What is the function and usage of the System.getProperty() method in Java?
The function and use of System.getProperty()
When I look at some codes recently, System.getProperty(), System.load(), System.loadLibrary(), etc. are used in many places
System can have standard input, standard output, and error output streams; access to externally defined properties and environment variables; methods for loading files and libraries; and practical methods System.getProperties for quickly copying part of an array. () can determine the current system properties, and the return value is a Properties;
System.load(String filename)
is equivalent to: System.getProperties().load (String filename) Their function is to load the code file with the specified file name from the local file system as a dynamic library.System.setProperties(Properties propes)
Set system properties to Properties parameters;System. setProperties(String key,String value)
Equivalent to System.getProperties().setProperties(String key,String value): Set the system properties indicated by the specified key
static void | **setProperties**(Properties props) Sets system properties to Properties parameters. |
---|---|
static String | **setProperty**(String key, String value) Sets the system property indicated by the specified key. |
static Properties | **getProperties**() Determine the current system properties. |
---|---|
static String | **getProperty**(String key) Gets the system property indicated by the specified key. |
static String | **getProperty**(String key, String def) Gets the system property described by the specified key. |
setProperties
public static void setProperties(Properties props)
Set the system properties to Properties
First, if there is a security manager, then Call its checkPropertiesAccess
method directly without parameters. This may cause a security exception.
The parameter is the collection of current system properties used by the getProperty(String) method. If the argument is null
, the current set of system properties is ignored.
Parameters: - New system property. SecurityException``checkPropertiesAccess
See also:
public static Properties getProperties()
Determine the current system properties.
First, if there is a security manager, call its checkPropertiesAccess
method directly without parameters. This may cause a security exception.
Return the current system property collection used by the getProperty(String) method as a Properties
object. If there is no current system property collection, create and initialize a system property collection first.
This system property collection always contains values for the following keys:
Description of key-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 Specification 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 specification version |
java.specification.vendor | Java Runtime Environment Specification Vendor |
java.specification.name | Java runtime environment specification name |
java.class.version | Java class format version number |
java.class .path | Java class path |
java.library.path | List of paths searched when loading the library |
java.io.tmpdir | Default temporary file path |
java.compiler | The name of the JIT compiler to use |
java.ext.dirs | The path to one or more extension directories |
os.name | The name of the operating system |
os.arch | The architecture of the operating system |
os.version | Operating system version |
file.separator | File separator ("/" on UNIX systems) |
path.separator | Path separator (":" in UNIX systems) |
line.separator | Line separator (in UNIX systems in "/n") |
user.name | User’s account name |
user.home | User’s home directory |
user.dir | User’s current working directory |
系统属性值中的多个路径是用平台的路径分隔符分隔的。
注意,即使安全管理器不允许执行 getProperties
操作,它可能也会选择允许执行 getProperty(String) 操作。
**返回:**抛出: - 如果安全管理器存在并且其 方法不允许访问系统属性。setProperties(java.util.Properties)SecurityExceptionSecurityManager.checkPropertiesAccess()Properties
Java代码
public class TestSystemGetSet { static{ System.setProperty("DB", "mysql");//可以作为全局变量,在任何地方使用 } public static void main(String[] args) { System.out.println(System.getProperty("os.version")); System.out.println(System.getProperty("java.library.path")); System.out.println(System.getProperty("DB")); } }
输出结果:
10.0
C:\Java\jdk1.8.0_121\bin;C:\WINDOWS\Sun\Java\bin;C:\WINDOWS\system32;C:\WINDOWS;C:/Java/jre8/bin/server;C:/Java/jre8/bin;C:/Java/jre8/lib/amd64;C:\Program Files\IBM\WebSphere MQ\java\lib;C:\Program Files\IBM\WebSphere MQ\java\lib64;E:\app\Administrator\product\11.2.0\dbhome_2\bin;C:\ProgramData\Oracle\Java\javapath;C:\WINDOWS\system32;C:\WINDOWS;C:\WINDOWS\System32\Wbem;C:\WINDOWS\System32\WindowsPowerShell\v1.0\;C:\Program Files\MySQL\MySQL Server 5.1\bin;D:/maven\bin;C:\Program Files (x86)\Rational\common;C:\Program Files\IBM\WebSphere MQ\bin64;C:\Program Files\IBM\WebSphere MQ\bin;C:\Program Files\IBM\WebSphere MQ\tools\c\samples\bin;C:\Java\jdk1.8.0_121\bin;C:\Users\Administrator\AppData\Local\Microsoft\WindowsApps;D:\maven\bin;E:\soft\apache-ant-1.10.1\bin;D:\erl9.2\bin;;C:\Users\Administrator\AppData\Local\Microsoft\WindowsApps;E:\tool\eclipse;;.
mysql
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