问题描述
Java 是否有一个默认的系统环境变量，当我们设置它时总是会被读取/附加?CATALINA_OTPS/JAVA_OPTS 等似乎只适用于 TOMCAT/JBOSS 等.
Does Java have a default System Environment Variable that will always be read/appended when we set it? CATALINA_OTPS/JAVA_OPTS etc seems only for TOMCAT/JBOSS etc.
- 我不想通过 Java 系统属性(通过 -Dprop1=value1 -Dprop2=value2 传入)设置它，因为它涉及 shell/batch 脚本.
- 它应该可以跨操作系统工作，就像在 Windows 中双击 jar 文件一样.
- 它应该适用于不同的 JRE(Sun、IBM、OpenJDK 等).
- 不应涉及额外的编码.
- 它应该可以在大多数库配置文件中使用，例如设置 log4j级别 ${LOG_LEVEL}.
更新:添加了第 4 项和第 5 项.从标题中删除 OS 以使我的问题更清楚.
Update: Added item # 4 and 5. Remove OS from title to make my question clearer.
Update 2:看了 Perception 的回答后，我的第 2 和第 3 项似乎可以通过 System.getenv 实现.第4、5项如何实现?
Update 2: After looking at Perception's answer, it seems like my item 2 and 3 can be achieved via System.getenv. How to achieve item 4 and 5?
以下是场景示例:现在想象一下，JAVA_DEFAULT_OPTS 是一个环境变量，Java 将读取它，因为它现在已成为标准.在开发台式机上，我设置 JAVA_DEFAULT_OPTS=-DLOG_LEVEL=DEBUG -Xmx384m;在生产服务器机器上，客户设置 JAVA_DEFAULT_OPTS=-DLOG_LEVEL=INFO -Xmx1024m.当我/用户在 Windows 上双击 jar 文件时，应用程序将运行不同的 log4j 级别和最大内存堆大小.
Here is example of scenario:
Imagine now JAVA_DEFAULT_OPTS is an environment variable that will be read by Java as it has now become the standard. On development desktop machine, I set JAVA_DEFAULT_OPTS=-DLOG_LEVEL=DEBUG -Xmx384m; On production server machine, customers set JAVA_DEFAULT_OPTS=-DLOG_LEVEL=INFO -Xmx1024m. When I/users double click the jar file on Windows, the application will run will different log4j level and max memory heap size.
推荐答案
有一个特殊的环境变量叫做_JAVA_OPTIONS，它的值会被JVM(java.exe)拾取.
There is a special environment variable called _JAVA_OPTIONS, its value will be picked up by the JVM (java.exe).
在 Windows 中:
In Windows:
set _JAVA_OPTIONS=-Xms64m -Xmx128m -Dawt.useSystemAAFontSettings=lcd
在 Linux 中:
export _JAVA_OPTIONS='-Xms64m -Xmx128m -Dawt.useSystemAAFontSettings=lcd'
对于 Java Web Start，它是 JAVAWS_VM_ARGS.对于 javaw.exe (Applet)，它是 _JPI_VM_OPTIONS.
For Java Web Start it's JAVAWS_VM_ARGS. For javaw.exe (Applet), it's _JPI_VM_OPTIONS.
编辑 20201213
_JAVA_OPTIONS 环境变量没问题，但没有记录或支持.
_JAVA_OPTIONS environment variable was ok but was not documented or supported.
由于没有标准化，其他供应商都有自己的名称，例如IBM_JAVA_OPTIONS.按照惯例，前导下划线名称是私有的，因此标准化 _JAVA_OPTIONS 的使用并不是一个好主意.
Since it is not standardized, other vendors have their own names e.g. IBM_JAVA_OPTIONS. Leading underscore names are private by convention so it's not a good idea to standardize the usage of _JAVA_OPTIONS.
这就是为什么 JAVA_TOOL_OPTIONS 应该是首选的原因.
That's why JAVA_TOOL_OPTIONS should be the preferred choice.
参考:https://docs.oracle.com/javase/8/docs/platform/jvmti/jvmti.html#tooloptions
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