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``checkPropertiesAccessSee 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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