方法一:
利用getResources().getIdentifier(String name,String defType,String defPackage) 获取

public int  getResource(String imageName){
     Context ctx=getBaseContext();
     int resId = getResources().getIdentifier(imageName, "mipmap", ctx.getPackageName());
     //如果没有在"mipmap"下找到imageName,将会返回0
     return resId;
}

方法二:
使用反射机制获取

public int getMipmapResource(String imageName) {
        Class mipmap = R.mipmap.class;
        try {
            Field field = mipmap.getField(imageName);
            int resId = field.getInt(imageName);
            return resId;
        } catch (NoSuchFieldException e) {//如果没有在"mipmap"下找到imageName,将会返回0
            return 0;
        } catch (IllegalAccessException e) {
            return 0;
        }
    }