// java.util.Properties 1.0
Properties()
// 创建一个空的属性映射

Properties(Properties default)
// 创建一个带有一组默认值的空的属性映射

String getProperty(String key)
// 获取属性的对应关系，返回键key对应的属性值（String字符串）。如果映射不存在，返回默认表中与这个key对应的字符串

String getProperty(String key, String defaultValues)
// 获得在键找到时具有的默认值属性，返回与键key对应属性值（String字符串）。如果映射不存在，返回默认字符串

void load(InputStream in)
// 从InputStream加载属性映射

void store(OutputStream out, String commentString)
// 把属性保存到OutputStream

Properties settings = new Properties();
// 写属性映射
settings.setProperty("username", "张三");
settings.setProperty("age", "20");

// 读取属性映射
String name = settings.getProperty("username");
String age = settings.getProperty("age");

// 测试 - 打印读取的属性映射
System.out.println(name);
System.out.println(age);

// 保存属性映射settings到文件"program.properties"     
OutputStream out = new FileOutputStream("program.properties");
        settings.store(out, "Program Properties");


// UTF-8 编码方式保存属性映射settings到文件"program.properties"  
        OutputStreamWriter out = new OutputStreamWriter(new FileOutputStream("program.properties"), "UTF-8");
        settings.store(out, "Program Properties");

#Program Properties
#Fri Jan 08 17:38:39 CST 2021
age=20
username=\u5F20\u4E09

// 具体编码方式一般根据实际情况选择, 保存的时候用的什么编码方式, 加载的时候就用同样编码方式
// 从文件加载属性映射到settings
InputStream in = new FileInputStream("program.properties");
settings.load(in);

// 以utf-8编码方式, 从文件加载到属性映射settings
InputStreamReader in2 = new InputStreamReader(new FileInputStream("program.properties"), "UTF-8");
settings.load(in2);

// 读取属性映射
String name = settings.getProperty("username");
String age = settings.getProperty("age");

// 测试 - 打印读取的属性映射
System.out.println(name);
System.out.println(age);

/**
 * Determines the current system properties.
 * <p>
 * First, if there is a security manager, its
 * <code>checkPropertiesAccess</code> method is called with no
 * arguments. This may result in a security exception.
 * <p>
 * The current set of system properties for use by the
 * {@link #getProperty(String)} method is returned as a
 * <code>Properties</code> object. If there is no current set of
 * system properties, a set of system properties is first created and
 * initialized. 
 * ...
 */

public static Properties getProperties() {
　　SecurityManager sm = getSecurityManager();
   if (sm != null) {
   　　sm.checkPropertiesAccess();
   }

   return props;
}

Properties props = System.getProperties();

props.getProperty("java.version");

public static void main(String[] args) {
    Properties props = System.getProperties();//系统属性
    System.out.println("Java的运行环境版本：" + props.getProperty("java.version"));
    System.out.println("Java的运行环境供应商：" + props.getProperty("java.vendor"));
    System.out.println("Java供应商的URL：" + props.getProperty("java.vendor.url"));
    System.out.println("Java的安装路径：" + props.getProperty("java.home"));
    System.out.println("Java的虚拟bai机规范版本：" + props.getProperty("java.vm.specification.version"));
    System.out.println("Java的虚拟机规范供应商：" + props.getProperty("java.vm.specification.vendor"));
    System.out.println("Java的虚拟机规范名称：" + props.getProperty("java.vm.specification.name"));
    System.out.println("Java的虚拟机实现版本：" + props.getProperty("java.vm.version"));
    System.out.println("Java的虚拟机实现供应商：" + props.getProperty("java.vm.vendor"));
    System.out.println("Java的虚拟机实现名称：" + props.getProperty("java.vm.name"));
    System.out.println("Java运行时环境规范版本：" + props.getProperty("java.specification.version"));
    System.out.println("Java运行时环境规范供应商：" + props.getProperty("java.specification.vender"));
    System.out.println("Java运行时环境规范名称：" + props.getProperty("java.specification.name"));
    System.out.println("Java的类格式版本号：" + props.getProperty("java.class.version"));
    System.out.println("Java的类路径：" + props.getProperty("java.class.path"));
    System.out.println("加载库时搜索的路径列表：" + props.getProperty("java.library.path"));
    System.out.println("默认的临时文件路径：" + props.getProperty("java.io.tmpdir"));
    System.out.println("一个或多个扩展目录的路径：" + props.getProperty("java.ext.dirs"));
    System.out.println("操作系统的名称：" + props.getProperty("os.name"));
    System.out.println("操作系统的构架：" + props.getProperty("os.arch"));
    System.out.println("操作系统的版本：" + props.getProperty("os.version"));
    System.out.println("文件分隔符：" + props.getProperty("file.separator")); //unix是"/" , Windows是 "\"
    System.out.println("路径分隔符：" + props.getProperty("path.separator")); //unix是＂:＂, windows是 ";"
    System.out.println("行分隔符：" + props.getProperty("line.separator"));   //unix是＂\n＂, windows是 "\r\n"
    System.out.println("用户的账户名称：" + props.getProperty("user.name"));
    System.out.println("用户的主目录：" + props.getProperty("user.home"));
    System.out.println("用户的当前工作目录：" + props.getProperty("user.dir"));

