如何访问Android中SDCard内的Java文件

Question

I am trying to load a Java file to my android project using URLClassLoader class.

But I got a ClassNotFoundError when I run the below code:

package com.xyz.abc;
public class ConstantClassReader
{
    public void readFile() throws MalformedURLException
    {
        String url = "file://"+Environment.getExternalStorageDirectory().getPath()+"/StringConstants.class";
        URLClassLoader urlClassLoader = URLClassLoader.newInstance(new URL[]{new URL(url)});
        Class simpleClass = null;
        try {
            simpleClass = urlClassLoader.loadClass("com.xyz.abc.StringConstants");
            Constructor simpleConstructor = simpleClass.getConstructor();
            Object simpleClassObj = simpleConstructor.newInstance();
            Method method = simpleClass.getMethod("myMethod");
            method.invoke(simpleClassObj);
        } catch (ClassNotFoundException | NoSuchMethodException | IllegalAccessException | InstantiationException | InvocationTargetException e) {
            e.printStackTrace();
        }
    }
}

The below Java file is resides inside my SDCard:

package com.xyz.abc;
public class StringConstants{
    public void myMethod(){
        System.out.println("myMethod Loaded");
    }
}

Answer 1

A class loader loads classes .

Putting a Java source file somewhere will not do.

You have to compile that file; and maybe you are lucky then. But I would be rather surprised if the Android JVM allows you to load classes from arbitrary places. This screams: "security problem" all over the place.

Given your requirement, I would suggest a different solution, something on top of ordinary Java properties. Meaning: it seems that you simply want to provide some "configuration" information dynamically to your Java app. Then have that app read a properties file that contains key/value pairs. That is (almost) business as usual; and not leading to a need to load class files in arbitrary places.

Answer 2

http://www.beanshell.org/

you can embed beanshell, load the java file, instance and execute whatever.

access the java file as any other plain file from the sd

How can I read a text file from the SD card in Android?