正确使用Java -D命令行参数

问题描述

在Java中传递-D参数时，编写命令行然后从代码访问它的正确方法是什么？

例如，我已经尝试过这样写...

   -jar 。请尝试以下方法：
  java -Dtest =true-jar myApplication.jar 
  
 
 
 
从命令行帮助：
  -options] -jar jarfile [args ...] 
  
换句话说，现在将把 -Dtest =true作为传递给 main 的参数之一，而不是作为JVM参数。
 
 
 
（你应该也可以删除引号，但它可能很好工作 - 它可能取决于你的shell。 ）
 
When passing a -D parameter in Java, what is the proper way of writing the command-line and then accessing it from code? 
For example, I have tried writing something like this...
if (System.getProperty("test").equalsIgnoreCase("true"))
{
   //Do something
}
And then calling it like this...
java -jar myApplication.jar -Dtest="true"
But I receive a NullPointerException. What am I doing wrong?
 解决方案 
I suspect the problem is that you've put the "-D" after the -jar. Try this:
java -Dtest="true" -jar myApplication.jar
From the command line help:
java [-options] -jar jarfile [args...]
In other words, the way you've got it at the moment will treat -Dtest="true" as one of the arguments to pass to main instead of as a JVM argument.
(You should probably also drop the quotes, but it may well work anyway - it probably depends on your shell.)
                        
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