问题描述
我正在尝试构建一个简单的JDBC Spring Template应用程序，我正在使用的Web框架是wicket并且在jetty 6 web服务器下（通过Jetty Maven插件）。另外，我正在用Eclipse构建应用程序。
I am trying to build a simple JDBC Spring Template application, the web framework I am using is wicket and under the jetty 6 web server (through the Jetty Maven Plugin). Also, I am building the app with Eclipse.
出于某种原因，我得到了一个带有Derby jdbc类的NoClassDefFoundError。我假设我会找到一个未找到异常的类，所以我猜其他的事情正在发生。 derby类是类路径的一部分，即WEB-INF / lib目录。您认为这个问题是什么？
For some reason, I am getting a NoClassDefFoundError with the Derby jdbc class. I am assuming I would get a class not found exception was not found, so am guessing something else is happening. The derby class is part of the classpath, the WEB-INF/lib directory. What do you think the issue is?
我对问题的看法：这不是在类路径中找不到jar错误但是更多的是Java或Spring动态加载该类以及何时加载它的问题。
My thoughts on the problem: It is not a "jar not found in the classpath" error but more an issue with Java or spring dynamically loading that class and when it gets loaded.
我使用Eclipse作为开发工具但它可能不是问题的一部分。我仍然在命令行上使用Maven并遇到同样的问题。
I am using Eclipse as the development tool but it probably isn't part of the problem. I am still using Maven on the command line and getting the same issue.
这是错误：
WicketMessage：无法使用构造函数实例化页面public wicketspring.easy.HomePage（）
WicketMessage: Can't instantiate page using constructor public wicketspring.easy.HomePage()
根本原因：
java.lang.NoClassDefFoundError: Could not initialize class org.apache.derby.jdbc.EmbeddedDriver
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:169)
at org.apache.commons.dbcp.BasicDataSource.createDataSource(BasicDataSource.java:1130)
at org.apache.commons.dbcp.BasicDataSource.getConnection(BasicDataSource.java:880)
at org.springframework.jdbc.datasource.DataSourceUtils.doGetConnection(DataSourceUtils.java:113)
at org.springframework.jdbc.datasource.DataSourceUtils.getConnection(DataSourceUtils.java:79)
at org.springframework.jdbc.core.JdbcTemplate.execute(JdbcTemplate.java:577)
at org.springframework.jdbc.core.JdbcTemplate.execute(JdbcTemplate.java:619)
at wicketspring.easy.jdbc.JdbcWicketSpringHandler.data(JdbcWicketSpringHandler.java:39)
at WICKET_wicketspring.easy.jdbc.JdbcWicketSpringHandler$$FastClassByCGLIB$$f1187cb6.invoke(<generated>)
at net.sf.cglib.proxy.MethodProxy.invoke(MethodProxy.java:191)
at org.apache.wicket.proxy.LazyInitProxyFactory$CGLibInterceptor.intercept(LazyInitProxyFactory.java:319)
at WICKET_wicketspring.easy.jdbc.JdbcWicketSpringHandler$$EnhancerByCGLIB$$e8f0e174.data(<generated>)
at wicketspring.easy.HomePage.<init>(HomePage.java:91)
at wicketspring.easy.HomePage.<init>(HomePage.java:47)
这是Spring的applicationContext.xml：
Here is the applicationContext.xml for Spring:
<beans>
<bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource">
<property name="driverClassName" value="org.apache.derby.jdbc.EmbeddedDriver" />
<property name="url"><value>jdbc:derby:wicketspringdb</value></property>
<property name="username"><value></value></property>
<property name="password"><value></value></property>
</bean>
<bean id="jdbcTemplate" class="org.springframework.jdbc.core.JdbcTemplate">
<property name="dataSource" ref="dataSource" />
</bean>
</beans>
<beans>
<import resource="classpath:common.xml"/>
<bean id="jdbcHandler" class=wicketspring.easy.jdbc.JdbcWicketSpringHandler">
<property name="jdbcTemplate" ref="jdbcTemplate" />
</bean>
</beans>
...
Another stack trace system out.
Page.java:74) - At [2b] -- java.lang.NoClassDefFoundError: Could not initialize class org.apache.derby.jdbc.EmbeddedDriver
java.lang.NoClassDefFoundError: Could not initialize class org.apache.derby.jdbc.EmbeddedDriver
at wicketspring.easy.HomePage.<init>(HomePage.java:72)
at wicketspring.easy.HomePage.<init>(HomePage.java:47)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:
39)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorIm
pl.java:27)
...
这是java代码，代码编译，我可以打印出类但我无法实例化它。奇怪？
Here is the java code, the code compiles and I can print out the class but I can't instantiate it. Strange?
