loadClass基本流程

/*** Loads the class with the specified <a href="#name">binary name</a>. The*/ protected Class<?> loadClass(String name, boolean resolve) throws ClassNotFoundException {// First, check if the class has already been loadedClass<?> 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; } 復(fù)制代碼

可以看出loadClass的基本流程如下：

首先判斷是否已經(jīng)加載過class，如果加載過，就直接返回對(duì)應(yīng)的Class<?>對(duì)象；如果沒有加載過，就查找它的父類是否加載過，如果父類加載過，就返回；如果父類未加載過，就自己去加載。

Android應(yīng)用中ClassLoader對(duì)象

public class MainActivity extends AppCompatActivity {private static final String TAG = MainActivity.class.getSimpleName();@Overrideprotected 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());}}} } 復(fù)制代碼

我們創(chuàng)建一個(gè)Android項(xiàng)目，在Activity的onCreate方法中打印ClassLoader的值，如上。

打印結(jié)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 復(fù)制代碼

由打印日志可以看出，此App包含了兩種ClassLoader，一個(gè)是PathClassLoader，一個(gè)是BootClassLoader。

BootClassLoader是系統(tǒng)啟動(dòng)時(shí)創(chuàng)建的,用于加載Android FrameWork層的class；PathClassLoader是在App啟動(dòng)時(shí)創(chuàng)建的，用于加載該App中的class文件。

ClassLoader的作用

1，共享作用：類加載過，后面用到時(shí)就不用再加載。

2，隔離作用：不同繼承路線的類加載器，加載的類一定是不同的。

DexClassLoader與PathClassLoader異同點(diǎn)

DexClassLoader和PathClassLoader都是繼承BaseDexClassLoader。

DexClassLoader：可加載jar/dex/apk，也可以加載SD卡中未安裝的apk。

PathClassLoader：只可加載系統(tǒng)中已經(jīng)安裝的apk。

轉(zhuǎn)載于:https://juejin.im/post/5cd27a51f265da036c57a096

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