如何从运行时设置Java jvm属性

Question

I have tried the following code but java still says it cannot find the values. It only works if I set them in JVM before I even run my code. I just want to load them using a properties file. In my case file is being loaded put java properties is not being populated.

Properties prop = new Properties();
    InputStream in = MyClass.class.getResourceAsStream("/vars.options");
    prop.load(in);
    in.close();
    System.setProperties(prop);

Answer 1

Your code doesn't set the properties object to the system properties.

You are missing:

System.setProperties(prop);

Note

Make sure to use a try / catch / finally statement and to close your stream in the finally block.

Alternatively, you can use Java 7's "try-with-resources" idiom, as InputStream is AutoCloseable .

Example (Java 7 style)

try (InputStream in = Main.class.getResourceAsStream("/vars.options")){
    Properties prop = new Properties();
    prop.load(in);
    System.setProperties(prop);
}
catch (IOException ioe) {
    // TODO handle
}
System.out.println(System.getProperty("my.key"));

If in your src root folder, the vars.options file contains:

my.key=foo

...

This will print:

foo