System类获取系统环境变量和系统参数

import java.util.Enumeration;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Properties;
import java.util.Set;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.util.Collection;
import java.io.FileOutputStream;

/**
* Description:
* System类的一些方法的使用
*
* @author Lee
* */
public class Demo {

/**
* Description;
* 获取系统的环境变量
* */
public static void test1(){

/*
public static Map<String,String> getenve()
Returns an unmodfiable string map view of the current system environment.

public static String getenv(String name)
Gets the value of the specified environment variable.
*/
//获取系统地环境变量的Map集合
Map<String,String> map = System.getenv();

//第一种方法迭代Map的方法,获取键的Set集合
Set<String> keySet = map.keySet();
for(Iterator interator=keySet.iterator();interator.hasNext();){
String key = (String)interator.next();
System.out.println(key+" = "+map.get(key));
}
System.out.println("----------------------------------------------");

//第二种迭代Map的方法，获取value的Collection集合
Collection<String> values = map.values();
for(Iterator iterator  =  values.iterator();iterator.hasNext();){
String value = (String)iterator.next();
System.out.println(value);
}
System.out.println("----------------------------------------------");

//第三种迭代Map的方法，获取键-值得Map.Entry集合
Set<Entry<String,String>> entrySet = map.entrySet();
for(Iterator iterator = entrySet.iterator();iterator.hasNext();){
Entry<String,String> entry = (Entry<String,String>)iterator.next();
System.out.println(entry.getKey()+" = "+entry.getValue());

}

/*
public static Properties getProperties()
->Dtermines the current system properties

public static String getProperties(String key)
->Gets the system property indicated by the specified key.

public static String getProperties(String key,String default);
Returns:the string value of the system property, or the default
value if there is no property with that key.
*/

//获取系统参数
Properties ps = System.getProperties();
//System.out.println(System.getProperties());
//System.getProperty("sdfsd");
//System.getProperty("dfsdf","default");

/*
An object that implements the Enumeration interface generates a
series of elements, one at a time. Successive calls to the nextElement
method return successive elements of the series.
*/
Enumeration enumeration = ps.propertyNames();
while(enumeration.hasMoreElements()){
String str = (String)enumeration.nextElement();
System.out.println(str+" = "+ps.getProperty(str));
}
}
public static void main(String[] args) {
}
}

附记：

系统参数：

Key Description of Associated Value

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.vendo—->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 to search when loading libraries

java.io.tmpdir—->Default temp file path

java.compiler—->Name of JIT compiler to use

java.ext.dirs—->Path of extension directory or directories Deprecated. This property, and the mechanism which implements it, may be removed in a future release.

os.name—->Operating system name

os.arch Operating—->system architecture

os.version—->Operating system version

file.separator—->File separator (“/” on UNIX)

path.separator—->Path separator (“:” on UNIX)

line.separator—->Line separator (“\n” on UNIX)

user.name—->User’s account name

user.home—->User’s home directory

user.dir—->User’s current working directory