如何在 Java 中获取系统属性和环境变量的值？
如何获取环境变量的值？
Java 中的 System 类提供了一个名为 System.getenv() 的方法，可以用来获取当前系统中一个环境变量集的值。
语法:
public static String getenv(String key);
where key is the Environment variable
whose values we want
下面的示例说明了如何使用 System.getenv()获取系统环境变量:
例 1:获取特定环境变量的值
// Java program to get the value
// of a specific environment variable
// using System.getenv() method
public class GFG {
public static void main(String[] args)
{
// Get the value of
// the TEMP environment variable
System.out.println(System.getenv("TEMP"));
// Get the value of
// the OS environment variable
System.out.println(System.getenv("OS"));
// Get the value of
// the JAVA_HOME environment variable
System.out.println(System.getenv("JAVA_HOME"));
}
}
输出:
例 2:一次获取所有环境变量的值
// Java program to get the value
// of all environment variables at once
// using System.getenv() method
import java.util.Map;
public class GFG {
public static void main(String[] args)
{
// Get the value of
// all environment variables at once
// and store it in Map
Map<String, String> env
= System.getenv();
for (String envName : env.keySet()) {
System.out.format("%s=%s%n",
envName,
env.get(envName));
}
}
}
输出:
注意:输出将取决于运行上述代码的系统。上面给出了一个示例输出
如何获得系统属性的价值？
Java 中的系统类有两种方法用来读取系统属性:
-
java.lang.System.getProperty(String key): fetches only those properties – values that you will specify using the key(associated to that particular value that you want).
示例:
```java // Java Program illustrating the working // of getProperty(String key) method
import java.lang.*; import java.util.Properties;
public class NewClass { public static void main(String[] args) { // Printing Name of the system property System.out.println("user.dir: " + System.getProperty( "user.dir"));
// Fetches the property set with 'home' key System.out.println("home: " + System.getProperty( "home")); // Resulting in Null as no property is present
// Printing 'name of Operating System' System.out.println("os.name: " + System.getProperty( "os.name"));
// Printing 'JAVA Runtime version' System.out.println("version: " + System.getProperty( "java.runtime.version"));
// Printing 'name' property System.out.println("name: " + System.getProperty( "name")); // Resulting in Null as no property is present } } ```
输出:
```java user.dir: /tmp/hsperfdata_bot home: null os.name: Linux version: 1.8.0_101-b13 name: null
```
-
java.lang.System.getProperty(String key, String definition): helps you to create your own key-value sets that you want.
示例:
```java // Java Program illustrating the working of // getProperty(String key, String definition) method
import java.lang.*; import java.util.Properties;
public class NewClass { public static void main(String[] args) {
// Here key = "Hello" and // System Property = "Geeks" System.out.println("Hello property : " + System.getProperty( "Hello", "Geeks"));
// Here key = "Geek" and // System Property = "For Geeks" System.out.println("System-property :" + System.getProperty( "System", "For Geeks"));
// Here key = "Property" and // System Property = null System.out.println("Property-property :" + System.getProperty( "Property")); } } ```
输出:
```java Hello key property : Geeks System key property :For Geeks Property key property :null
```
-
java.lang.System.getProperties(): fetches all the properties – values that the JVM on your System gets from the Operating System.
示例:
```java // Java Program illustrating the working of // getProperties() method
public class GFG { public static void main(String[] args) {
System.out.println(System.getProperties()) } } ```
输出:
![]()
版权属于：月萌API www.moonapi.com，转载请注明出处
