java运行环境变量及自定义变量

本文主要介绍java运行环境变量的获取，如何读取 env.properties 文件并将自定义变量写入到系统变量；

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

System.getenv() 获取的是操作系统环境变量列表，如下：

 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:Javajdk1.8.0_172jrebin
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-clusterspring_in_action_ecl...
java.runtime.version=1.8.0_172-b11
java.awt.graphicsenv=sun.awt.Win32GraphicsEnvironment
java.endorsed.dirs=D:Javajdk1.8.0_172jrelibendorsed
os.arch=amd64
java.io.tmpdir=C:UserszhangsanAppDataLocalTemp
line.separator=

java.vm.specification.vendor=Oracle Corporation
user.variant=
os.name=Windows 10
sun.jnu.encoding=GBK
java.library.path=D:Javajdk1.8.0_172bin;C:WINDOWSS...
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:Userszhangsan
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:Javajdk1.8.0_172jrelibcharsets...
java.vm.specification.version=1.8
sun.arch.data.model=64
java.home=D:Javajdk1.8.0_172jre
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:Javajdk1.8.0_172jrelibext;C:W...
sun.boot.class.path=D:Javajdk1.8.0_172jrelibresource...
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 

1）新建 env.properties 文件， 填写变量

2）读取 自定义变量文件，env.properties 文件；

// 自定义变量
    public static void main3() {
        Properties envProps = new Properties();
        try {
            // 使用 mybatis Resources工具读取环境属性文件
            envProps.load(Resources.getResourceAsStream("env.properties"));
        } catch (IOException e) {
        }
        // 把自定义变量填充到系统变量 SystemProperties
        envProps.stringPropertyNames().forEach(x->{
            System.getProperties().setProperty(x, envProps.getProperty(x));
        });
        System.out.println(System.getenv());
        System.getProperties().list(System.out);
    }

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-clusterspring_in_action_eclipseMybatisHello3_mapper
java.class.path=D:Javajdk1.8.0_172jrelibcharsets.jar;D:Javajdk1.8.0_172jrelibdeploy.jar;D:Javajdk1.8.0_172jrelibextaccess-bridge-64.jar;D:Javajdk1.8.0_172jrelibextcldrdata.jar;D:Javajdk1.8.0_172jrelibextdnsns.jar;D:Javajdk1.8.0_172jrelibextjaccess.jar;D:Javajdk1.8.0_172jrelibextjfxrt.jar;D:Javajdk1.8.0_172jrelibextlocaledata.jar;D:Javajdk1.8.0_172jrelibextnashorn.jar;D:Javajdk1.8.0_172jrelibextsunec.jar;D:Javajdk1.8.0_172jrelibextsunjce_provider.jar;D:Javajdk1.8.0_172jrelibextsunmscapi.jar;D:Javajdk1.8.0_172jrelibextsunpkcs11.jar;D:Javajdk1.8.0_172jrelibextzipfs.jar;D:Javajdk1.8.0_172jrelibjavaws.jar;D:Javajdk1.8.0_172jrelibjce.jar;D:Javajdk1.8.0_172jrelibjfr.jar;D:Javajdk1.8.0_172jrelibjfxswt.jar;D:Javajdk1.8.0_172jrelibjsse.jar;D:Javajdk1.8.0_172jrelibmanagement-agent.jar;D:Javajdk1.8.0_172jrelibplugin.jar;D:Javajdk1.8.0_172jrelibresources.jar;D:Javajdk1.8.0_172jrelibrt.jar;D:bench-clusterspring_in_action_eclipseMybatisHello3_mappertargetclasses;D:software_clustermvn_repo.m2repositoryorgmybatismybatis3.4.1mybatis-3.4.1.jar;D:software_clustermvn_repo.m2repositorymysqlmysql-connector-java8.0.11mysql-connector-java-8.0.11.jar;D:software_clustermvn_repo.m2repositorycomgoogleprotobufprotobuf-java2.6.0protobuf-java-2.6.0.jar;D:software_clustermvn_repo.m2repositoryorgapachelogginglog4jlog4j-core2.11.0log4j-core-2.11.0.jar;D:software_clustermvn_repo.m2repositoryorgapachelogginglog4jlog4j-api2.11.0log4j-api-2.11.0.jar;D:Program FilesIntelliJ IDEA 2021.1libidea_rt.jar
sun.java.command=com.swjtu.mybatis.main.Main2
file.separator=
file.encoding=UTF-8

1）常用系统变量列表

1. user.dir ，当前项目根目录；
2. java.class.path ，java运行时环境路径；
3. sum.java.command ， 主程序所在类的全限定类名；
4. file.separator， 文件路径分隔符；
5. file.encoding，文件编码；

其中 file.encoding 是通过jvm运行时参数指定的， vm 参数如下：

D:Javajdk1.8.0_172binjava.exe "-javaagent:D:Program FilesIntelliJ IDEA 2021.1libidea_rt.jar=49223:D:Program FilesIntelliJ IDEA 2021.1bin" -Dfile.encoding=UTF-8 -classpath D:Javajdk1.8.0_172jrelibcharsets.jar;D:Javajdk1.8.0_172jrelibdeploy.jar;D:Javajdk1.8.0_172jrelibextaccess-bridge-64.jar;D:Javajdk1.8.0_172jrelibextcldrdata.jar;D:Javajdk1.8.0_172jrelibextdnsns.jar;D:Javajdk1.8.0_172jrelibextjaccess.jar;D:Javajdk1.8.0_172jrelibextjfxrt.jar;D:Javajdk1.8.0_172jrelibextlocaledata.jar;D:Javajdk1.8.0_172jrelibextnashorn.jar;D:Javajdk1.8.0_172jrelibextsunec.jar;D:Javajdk1.8.0_172jrelibextsunjce_provider.jar;D:Javajdk1.8.0_172jrelibextsunmscapi.jar;D:Javajdk1.8.0_172jrelibextsunpkcs11.jar;D:Javajdk1.8.0_172jrelibextzipfs.jar;D:Javajdk1.8.0_172jrelibjavaws.jar;D:Javajdk1.8.0_172jrelibjce.jar;D:Javajdk1.8.0_172jrelibjfr.jar;D:Javajdk1.8.0_172jrelibjfxswt.jar;D:Javajdk1.8.0_172jrelibjsse.jar;D:Javajdk1.8.0_172jrelibmanagement-agent.jar;D:Javajdk1.8.0_172jrelibplugin.jar;D:Javajdk1.8.0_172jrelibresources.jar;D:Javajdk1.8.0_172jrelibrt.jar;D:bench-clusterspring_in_action_eclipseMybatisHello3_mappertargetclasses;D:software_clustermvn_repo.m2repositoryorgmybatismybatis3.4.1mybatis-3.4.1.jar;D:software_clustermvn_repo.m2repositorymysqlmysql-connector-java8.0.11mysql-connector-java-8.0.11.jar;D:software_clustermvn_repo.m2repositorycomgoogleprotobufprotobuf-java2.6.0protobuf-java-2.6.0.jar;D:software_clustermvn_repo.m2repositoryorgapachelogginglog4jlog4j-core2.11.0log4j-core-2.11.0.jar;D:software_clustermvn_repo.m2repositoryorgapachelogginglog4jlog4j-api2.11.0log4j-api-2.11.0.jar com.swjtu.mybatis.main.Main2

即通过 -Dfile.encoding=UTF-8 指定的jvm参数，可以通过 System.getProperties() 获取到；