使用java中的反射动态实例化类失败

Question

我有一段代码

List<Class<? extends SubApplication>> appClasses = new ArrayList<Class<? extends SubApplication>>();
List<SubApplication> subApps = new ArrayList<SubApplication>();

// instructions filling "appClasses"
// ... other instructions

for (Class<? extends SubApplication> crtClass : appClasses) {
    try {
        Constructor<? extends SubApplication> constructor = crtClass.getConstructor(new Class<?>[] { Application.class });
        SubApplication subApp = constructor.newInstance(this);
        if (!subApps.contains(subApp)) {
            subApps.add(subApp);
        }
    } catch (SecurityException e) {
    } catch (NoSuchMethodException e) {
    } catch (IllegalArgumentException e) {
    } catch (InstantiationException e) {
        System.out.println(e.getMessage());
    } catch (IllegalAccessException e) {
    } catch (InvocationTargetException e) {
    }
}

而this是Application的一个实例。

我有几个SubApplication实现。该类的所有子类都需要实现一个以Application为参数的构造函数，这是约定的一部分。

现在，我总是收到一个InstanciationException，尽管我完全知道子类包含这样的构造函数。关于异常的详细信息不可用：getMessage()返回null

编辑： SubApplication是抽象的。但是appClasses只包含sub-classes of SubApplication

Edit2: --我不得不“构造”堆栈跟踪，因为根据约定，我必须捕获异常。

sun.reflect.InstantiationExceptionConstructorAccessorImpl.newInstance(InstantiationExceptionConstructorAccessorImpl.java:30)
java.lang.reflect.Constructor.newInstance(Constructor.java:513)
ch.migros.gmaare.tk.auth.gui.AuthenticableApp.instanciateSubApps(AuthenticableApp.java:64)
ch.migros.gmaare.tk.auth.gui.AuthenticableApp.<init>(AuthenticableApp.java:42)
ch.migros.gmaare.tk.voicesuite.VoicesuiteApplication.<init>(VoicesuiteApplication.java:34)
sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
java.lang.reflect.Constructor.newInstance(Constructor.java:513)
java.lang.Class.newInstance0(Class.java:355)
java.lang.Class.newInstance(Class.java:308)
com.vaadin.terminal.gwt.server.ApplicationServlet.getNewApplication(ApplicationServlet.java:82)
com.vaadin.terminal.gwt.server.AbstractApplicationServlet.createApplication(AbstractApplicationServlet.java:978)
com.vaadin.terminal.gwt.server.AbstractApplicationServlet.findApplicationInstance(AbstractApplicationServlet.java:801)
com.vaadin.terminal.gwt.server.AbstractApplicationServlet.service(AbstractApplicationServlet.java:456)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:298)
org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:859)
org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:588)
org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
java.lang.Thread.run(Thread.java:662)

任何想法都会受到赞赏。

Answer 1

如评论中所述。我愚蠢到无法验证数组中的类名。实际上，我真的把SubApplication添加到列表中了。无论如何，谢谢你的投入！

Answer 2

当您尝试以下代码时：

import java.lang.reflect.Constructor;

public class Main {

    public static void main( final String[] args ) {
        final Class<? extends A>[] classes = new Class[] { B.class, C.class };
        for ( final Class<? extends A> clazz : classes ) {
            try {
                final Constructor<? extends A> constructor = clazz.getConstructor( null );
                final A a = constructor.newInstance( null );
            } catch ( final Exception e ) {
                e.printStackTrace();
            }
        }
    }

    public static abstract class A {

    }

    public static class B extends A {

    }

    public static abstract class C extends A {

    }
}

您将得到相同的错误：

java.lang.InstantiationException
    at sun.reflect.InstantiationExceptionConstructorAccessorImpl.newInstance(InstantiationExceptionConstructorAccessorImpl.java:30)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
    at Main.main(Main.java:10)

您可以将代码修改为：

if ( Modifier.isAbstract( clazz.getModifiers() ) ) {
    System.out.println( "skipping" );
} else {
    final A a = constructor.newInstance( null );
}