反射时Java参数类型不匹配

Java argument type mismatch while reflection

提问by Artemkller545

I am trying to run some method I load from another jar, that returns an integer, and then I want to return it to another class and pass it to my logic.

我正在尝试运行从另一个 jar 加载的一些方法，该方法返回一个整数，然后我想将其返回到另一个类并将其传递给我的逻辑。

I made my method loading class pretty simple like this:

我使我的方法加载类非常简单，如下所示：

public class ModuleLoader {

    private Class<?> cls;

    public void initializeCommandModule(Module m) throws Exception {
        URL url = this.getURL(m.getJar());
        this.cls = this.loadClass(m.getMainClass(), url);
    }

    public int execute(Module m, ArrayList<String> args) throws Exception {
        Method method = this.cls.getDeclaredMethod("execute", ArrayList.class);
        return (int) method.invoke(this.cls.newInstance(), 1);
    }

    public int respond(ArrayList<String> args) throws Exception {
        Method method = this.cls.getDeclaredMethod("response", ArrayList.class);
        return (int) method.invoke(this.cls.newInstance(), 1);
    }

    private Class<?> loadClass(String cls, URL url) throws ClassNotFoundException, IOException {
        URLClassLoader loader = new URLClassLoader(new URL[]{url});
        Class<?> toReturn = loader.loadClass(cls);
        loader.close();

        return toReturn;
    }

    private URL getURL(String jar) throws MalformedURLException {
        return new File(jar).toURI().toURL();
    }

}

Take a look at the execute(Module m, ArrayList<String> args)method, this line throws the error:

看一下execute(Module m, ArrayList<String> args)方法，这行抛出错误：

    return (int) method.invoke(this.cls.newInstance());

The jar library I load looks like this:

我加载的 jar 库如下所示：

public class Test {

    public int execute(ArrayList<String> i) {
        System.out.println("Hello world!");
        return 0;
    }

}

Why when I run that method I get the following exception thrown?

为什么当我运行该方法时会抛出以下异常？

Exception in thread "main" java.lang.IllegalArgumentException: argument type mismatch
    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 ben.console.modules.ModuleLoader.execute(ModuleLoader.java:24)
    at ben.console.CommandProcessor.process(CommandProcessor.java:37)
    at ben.console.Console.listen(Console.java:25)
    at ben.console.Console.main(Console.java:31)

Thanks in advice!

谢谢指教！

采纳答案by Mena

You forgot to pass an argument to your method invocation.

您忘记将参数传递给您的方法调用。

return (int) method.invoke(this.cls.newInstance(), myArrayList);

You can also invoke with a null argument:

您还可以使用空参数进行调用：

return (int) method.invoke(this.cls.newInstance(), (Object[])null);

回答by Elliott Frisch

In your execute()method, you have this

在你的execute()方法中，你有这个

return (int) method.invoke(this.cls.newInstance());

I think you wanted

我想你想要

return (int) method.invoke(this, args);

Likewise with respond(),

同样respond()，

Method method = this.cls.getDeclaredMethod("response", ArrayList.class);
return (int) method.invoke(this.cls.newInstance(), 1);

should be

应该

return (int) method.invoke(this, args);

You may find my blog post herehelpful.

你可能会发现我的博客文章在这里很有帮助。

回答by AlexR

As far as I understand you fetch method that accepts one argument of type ArrayList:

据我了解，您 fetch 方法接受一个类型的参数ArrayList：

Method method = this.cls.getDeclaredMethod("execute", ArrayList.class);

But then try to invoke it with argument of type that I cannot recognize that is obviously not ArrayList

但是然后尝试使用我无法识别的类型参数来调用它，这显然不是 ArrayList

(int) method.invoke(this.cls.newInstance()); 

What is the type of this.cls.newInstance()? Value of clsis assigned in method initializeCommandModule()as following:

的类型是this.cls.newInstance()什么？的值cls在方法中赋值initializeCommandModule()如下：

this.cls = this.loadClass(m.getMainClass(), url);

this.cls = this.loadClass(m.getMainClass(), url);

where mis Module. I have no idea what Moduleis and therefore do not know what does getMainClass()return.

哪里m是Module。我不知道是什么Module，因此不知道getMainClass()返回什么。

回答by jyllana24

You can also try to convert it into integer. I am having the same issue and I have been pulling off my hair. Using Integer.parseInt it did the trick. I hope this will help.

您也可以尝试将其转换为整数。我有同样的问题，我一直在拔头发。使用 Integer.parseInt 它做到了。我希望这将有所帮助。

Here is a sample code:

这是一个示例代码：

String num = "1";
int result = Integer.parseInt(num);         
System.out.println(result);