1). Android中类加载器

Android 中常用的类加载器有DexClassLoader和PathClassLoader，其中PathClassLoader是Android应用中的默认加载器。

• DexClassLoader可以加载任何路径下的apk/dex/jar/zip
• PathClassLoader只能加载/data/app中的apk,也就是已经安装在手机中的apk。

2). DexClassLoader

构造方法：

  public DexClassLoader(String dexPath, String optimizedDirectory, String librarySearchPath, ClassLoader parent) ;

其中：

• 继承自BaseDexClassLoader
• dexPath: 加载apk/dex/jar/zip的路径
• optimizedDirectory: 是dex的输出路径
• librarySearchPath: 加载时候需要用到的lib库，一般不用
• parent: DexClassLoader指定的父加载器

3). PathClassLoader

构造方法：

public PathClassLoader(String dexPath, ClassLoader parent);
public PathClassLoader(String dexPath, String librarySearchPath, ClassLoader parent);

其中

• 继承自BaseDexClassLoader
• dexPath: 加载dex路径
• librarySearchPath: 加载时候需要用到的lib库
• parent: PathClassLoader指定的父加载器
• dex释放路径: /data/dalvik-cache

4). 查看各种类加载器

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    
    printMoreClassLoader();
  }
  
  private static final String TAG = "MainActivity";
  /**
   * 打印各种类加载器
   */
  private void printMoreClassLoader() {
    Log.d(TAG, "Context类的类加载器：" + Context.class.getClassLoader());
    Log.d(TAG, "ListView类的类加载器：" + ListView.class.getClassLoader());
    Log.d(TAG, "应用程序默认的类加载器：" + getClassLoader());
    Log.d(TAG, "系统类加载器：" + ClassLoader.getSystemClassLoader());
    Log.d(TAG, "系统类加载器和Context类的类加载器是否相等：" + (Context.class.getClassLoader() ==ClassLoader.getSystemClassLoader()));
    Log.d(TAG, "系统类加载器和应用程序默认加载器是否相等：" + (getClassLoader() == ClassLoader.getSystemClassLoader()));
  
    Log.d(TAG, "================================================");
    
    Log.d(TAG, "打印应用程序默认加载器的委派机制：");
    ClassLoader classLoader = getClassLoader();
    while (null != classLoader) {
      Log.d(TAG, "类加载器： " + classLoader);
      classLoader = classLoader.getParent();
    }
  
    Log.d(TAG, "================================================");
    
    Log.d(TAG, "打印系统加载器的委派机制：");
    classLoader = ClassLoader.getSystemClassLoader();
    while (null != classLoader) {
      Log.d(TAG, "类加载器：" + classLoader);
      classLoader = classLoader.getParent();
    }
    
  }

打印结果：

Context类的类加载器：java.lang.BootClassLoader@8b6e11e
ListView类的类加载器：java.lang.BootClassLoader@8b6e11e
应用程序默认的类加载器：dalvik.system.PathClassLoader[DexPathList[[zip file "/data/app/com.mazaiting.dynamicjar-2/base.apk", zip file "/data/app/com.mazaiting.dynamicjar-2/split_lib_dependencies_apk.apk", zip file "/data/app/com.mazaiting.dynamicjar-2/split_lib_slice_0_apk.apk", zip file "/data/app/com.mazaiting.dynamicjar-2/split_lib_slice_1_apk.apk", zip file "/data/app/com.mazaiting.dynamicjar-2/split_lib_slice_2_apk.apk", zip file "/data/app/com.mazaiting.dynamicjar-2/split_lib_slice_3_apk.apk", zip file "/data/app/com.mazaiting.dynamicjar-2/split_lib_slice_4_apk.apk", zip file "/data/app/com.mazaiting.dynamicjar-2/split_lib_slice_5_apk.apk", zip file "/data/app/com.mazaiting.dynamicjar-2/split_lib_slice_6_apk.apk", zip file "/data/app/com.mazaiting.dynamicjar-2/split_lib_slice_7_apk.apk", zip file "/data/app/com.mazaiting.dynamicjar-2/split_lib_slice_8_apk.apk", zip file "/data/app/com.mazaiting.dynamicjar-2/split_lib_slice_9_apk.apk"],nativeLibraryDirectories=[/data/app/com.mazaiting.dynamicjar-2/lib/arm64, /system/lib64, /vendor/lib64]]]
系统类加载器：dalvik.system.PathClassLoader[DexPathList[[directory "."],nativeLibraryDirectories=[/system/lib64, /vendor/lib64, /system/lib64, /vendor/lib64]]]
系统类加载器和Context类的类加载器是否相等：false
系统类加载器和应用程序默认加载器是否相等：false
================================================
打印应用程序默认加载器的委派机制：
类加载器： dalvik.system.PathClassLoader[DexPathList[[zip file "/data/app/com.mazaiting.dynamicjar-2/base.apk", zip file "/data/app/com.mazaiting.dynamicjar-2/split_lib_dependencies_apk.apk", zip file "/data/app/com.mazaiting.dynamicjar-2/split_lib_slice_0_apk.apk", zip file "/data/app/com.mazaiting.dynamicjar-2/split_lib_slice_1_apk.apk", zip file "/data/app/com.mazaiting.dynamicjar-2/split_lib_slice_2_apk.apk", zip file "/data/app/com.mazaiting.dynamicjar-2/split_lib_slice_3_apk.apk", zip file "/data/app/com.mazaiting.dynamicjar-2/split_lib_slice_4_apk.apk", zip file "/data/app/com.mazaiting.dynamicjar-2/split_lib_slice_5_apk.apk", zip file "/data/app/com.mazaiting.dynamicjar-2/split_lib_slice_6_apk.apk", zip file "/data/app/com.mazaiting.dynamicjar-2/split_lib_slice_7_apk.apk", zip file "/data/app/com.mazaiting.dynamicjar-2/split_lib_slice_8_apk.apk", zip file "/data/app/com.mazaiting.dynamicjar-2/split_lib_slice_9_apk.apk"],nativeLibraryDirectories=[/data/app/com.mazaiting.dynamicjar-2/lib/arm64, /system/lib64, /vendor/lib64]]]
类加载器： java.lang.BootClassLoader@8b6e11e
================================================
打印系统加载器的委派机制：
类加载器：dalvik.system.PathClassLoader[DexPathList[[directory "."],nativeLibraryDirectories=[/system/lib64, /vendor/lib64, /system/lib64, /vendor/lib64]]]
类加载器：java.lang.BootClassLoader@8b6e11e