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我对 Spring 在 Eclipse OSGi 容器中的类加载行为感到有些困惑（这是我试图在其上运行的 TIBCO ActiveMatrix 运行时的基础），并将其归结为以下简单示例。

在其中（TestComponent 对象是在 OSGi 包的 Activator 类中创建和调用的，但我认为这在这里并不重要）我首先直接创建一个对象，只是为了仔细检查它的类是否存在并且可以实例化. 这当然可以按预期工作......其次，我想使用 Spring（正如我最初的意图）创建同一个类的第二个对象，但这会因 ClassNotFoundException 而失败。

Spring 声称，它找不到那个类（即使包和类名肯定匹配），所以我什至添加了一个 .setClassLoader(...) 调用来传递刚刚成功加载相同类的相同类加载器，但 Spring 仍然无法找到该类。任何线索为什么会这样？我已经没有想法了。我错过了什么？

稍后编辑：我只需要意识到，崩溃的不是 ...getBean(...) 方法调用，而是 ClassPathXmlApplicationContext() 构造函数。即，对象已经在该构造函数中创建，并且不仅在随后的 getBean(...) 方法调用中创建。因此，我尝试传入类加载器是徒劳的，因为它已经来晚了。所以问题是：如何将上下文的类加载器传递给该构造函数（或工厂或 Spring 在内部使用的任何东西来创建 ClassPathXmlApplicationContext 对象）？

我的例子：

我首先为要通过 Spring 创建的类定义了一个接口：

package com.example.some_package_0;    
public interface SomeInterface 
{
    public String getSomeString();
}

...和一个类，实现这个接口：

package com.example.some_package_1;

import com.example.some_package_0.SomeInterface;

public class SomeClassA implements SomeInterface
{
    private String someProperty;

    public void setSomeProperty(String someProperty) {
        this.someProperty = someProperty;
    }
    public String getSomeString() {
        return this.someProperty;
    }
}

我的测试程序读取

public class TestComponent 
{
    import com.example.some_package_0.SomeInterface;
    import com.example.some_package_1.SomeClassA;

    public void test() {
        SomeClassA obj1 = new SomeClassA();
        obj1.setSomeProperty("SomeClassA-object (directly created)");
        System.out.println("@@ message=\"" + obj1.getSomeString() + "\"");          

        ClassPathXmlApplicationContext applicationContext;          
        applicationContext = new ClassPathXmlApplicationContext("/META-INF/package1_beans.xml");
        applicationContext.setClassLoader(Thread.currentThread().getContextClassLoader());
        SomeInterface obj2 = (SomeInterface) applicationContext.getBean("bean1");
        System.out.println("@@ message=\"" + obj2.getSomeString() + "\"");
    }
}

正在使用的 /META-INF/package1_beans.xml 内容如下：

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.springframework.org/schema/beans classpath:/org/springframework/beans/factory/xml/spring-beans-2.5.xsd">

    <bean id="bean1" class="com.example.some_package_1.SomeClassA">
        <property name="someProperty"><value>SomeClassA-object (created via Spring)</value></property>
    </bean>
</beans>

