【README】

本文主要介紹java運行環境變量的獲取，如何讀取 env.properties 文件并將自定義變量寫入到系統變量；

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【1】System.getenv() 獲取環境變量

public static void main1() {Map<String, String> envMap = System.getenv();envMap.entrySet().forEach(x-> System.out.println(x.getKey() + "=" + x.getValue()));}

System.getenv() 獲取的是操作系統環境變量列表，如下：

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【2】 System.getProperties()獲取java運行時環境變量

public static void main2() {Properties props = System.getProperties();props.list(System.out);} -- listing properties -- java.runtime.name=Java(TM) SE Runtime Environment sun.boot.library.path=D:\Java\jdk1.8.0_172\jre\bin java.vm.version=25.172-b11 java.vm.vendor=Oracle Corporation java.vendor.url=http://java.oracle.com/ path.separator=; java.vm.name=Java HotSpot(TM) 64-Bit Server VM file.encoding.pkg=sun.io user.script= user.country=CN sun.java.launcher=SUN_STANDARD sun.os.patch.level= java.vm.specification.name=Java Virtual Machine Specification user.dir=D:\bench-cluster\spring_in_action_ecl... java.runtime.version=1.8.0_172-b11 java.awt.graphicsenv=sun.awt.Win32GraphicsEnvironment java.endorsed.dirs=D:\Java\jdk1.8.0_172\jre\lib\endorsed os.arch=amd64 java.io.tmpdir=C:\Users\zhangsan\AppData\Local\Temp\ line.separator=java.vm.specification.vendor=Oracle Corporation user.variant= os.name=Windows 10 sun.jnu.encoding=GBK java.library.path=D:\Java\jdk1.8.0_172\bin;C:\WINDOWS\S... java.specification.name=Java Platform API Specification java.class.version=52.0 sun.management.compiler=HotSpot 64-Bit Tiered Compilers os.version=10.0 user.home=C:\Users\zhangsan user.timezone= java.awt.printerjob=sun.awt.windows.WPrinterJob file.encoding=UTF-8 java.specification.version=1.8 user.name=zhangsan java.class.path=D:\Java\jdk1.8.0_172\jre\lib\charsets... java.vm.specification.version=1.8 sun.arch.data.model=64 java.home=D:\Java\jdk1.8.0_172\jre sun.java.command=com.swjtu.mybatis.main.Main2 java.specification.vendor=Oracle Corporation user.language=zh awt.toolkit=sun.awt.windows.WToolkit java.vm.info=mixed mode java.version=1.8.0_172 java.ext.dirs=D:\Java\jdk1.8.0_172\jre\lib\ext;C:\W... sun.boot.class.path=D:\Java\jdk1.8.0_172\jre\lib\resource... java.vendor=Oracle Corporation file.separator=\ java.vendor.url.bug=http://bugreport.sun.com/bugreport/ sun.cpu.endian=little sun.io.unicode.encoding=UnicodeLittle sun.desktop=windows sun.cpu.isalist=amd64zheshi

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【3】自定義變量

1）新建 env.properties 文件， 填寫變量

2）讀取 自定義變量文件，env.properties 文件；

// 自定義變量public static void main3() {Properties envProps = new Properties();try {// 使用 mybatis Resources工具讀取環境屬性文件envProps.load(Resources.getResourceAsStream("env.properties"));} catch (IOException e) {}// 把自定義變量填充到系統變量 SystemPropertiesenvProps.stringPropertyNames().forEach(x->{System.getProperties().setProperty(x, envProps.getProperty(x));});System.out.println(System.getenv());System.getProperties().list(System.out);}

