有没有办法知道一个Java程序是从命令行还是从一个jar文件启动？ [英] Is there a way to know if a Java program was started from the command line or from a jar file?

问题描述

我想在控制台中显示一条消息，或者弹出一个消息，所以如果没有指定参数，我想知道应该显示哪个参数

I want to either display a message in the console or a pop up, so in case a parameter is not specified, I want to know to which should I display

类似：

if( !file.exists() ) {
    if( fromCommandLine()){
        System.out.println("File doesn't exists");
    }else if ( fromDoubleClickOnJar() ) {
        JOptionPane.showMessage(null, "File doesn't exists");
    }
 }

推荐答案

直接的回答是你不能告诉JVM是如何启动的。

The straight forward answer is that you cannot tell how the JVM was launched.

但是对于你的问题中的例子，你不需要知道如何JVM已启动。你真正需要知道的是，用户是否会看到写入控制台的消息。而这样做的方式是这样的：

But for the example use-case in your question, you don't really need to know how the JVM was launched. What you really need to know is whether the user will see a message written to the console. And the way to do that would be something like this:

if (!file.exists()) {
    Console console = System.console();
    if (console != null) {
        console.format("File doesn't exists%n");
    } else if (!GraphicsEnvironment.isHeadless()) {
        JOptionPane.showMessage(null, "File doesn't exists");
    } else {
        // Put it in the log
    }
 }

控制台，而不是水密，强烈暗示控制台对象（如果存在）写入控制台，不能重定向。

The javadoc for Console, while not water tight, strongly hints that a Console object (if it exists) writes to a console and cannot be redirected.

感谢@Stephen Denne ！GraphicsEnvironment.isHeadless（）提示。

Thanks @Stephen Denne for the !GraphicsEnvironment.isHeadless() tip.

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