
java.home	Java installation directory
java.vm.specification.version	Java Virtual Machine standard version
java.vm.specification.vendor	Java virtual machine specification vendor
java.vm.specification.name	Java virtual machine specification name
java.vm.version	Java Virtual Machine implementation version
java.vm.vendor	Java Virtual Machine implementation vendor
java.vm.name	Java Virtual Machine implementation name
java.specification.version	Java Runtime Environment Standard version
java.specification.vendor	Java Runtime Environment specification vendor
java.specification.name	Java Runtime Environment specification name
java.class.version	Java format version number
java.class.path	Java class path
java.library.path	List of search paths when the library is loaded
java.io.tmpdir	Default temporary file path
java.compiler	Name of the JIT compiler to be used
java.ext.dirs	Path of one or more extended Directories
os.name	Operating system name
os.arch	Operating System Architecture
os.version	Operating system version
file.separator	File separator ("/" in UNIX)
path.separator	Path separator (":" in UNIX)
line.separator	Line separator ("/n" in UNIX ")
user.name	User Account Name
user.home	User's home directory
user.dir	Current working directory of the user

Multiple paths in the system property values are separated by path delimiters of the platform.

Note that even if the security manager does not allow executiongetPropertiesOperation, which may also allow execution
getProperty(String)Operation.

Return Value:

System attributes

Throw:

SecurityException-If the security manager exists and its checkPropertiesAccessThe method does not allow access to system properties.

For more information, see:

setProperties(java.util.Properties), SecurityException, SecurityManager.checkPropertiesAccess(), Properties