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【4】幾個常用系統變量

Properties sysProps = System.getProperties(); System.out.println("user.dir=" + sysProps.getProperty("user.dir")); System.out.println("java.class.path=" + sysProps.getProperty("java.class.path")); System.out.println("sun.java.command=" + sysProps.getProperty("sun.java.command")); System.out.println("file.separator=" + sysProps.getProperty("file.separator")); System.out.println("file.encoding=" + sysProps.getProperty("file.encoding")); user.dir=D:\bench-cluster\spring_in_action_eclipse\MybatisHello3_mapper java.class.path=D:\Java\jdk1.8.0_172\jre\lib\charsets.jar;D:\Java\jdk1.8.0_172\jre\lib\deploy.jar;D:\Java\jdk1.8.0_172\jre\lib\ext\access-bridge-64.jar;D:\Java\jdk1.8.0_172\jre\lib\ext\cldrdata.jar;D:\Java\jdk1.8.0_172\jre\lib\ext\dnsns.jar;D:\Java\jdk1.8.0_172\jre\lib\ext\jaccess.jar;D:\Java\jdk1.8.0_172\jre\lib\ext\jfxrt.jar;D:\Java\jdk1.8.0_172\jre\lib\ext\localedata.jar;D:\Java\jdk1.8.0_172\jre\lib\ext\nashorn.jar;D:\Java\jdk1.8.0_172\jre\lib\ext\sunec.jar;D:\Java\jdk1.8.0_172\jre\lib\ext\sunjce_provider.jar;D:\Java\jdk1.8.0_172\jre\lib\ext\sunmscapi.jar;D:\Java\jdk1.8.0_172\jre\lib\ext\sunpkcs11.jar;D:\Java\jdk1.8.0_172\jre\lib\ext\zipfs.jar;D:\Java\jdk1.8.0_172\jre\lib\javaws.jar;D:\Java\jdk1.8.0_172\jre\lib\jce.jar;D:\Java\jdk1.8.0_172\jre\lib\jfr.jar;D:\Java\jdk1.8.0_172\jre\lib\jfxswt.jar;D:\Java\jdk1.8.0_172\jre\lib\jsse.jar;D:\Java\jdk1.8.0_172\jre\lib\management-agent.jar;D:\Java\jdk1.8.0_172\jre\lib\plugin.jar;D:\Java\jdk1.8.0_172\jre\lib\resources.jar;D:\Java\jdk1.8.0_172\jre\lib\rt.jar;D:\bench-cluster\spring_in_action_eclipse\MybatisHello3_mapper\target\classes;D:\software_cluster\mvn_repo\.m2\repository\org\mybatis\mybatis\3.4.1\mybatis-3.4.1.jar;D:\software_cluster\mvn_repo\.m2\repository\mysql\mysql-connector-java\8.0.11\mysql-connector-java-8.0.11.jar;D:\software_cluster\mvn_repo\.m2\repository\com\google\protobuf\protobuf-java\2.6.0\protobuf-java-2.6.0.jar;D:\software_cluster\mvn_repo\.m2\repository\org\apache\logging\log4j\log4j-core\2.11.0\log4j-core-2.11.0.jar;D:\software_cluster\mvn_repo\.m2\repository\org\apache\logging\log4j\log4j-api\2.11.0\log4j-api-2.11.0.jar;D:\Program Files\IntelliJ IDEA 2021.1\lib\idea_rt.jar sun.java.command=com.swjtu.mybatis.main.Main2 file.separator=\ file.encoding=UTF-8

1）常用系統變量列表

user.dir ，當前項目根目錄；

java.class.path ，java運行時環境路徑；

sum.java.command ， 主程序所在類的全限定類名；

file.separator， 文件路徑分隔符；

file.encoding，文件編碼；

其中 file.encoding 是通過jvm運行時參數指定的， vm 參數如下：

D:\Java\jdk1.8.0_172\bin\java.exe "-javaagent:D:\Program Files\IntelliJ IDEA 2021.1\lib\idea_rt.jar=49223:D:\Program Files\IntelliJ IDEA 2021.1\bin" -Dfile.encoding=UTF-8 -classpath D:\Java\jdk1.8.0_172\jre\lib\charsets.jar;D:\Java\jdk1.8.0_172\jre\lib\deploy.jar;D:\Java\jdk1.8.0_172\jre\lib\ext\access-bridge-64.jar;D:\Java\jdk1.8.0_172\jre\lib\ext\cldrdata.jar;D:\Java\jdk1.8.0_172\jre\lib\ext\dnsns.jar;D:\Java\jdk1.8.0_172\jre\lib\ext\jaccess.jar;D:\Java\jdk1.8.0_172\jre\lib\ext\jfxrt.jar;D:\Java\jdk1.8.0_172\jre\lib\ext\localedata.jar;D:\Java\jdk1.8.0_172\jre\lib\ext\nashorn.jar;D:\Java\jdk1.8.0_172\jre\lib\ext\sunec.jar;D:\Java\jdk1.8.0_172\jre\lib\ext\sunjce_provider.jar;D:\Java\jdk1.8.0_172\jre\lib\ext\sunmscapi.jar;D:\Java\jdk1.8.0_172\jre\lib\ext\sunpkcs11.jar;D:\Java\jdk1.8.0_172\jre\lib\ext\zipfs.jar;D:\Java\jdk1.8.0_172\jre\lib\javaws.jar;D:\Java\jdk1.8.0_172\jre\lib\jce.jar;D:\Java\jdk1.8.0_172\jre\lib\jfr.jar;D:\Java\jdk1.8.0_172\jre\lib\jfxswt.jar;D:\Java\jdk1.8.0_172\jre\lib\jsse.jar;D:\Java\jdk1.8.0_172\jre\lib\management-agent.jar;D:\Java\jdk1.8.0_172\jre\lib\plugin.jar;D:\Java\jdk1.8.0_172\jre\lib\resources.jar;D:\Java\jdk1.8.0_172\jre\lib\rt.jar;D:\bench-cluster\spring_in_action_eclipse\MybatisHello3_mapper\target\classes;D:\software_cluster\mvn_repo\.m2\repository\org\mybatis\mybatis\3.4.1\mybatis-3.4.1.jar;D:\software_cluster\mvn_repo\.m2\repository\mysql\mysql-connector-java\8.0.11\mysql-connector-java-8.0.11.jar;D:\software_cluster\mvn_repo\.m2\repository\com\google\protobuf\protobuf-java\2.6.0\protobuf-java-2.6.0.jar;D:\software_cluster\mvn_repo\.m2\repository\org\apache\logging\log4j\log4j-core\2.11.0\log4j-core-2.11.0.jar;D:\software_cluster\mvn_repo\.m2\repository\org\apache\logging\log4j\log4j-api\2.11.0\log4j-api-2.11.0.jar com.swjtu.mybatis.main.Main2

即通過 -Dfile.encoding=UTF-8 指定的jvm參數，可以通過 System.getProperties() 獲取到；

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