Java 动态 Class 在 webapp 中加载

Question

我做了一个java项目，项目只包含这个class:

package test.processor;

public abstract class Processor {

    public abstract void loadData(String objectId);
    public abstract void processData();
    public abstract void saveData(String objectId);

}

项目导出为 jar 文件(processor.jar)

然后我做了另一个导入 processor.jar 的项目，并且有一个 class 扩展了 Processor:

package test.process;

import test.processor.Processor;

public class Process extends Processor{

    @Override
    public void loadData(String objectId) {
        System.out.println("LOAD DATAAAAAAAAAAAA");     
    }

    @Override
    public void processData() {
        System.out.println("PROCESS DATAAAAAAAAAAAA");
    }

    @Override
    public void saveData(String objectId) {
        System.out.println("SAVE DATAAAAAAAAAAAA");
    }

}

该项目也导出为 jar (plugin.jar)。

最后，我编写了一些代码来动态加载插件：

import test.processor.Processor;

public class Test {

    public void testPlugins(){

        Processor plugin = (Processor) loadJar(
                "C:\Users\...\Desktop\plugin.jar",
                "test.process.Process");
        processor.loadData("dada");

    }

    private Object loadJar(String jar, String className){

        File jarFile = new File(jar);
        Object instance = null;
        try {
            URL jarpath = jarFile.toURI().toURL();
            String jarUrl = "jar:" + jarpath + "!/";
            URL urls[] = { new URL(jarUrl) };
            URLClassLoader child = new URLClassLoader(urls);
            Class classToLoad = Class.forName(nomeClasse, true, child);
            instance = classToLoad.newInstance();
        } catch (Exception ex) {
            ex.printStackTrace();
        }
        return instance;

    }


}

如果我运行 main 方法中的代码它工作正常，一旦我尝试运行它在服务器中加载 class 时出现问题，我得到ClassNotFoundException（处理器）。我尝试将罐子放入 tomcat/lib、project/WEB-INF/lib，但没有任何变化。

知道我做错了什么吗？

Answer 1

我没有按我想要的方式解决，但是我解决了：

首先，我尝试手动加载 process.jar：

private Object loadJars(String processJar, String pluginJar, String className){

    File processJarFile = new File(processJar);
    File pluginJarFile = new File(pluginJar);


    Object instance = null;
    try {

        URL processJarPath = processJarFile.toURI().toURL();
        String processJarUrl = "jar:" + processJarPath + "!/";

        URL pluginJarPath = pluginJarFile.toURI().toURL();
        String pluginJarUrl = "jar:" + pluginJarPath + "!/";


        URL urls[] = { new URL(processJarUrl), new URL(pluginJarUrl) };
        URLClassLoader child = new URLClassLoader(urls);
        Class classToLoad = Class.forName(nomeClasse, true, child);
        instance = classToLoad.newInstance();
    } catch (Exception ex) {
        ex.printStackTrace();
    }
    return instance;

}

正确加载进程 class，问题发生在 testPlugins 方法中，一旦它尝试转换为处理器（ClassCastException，无法将进程转换为处理器）：

public void testPlugins(){

    Processor plugin = (Processor) loadJars("C:\Users\...\Desktop\processor.jar",
            "C:\Users\...\Desktop\plugin.jar",
            "test.process.Process");
    processor.loadData("dada");

}

仍然需要阅读很多关于 classloading 的内容，但我想问题是它无法识别从 C:\Users\...\Desktop\processor.jar 加载的处理器与从 webapp 上下文加载的处理器相同，或者它 "forgets" Process extends Processor.

赶时间没时间研究，为了解决问题我用反射调用了方法：

public void modifiedTestPlugins(){

    Object plugin = loadJar("C:\Users\...\Desktop\processor.jar",
            "C:\Users\...\Desktop\plugin.jar",
            "test.process.Process");

    try {
        Method processData = findMethod(obj.getClass(), "processData");

        //here I invoke the processData method, it prints: PROCESS DATAAAAAAAAAAAA
        loadData.invoke(processData, new Object[]{});
    } catch (Exception e) {
        e.printStackTrace();
    }

}

private static Method findMethod(Class clazz, String methodName) throws Exception {
    Method[] methods = clazz.getMethods();
    for (int i = 0; i < methods.length; i++) {
        if (methods[i].getName().equals(methodName))
            return methods[i];
    }
    return null;
}

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