第九天，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