如何根据用例从Java加载本机库？

Question

I have a use-case depending on which I want to load libraries.

if(useCase) {
  Static { System.loadLibrary("a") };
}
else {
  Static { System.loadLibrary("b") }; 
}

Till now, I had just one library to load so I was loading it static in the class declaration but now I have this use-case and depending on it I need to load the library.

I was trying to load the library in the constructor only but any static declaration inside a constructor is not allowed, and I am confused what other ways are there by which I can achieve the same?

I want to load the libraries as static only. Any help would be appreciated.

Answer 1

Please use custom class loader. below is the link for more info http://tutorials.jenkov.com/java-reflection/dynamic-class-loading-reloading.html

Answer 2

It is easy to call loadLibrary() from static {} (class) constructor, because this way you ensure that the code that implements native methods of your class, is available when the classloader needs it to initialize the class, like here:

public class ClassWithNativeMethods {
    static {
        System.loadLibrary("a");
    }
    native void method1();
}

class ClassThatUsesClassWithNativeMethods {
    ClassWithNativeMethods field = new ClassWithNativeMethods();
}

If your Java has two different scenarios that involve loading different native libraries, you can load this library before loading this class:

public class ClassWithNativeMethods {
    native void method1();
}

class ClassThatUsesClassWithNativeMethods {
    ClassWithNativeMethods field;

    public ClassThatUsesClassWithNativeMethods(bool useCase) {
        if (useCase) {
            System.loadLibrary("a");
        }
        else {
            System.loadLibrary("b");
        }
        field = new ClassWithNativeMethods();
    }
}

If the condition is static , you can use it inside static constructor:

public class ClassWithNativeMethods {
    static {
        if (BuildConfig.useCase) {
            System.loadLibrary("a");
        else {
            System.loadLibrary("b");
        }
    }
    native void method1();
}