loadClass基本流程
/** * Loads the class with the specified binary name. The */protected Class loadClass(String name, boolean resolve) throws ClassNotFoundException{ // First, check if the class has already been loaded Class c = findLoadedClass(name); if (c == null) { try { if (parent != null) { c = parent.loadClass(name, false); } else { c = findBootstrapClassOrNull(name); } } catch (ClassNotFoundException e) { // ClassNotFoundException thrown if class not found // from the non-null parent class loader } if (c == null) { // If still not found, then invoke findClass in order // to find the class. c = findClass(name); } } return c;}复制代码
可以看出loadClass的基本流程如下:
首先判断是否已经加载过class,如果加载过,就直接返回对应的Class<?>对象;如果没有加载过,就查找它的父类是否加载过,如果父类加载过,就返回;如果父类未加载过,就自己去加载。
Android应用中ClassLoader对象
public class MainActivity extends AppCompatActivity { private static final String TAG = MainActivity.class.getSimpleName(); @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); printClassLoaders(); setContentView(R.layout.activity_main); } private void printClassLoaders() { ClassLoader classLoader = getClassLoader(); if (classLoader != null) { Log.e(TAG, "Current ClassLoader is: " + classLoader.toString()); while (classLoader.getParent() != null) { classLoader = classLoader.getParent(); Log.e(TAG, "ClassLoader's parent is: " + classLoader.toString()); } } }}复制代码
我们创建一个Android项目,在Activity的onCreate方法中打印ClassLoader的值,如上。
打印结果如下:
2019-04-30 18:52:53.219 16456-16456/com.my.classloaderdemo E/MainActivity: Current ClassLoader is: dalvik.system.PathClassLoader[ DexPathList[ [ zip file "/data/app/com.my.classloaderdemo-faSliZa20JPLlSUl0kPawg==/base.apk", zip file "/data/app/com.my.classloaderdemo-faSliZa20JPLlSUl0kPawg==/split_lib_dependencies_apk.apk", zip file "/data/app/com.my.classloaderdemo-faSliZa20JPLlSUl0kPawg==/split_lib_resources_apk.apk", zip file "/data/app/com.my.classloaderdemo-faSliZa20JPLlSUl0kPawg==/split_lib_slice_0_apk.apk", zip file "/data/app/com.my.classloaderdemo-faSliZa20JPLlSUl0kPawg==/split_lib_slice_1_apk.apk", zip file "/data/app/com.my.classloaderdemo-faSliZa20JPLlSUl0kPawg==/split_lib_slice_2_apk.apk", zip file "/data/app/com.my.classloaderdemo-faSliZa20JPLlSUl0kPawg==/split_lib_slice_3_apk.apk", zip file "/data/app/com.my.classloaderdemo-faSliZa20JPLlSUl0kPawg==/split_lib_slice_4_apk.apk", zip file "/data/app/com.my.classloaderdemo-faSliZa20JPLlSUl0kPawg==/split_lib_slice_5_apk.apk", zip file "/data/app/com.my.classloaderdemo-faSliZa20JPLlSUl0kPawg==/split_lib_slice_6_apk.apk", zip file "/data/app/com.my.classloaderdemo-faSliZa20JPLlSUl0kPawg==/split_lib_slice_7_apk.apk", zip file "/data/app/com.my.classloaderdemo-faSliZa20JPLlSUl0kPawg==/split_lib_slice_8_apk.apk", zip file "/data/app/com.my.classloaderdemo-faSliZa20JPLlSUl0kPawg==/split_lib_slice_9_apk.apk" ], nativeLibraryDirectories=[/data/app/com.my.classloaderdemo-faSliZa20JPLlSUl0kPawg==/lib/x86, /system/lib, /vendor/lib ] ] ]2019-04-30 18:52:53.219 16456-16456/com.my.classloaderdemo E/MainActivity: ClassLoader's parent is: java.lang.BootClassLoader@c8bb22f复制代码
由打印日志可以看出,此App包含了两种ClassLoader,一个是PathClassLoader,一个是BootClassLoader。
BootClassLoader是系统启动时创建的,用于加载Android FrameWork层的class;PathClassLoader是在App启动时创建的,用于加载该App中的class文件。
ClassLoader的作用
1,共享作用:类加载过,后面用到时就不用再加载。
2,隔离作用:不同继承路线的类加载器,加载的类一定是不同的。
DexClassLoader与PathClassLoader异同点
DexClassLoader和PathClassLoader都是继承BaseDexClassLoader。
DexClassLoader:可加载jar/dex/apk,也可以加载SD卡中未安装的apk。
PathClassLoader:只可加载系统中已经安装的apk。