}

Java的运行环境版本：1.8.0_181
Java的运行环境供应商：Oracle Corporation
Java供应商的URL：http://java.oracle.com/
Java的安装路径：C:\Program Files\Java\jdk1.8.0_181\jre
Java的虚拟bai机规范版本：1.8
Java的虚拟机规范供应商：Oracle Corporation
Java的虚拟机规范名称：Java Virtual Machine Specification
Java的虚拟机实现版本：25.181-b13
Java的虚拟机实现供应商：Oracle Corporation
Java的虚拟机实现名称：Java HotSpot(TM) 64-Bit Server VM
Java运行时环境规范版本：1.8
Java运行时环境规范供应商：null
Java运行时环境规范名称：Java Platform API Specification
Java的类格式版本号：52.0
Java的类路径：C:\Program Files\Java\jdk1.8.0_181\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\rt.jar;F:\workspace\IDEA\Java_Core2\out\production\Java_Core2;E:\Program Files\JetBrains\IntelliJ IDEA 202002\lib\idea_rt.jar
加载库时搜索的路径列表：C:\Program Files\Java\jdk1.8.0_181\bin;C:\WINDOWS\Sun\Java\bin;C:\WINDOWS\system32;C:\WINDOWS;E:\Python\Python37\Scripts\;E:\Python\Python37\;C:\Program Files (x86)\Common Files\Oracle\Java\javapath;C:\WINDOWS\system32;C:\WINDOWS;C:\WINDOWS\System32\Wbem;C:\WINDOWS\System32\WindowsPowerShell\v1.0\;C:\Program Files\Java\jdk1.8.0_181\bin;C:\WINDOWS\System32\OpenSSH\;C:\Program Files\dotnet\;C:\Program Files (x86)\National Instruments\Shared\LabVIEW CLI;E:\Program Files\TortoiseGit\bin;E:\Program Files\Git\cmd;E:\Program Files\TortoiseSVN\bin;E:\MinGW\bin;C:\Program Files\Intel\WiFi\bin\;C:\Program Files\Common Files\Intel\WirelessCommon\;E:\Program Files\UltraEdit;C:\Program Files\Java\jdk1.8.0_181\jre\bin;C:\Program Files\MySQL\MySQL Shell 8.0\bin\;C:\Program Files\Intel\WiFi\bin\;C:\Program Files\Common Files\Intel\WirelessCommon\;C:\Users\Martin\AppData\Local\Microsoft\WindowsApps;E:\Programs\Microsoft VS Code\bin;E:\Program Files (x86)\SSH Communications Security\SSH Secure Shell;E:\Program Files\JetBrains\IntelliJ IDEA 2020.2\bin;;;.
默认的临时文件路径：C:\Users\Martin\AppData\Local\Temp\
一个或多个扩展目录的路径：C:\Program Files\Java\jdk1.8.0_181\jre\lib\ext;C:\WINDOWS\Sun\Java\lib\ext
操作系统的名称：Windows 10
操作系统的构架：amd64
操作系统的版本：10.0
文件分隔符：\
路径分隔符：;
行分隔符：

用户的账户名称：Martin
用户的主目录：C:\Users\Martin
用户的当前工作目录：F:\workspace\IDEA\Java_Core2

System.getProperties() .list(System.out);