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

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

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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