异常内容如下：

org.springframework.beans.factory.CannotLoadBeanClassException: Cannot find class [com.example.some_package_1.SomeClassA] for bean with name 'bean1' defined in class path resource [META-INF/package1_beans.xml]; nested exception is java.lang.ClassNotFoundException: com.example.some_package_1.SomeClassA
    at org.springframework.beans.factory.support.AbstractBeanFactory.resolveBeanClass(AbstractBeanFactory.java:1141)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.predictBeanType(AbstractAutowireCapableBeanFactory.java:524)
    at org.springframework.beans.factory.support.AbstractBeanFactory.isFactoryBean(AbstractBeanFactory.java:1177)
    at org.springframework.beans.factory.support.AbstractBeanFactory.isFactoryBean(AbstractBeanFactory.java:758)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:422)
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:728)
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:380)
    at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:139)
    at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:83)
    at com.example.test_spring_example.TestComponent.testOperation(TestComponent.java:71)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at com.tibco.amf.platform.runtime.componentframework.internal.proxies.operation.OperationHandler.invokeMethodWithThreadContext(OperationHandler.java:667)
    at com.tibco.amf.platform.runtime.componentframework.internal.proxies.operation.AsyncToSyncOperationHandler.invoke(AsyncToSyncOperationHandler.java:98)
    at com.tibco.amf.platform.runtime.componentframework.internal.proxies.ProxyInvocationHandlerRegistry$ProxyInvocationContext.invoke(ProxyInvocationHandlerRegistry.java:411)
    at $Proxy67.invoke(Unknown Source)
    at com.tibco.amf.binding.soap.runtime.transport.http.SoapHttpInboundEndpoint.processHttpPost(SoapHttpInboundEndpoint.java:565)
    at com.tibco.amf.binding.soap.runtime.transport.http.SoapHttpServer.doPost(SoapHttpServer.java:195)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:710)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
    at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:502)
    at org.mortbay.jetty.servlet.ServletHandler$Chain.doFilter(ServletHandler.java:1213)
    at com.tibco.governance.pa.amxcomponent.pep.http.HttpPepFilter.doFilter(HttpPepFilter.java:126)
    at org.mortbay.jetty.servlet.ServletHandler$Chain.doFilter(ServletHandler.java:1205)
    at com.tibco.amf.implementation.common.httpfilter.GenericComponentFilter.doFilter(GenericComponentFilter.java:65)
    at org.mortbay.jetty.servlet.ServletHandler$Chain.doFilter(ServletHandler.java:1205)
    at com.tibco.amf.hpa.tibcohost.jetty.internal.ConnectorFilter.doFilter(ConnectorFilter.java:49)
    at org.mortbay.jetty.servlet.ServletHandler$Chain.doFilter(ServletHandler.java:1205)
    at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:388)
    at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
    at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:182)
    at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:765)
    at org.mortbay.jetty.handler.ContextHandlerCollection.handle(ContextHandlerCollection.java:230)
    at org.mortbay.jetty.handler.HandlerCollection.handle(HandlerCollection.java:114)
    at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
    at org.mortbay.jetty.Server.handle(Server.java:326)
    at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:536)
    at org.mortbay.jetty.HttpConnection$RequestHandler.content(HttpConnection.java:928)
    at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:747)
    at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:218)
    at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:405)
    at org.mortbay.jetty.bio.SocketConnector$Connection.run(SocketConnector.java:228)
    at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
    at java.lang.Thread.run(Thread.java:662)
Caused by: java.lang.ClassNotFoundException: com.example.some_package_1.SomeClassA
    at org.eclipse.osgi.internal.loader.BundleLoader.findClassInternal(BundleLoader.java:513)
    at org.eclipse.osgi.internal.loader.BundleLoader.findClass(BundleLoader.java:429)
    at org.eclipse.osgi.internal.loader.BundleLoader.findClass(BundleLoader.java:417)
    at org.eclipse.osgi.internal.baseadaptor.DefaultClassLoader.loadClass(DefaultClassLoader.java:107)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
    at org.springframework.util.ClassUtils.forName(ClassUtils.java:211)
    at org.springframework.beans.factory.support.AbstractBeanDefinition.resolveBeanClass(AbstractBeanDefinition.java:385)
    at org.springframework.beans.factory.support.AbstractBeanFactory.resolveBeanClass(AbstractBeanFactory.java:1138)
    ... 46 more
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2 回答 2

3

实际上，解决方案几乎是微不足道的！正如我在对@Robin 的评论中已经说过的，显然在 OSGi 中，当前线程的类加载器和当前上下文或类的类加载器是不一样的！

所以，我最后要做的就是将当前线程的上下文类加载器设置为调用对象的类加载器，就是这样！也就是说，甚至不需要深入研究 OSGi 来获取包的类加载器或摆弄清单或 POM 或类似的东西 - 只需告诉 Spring 使用“我的”自己的类的类加载器，然后就可以了！

     ...
        // need to set the context class loader to "my" class loader to make Spring work:
        Thread.currentThread().setContextClassLoader(this.getClass().getClassLoader());         
        ClassPathXmlApplicationContext applicationContext;          
        applicationContext =
            new ClassPathXmlApplicationContext("/META-INF/package1_beans.xml");
        SomeInterface obj2 = (SomeInterface) applicationContext.getBean("bean1");
        System.out.println("@@ message=\"" + obj2.getSomeString() + "\"");
     ...

而且 - 是的 - 之后可能应该将线程的类加载器设置回原始值，以防万一 - 所以另一个好用于 try { ... } finally { ... } 子句。:-)

感谢大家的回复！M。

于 2013-01-10T18:08:59.847 回答
0

我还有一个想法。

而不是手动初始化您的 Spring 上下文。尝试将此添加到您的 pom.xml 中（如果您使用的是 Maven）：

<configuration>
    <instructions>
        <Spring-Context>spring/*.xml</Spring-Context>

使其指向您的 applContext 的位置。这似乎也是一种更简洁的连接方式。如果您不使用 Maven，则需要手动添加到清单中，我不确定正确的语法

于 2013-01-10T11:04:46.993 回答