從不同罐子中加載同一個類

Question

我有一個新的小Swing項目，我需要從兩個不同的罐子中加載同一個類，這些罐子是第三方，所以我沒有源代碼。

例如我需要從兩個罐子中加載myClass。 jar1.jar jar2.jar

只是我什麼，我需要做的：

public void doMyClassLogicVersion1() { 

    Loader = // here i need to load jar1.myClass. 
    // myClass need a two params to initialize it in the normal case 
    // also i need to access its static members 
    // do the logic of myClass version1 

} 

public void doMyClassLogicVersion2() { 

    Loader = // here i need to load jar2.myClass. 
    // myClass need a two params to initialize it in the normal case 
    // also i need to access its static members 
    // do the logic of myClass version2 
} 

這樣我可以做到這一點，我知道這是不好，但我真的需要。

Answer 1

您可以加載新的代碼轉換成新的類加載器相對容易：

案例1：如果你的類在當前的背景下，通用父接口（或類），例如Runnable接口，您可以使用此代碼：

public void doMyClassLogicVersion1() { 
    ClassLoader loader = URLClassLoader.newInstance(
    new URL[] { yourURL1 }, 
    getClass().getClassLoader() 
    ); 
    Class<?> clazz = Class.forName("mypackage.MyClass", true, loader); 
    Class<? extends Runnable> runClass = clazz.asSubclass(Runnable.class); 
    // Avoid Class.newInstance, for it is evil. 
    Constructor<? extends Runnable> ctor = runClass.getConstructor(); 
    Runnable doRun = ctor.newInstance(); 
    doRun.run(); 
} 

public void doMyClassLogicVersion2() { 
    ClassLoader loader = URLClassLoader.newInstance(
    new URL[] { yourURL2 }, 
    getClass().getClassLoader() 
    ); 
    Class<?> clazz = Class.forName("mypackage.MyClass", true, loader); 
    Class<? extends Runnable> runClass = clazz.asSubclass(Runnable.class); 
    // Avoid Class.newInstance, for it is evil. 
    Constructor<? extends Runnable> ctor = runClass.getConstructor(); 
    Runnable doRun = ctor.newInstance(); 
    doRun.run(); 
} 

案例2：如果類並不共享共同的父：

public void doMyClassLogicVersion1() { 
    ClassLoader loader = URLClassLoader.newInstance(
    new URL[] { yourURL1 }, 
    getClass().getClassLoader() 
    ); 
    Class<?> clazz = Class.forName("mypackage.MyClass", true, loader); 
    // Avoid Class.newInstance, for it is evil. 
    Constructor<?> ctor = runClass.getConstructor(); 
    Object obj = ctor.newInstance(); 

    String methodName = "getName"; 

    java.lang.reflect.Method method; 
    try { 
     method = clazz.getMethod(methodName, param1.class, param2.class, ..); 
    } catch (SecurityException e) { 
     // ... 
    } catch (NoSuchMethodException e) { 
     // ... 
    } 

    try { 
     method.invoke(obj, arg1, arg2,...); 
    } catch (IllegalArgumentException e) { 
     // ... 
    } catch (IllegalAccessException e) { 
     // ... 
    } catch (InvocationTargetException e) { 
     // ... 
    } 
} 

public void doMyClassLogicVersion2() { 
    ClassLoader loader = URLClassLoader.newInstance(
    new URL[] { yourURL2 }, 
    getClass().getClassLoader() 
    ); 
    Class<?> clazz = Class.forName("mypackage.MyClass", true, loader); 
    // Avoid Class.newInstance, for it is evil. 
    Constructor<?> ctor = runClass.getConstructor(); 
    Object obj = ctor.newInstance(); 

    String methodName = "getName"; 

    java.lang.reflect.Method method; 
    try { 
     method = clazz.getMethod(methodName, param1.class, param2.class, ..); 
    } catch (SecurityException e) { 
     // ... 
    } catch (NoSuchMethodException e) { 
     // ... 
    } 

    try { 
     method.invoke(obj, arg1, arg2,...); 
    } catch (IllegalArgumentException e) { 
     // ... 
    } catch (IllegalAccessException e) { 
     // ... 
    } catch (InvocationTargetException e) { 
     // ... 
    } 
} 

Answer 2

是的，你可以做到。爲避免出現問題，我建議您不要將任何jar放在常規CLASSPATH中，創建2個不同的線程，並在啓動它們之前將每個線程的ContextClassLoader設置爲相應的jar。