Question

我有一个新的小Swing项目，我需要从两个不同的jarsm加载相同的类这些罐子是第三方所以我没有源代码。

例如我需要从两个罐子加载myClass。 jar1.jar jar2.jar

简直就是我需要做的事情：

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
}

我也可以这样做，我知道这不好，但我真的需要。

Answer 1

您可以相对轻松地将新代码加载到新的类加载器中：

案例1：如果您的类在当前上下文中具有公共父接口（或类），例如Runnable，则可以使用以下代码：

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：如果班级不共享共同的父母：

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。为避免出现问题，我建议您不要将任何jar放入常规CLASSPATH中，创建2个不同的线程，并在启动它们之前将每个线程的ContextClassLoader设置为相应的jar。

从不同的罐子装载相同的类

2 个答案: