//得到application对象
ApplicationInfo appInfo = getApplicationInfo();
//得到该图片的id(name 是该图片的名字，"drawable" 是该图片存放的目录，appInfo.packageName是应用程序的包)
int resID = getResources().getIdentifier(name, "drawable", appInfo.packageName);
//代码如下
public Bitmap getRes(String name) {
ApplicationInfo appInfo = getApplicationInfo();
int resID = getResources().getIdentifier(name, "drawable", appInfo.packageName);
return BitmapFactory.decodeResource(getResources(), resID);
}

String path = "com/xiangmu/test.png"; //图片存放的路径
InputStream is = getClassLoader().getResourceAsStream(path); //得到图片流