我还有另一个问题,答案让我无法回避。我希望在运行时从外部jar中获取一个类,并从中获取一个方法并将其传递给一个参数。我目前的代码打开jar并抓住类并运行该方法,但当我尝试并传递给它一个参数时,该方法运行,但我得到一个InvocationTargetException。有任何想法吗?Java在运行时加载外部类
这里是我的代码:
String path = "test.jar";
URL[] classes = {new File(path).toURI().toURL()};
URLClassLoader child = new URLClassLoader (classes, this.getClass().getClassLoader());
try {
Class classToLoad = Class.forName("testClass", true, child);
Method method = classToLoad.getDeclaredMethod ("testMethod", String.class);
Object instance = classToLoad.newInstance();
Object result = method.invoke(instance, new String("Test from method!"));
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (SecurityException e) {
e.printStackTrace();
} catch (NoSuchMethodException e) {
e.printStackTrace();
} catch (InstantiationException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
} catch (IllegalArgumentException e) {
e.printStackTrace();
} catch (InvocationTargetException e) {
e.printStackTrace();
}
这里是它引发的错误:
Test from method!
java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at Load.loadJar(LoadTerrem.java:33)
at Load.<init>(LoadTerrem.java:18)
at Load.main(LoadTerrem.java:13)
Caused by: java.lang.NullPointerException
at MenuSingleplayer.LoadWorlds(MenuSingleplayer.java:210)
at MenuSingleplayer.setup(MenuSingleplayer.java:89)
at M0.LoadGame(M0.java:76)
... 7 more
正如你可以看到,该方法执行,打印出来传递给它的字符串,但随后抛出一个错误就行了:
Object result = method.invoke(instance, new String("Test from LoadTerrem!"));
有什么想法吗?谢谢!
哪一条是第33行? – 2012-03-27 21:41:55