Java代码：
package wicketspring.easy;
import java.util.List;
import org.apache.wicket.Application;
import org.apache.wicket.PageParameters;
import org.apache.wicket.markup.html.WebPage;
import org.apache.wicket.markup.html.basic.Label;
import org.apache.wicket.markup.html.list.ListItem;
import org.apache.wicket.markup.html.list.ListView;
import org.apache.wicket.model.CompoundPropertyModel;
import org.apache.wicket.proxy.IProxyTargetLocator;
import org.apache.wicket.proxy.LazyInitProxyFactory;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import model.LoadableDetachableList;
import model.SelectionOptionBean;
import wicketspring.easy.jdbc.JdbcWicketSpringHandler;
import wicketspring.easy.service.IStateListService;
import wicketspring.easy.service.StateListServiceImpl;
import org.apache.derby.jdbc.EmbeddedDriver;
public class HomePage extends WebPage {
private final JdbcWicketSpringHandler jdbcWicketSpringHandler;
public HomePage(final PageParameters parameters) {
super(parameters);
jdbcWicketSpringHandler = (JdbcWicketSpringHandler) LazyInitProxyFactory.createProxy(JdbcWicketSpringHandler.class,
new IProxyTargetLocator() {
private static final long serialVersionUID = 1L;
public Object locateProxyTarget() {
return ((WicketApplication) Application.get()).context().getBean("jdbcHandler");
}
});
/// WEIRD BECAUSE IT REACHES THIS POINT!!!
LOGGER.debug("At [1] -- " + EmbeddedDriver.class);
try {
LOGGER.debug("At [2] -- " + new org.apache.derby.jdbc.EmbeddedDriver());
} catch (NoClassDefFoundError ne) {
// STACK TRACE ERROR HERE!!!!
LOGGER.debug("At [2b] -- " + ne);
ne.printStackTrace();
} catch (Exception e) {
LOGGER.debug("At [2] -- " + e);
e.printStackTrace();
}
try {
LOGGER.debug("At -- " + Class.forName("org.apache.derby.jdbc.EmbeddedDriver"));
} catch (NoClassDefFoundError ne) {
LOGGER.debug("At [3b] -- " + ne);
ne.printStackTrace();
} catch (Exception e) {
LOGGER.debug("At [3] -- " + e);
e.printStackTrace();
}
/// ERROR FOR STACKOVERFLOW IS GENERATED FROM THIS LINE!!!!
LOGGER.debug("At HomePage - jdbcHandler [3]: " + jdbcWicketSpringHandler.toStringJdbcTemplate());
LOGGER.debug("At HomePage - jdbcHandler [3]: " + jdbcWicketSpringHandler.data());
...
} // End of Class //
编辑：
我可能错过了一个jar文件，它是Spring Jdbc或dbcp的依赖项。
I might be missing a jar file that is a dependency of Spring Jdbc or dbcp.
这是我的WEB-INF / lib上市：
Here is my WEB-INF/lib listing:
antlr-2.7.6.jar
aopalliance-1.0.jar
avalon-framework-4.1.3.jar
axis-1.4.jar
axis-jaxrpc-1.4.jar
cglib-nodep-2.2.jar
commons-collections-3.1.jar
commons-dbcp-1.2.2.jar
commons-logging-1.1.jar
commons-pool-1.3.jar
derby-10.6.1.0.jar
dom4j-1.6.1.jar
hibernate-core-3.5.1-Final.jar
jetty-6.1.4.jar
jetty-management-6.1.4.jar
jetty-util-6.1.4.jar
jta-1.1.jar
log4j-1.2.14.jar
logkit-1.0.1.jar
mx4j-3.0.1.jar
mx4j-tools-3.0.1.jar
servlet-api-2.5-6.1.4.jar
servlet-api-2.5.jar
slf4j-api-1.5.8.jar
slf4j-log4j12-1.4.2.jar
spring-2.5.6.jar
spring-aop-2.5.6.jar
spring-beans-2.5.6.jar
spring-context-2.5.6.jar
spring-core-2.5.6.jar
spring-jdbc-2.5.6.jar
spring-test-2.5.6.jar
spring-tx-2.5.6.jar
testRunWrapper-1.0.0.jar
wicket-1.4.13.jar
wicket-ioc-1.4.13.jar
wicket-spring-1.4.13.jar
xml-apis-1.0.b2.jar
推荐答案
所以'无法初始化类org.apache.derby.jdbc.EmbeddedDriver'错误实际上是其他一些不太明显的类加载问题的主要症状。
So the 'Could not initialize class org.apache.derby.jdbc.EmbeddedDriver' error was actually the main symptom of some other, less obvious, class loading issues.
我正在使用Jetty作为Web服务器，Spring作为java6下的框架。
I was using Jetty as the web server and Spring as the framework under java6.
我认为有一个类加载问题，与MBeanServer类有关。
I believe there was a class loading issue, related to the MBeanServer class.
我确实忽略了启动时发生的错误：引起：java.lang.LinkageError：加载器约束违规：加载器（org / mortbay / jetty / webapp / WebAppClassLoader的实例）之前启动的加载用于java.lang.ClassLoader.defineClass1（Native M ethod）
at java.lang.ClassLoader.defineClassCond（ClassLoader.java:632）
at java.lang.ClassLoader.defineClass（ClassLoader.java:616)
at java.security.SecureClassLoader .defineClass（SecureClassLoader.java:141）
And I did ignore an error that happened at startup: "Caused by: java.lang.LinkageError: loader constraint violation: loader (instance of org/mortbay/jetty/webapp/WebAppClassLoader) previously initiated loading for a different type with name "javax/management/MBeanServer" at java.lang.ClassLoader.defineClass1(Native Method) at java.lang.ClassLoader.defineClassCond(ClassLoader.java:632) at java.lang.ClassLoader.defineClass(ClassLoader.java:616) at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:141)"
我在WEB-INF / lib目录中搜索了该类。它作为mx4j：jar的一部分包含在内。 Mx4j是jetty-management.jar的依赖项。我真的不需要jetty-management，所以我从我的pom文件中删除了该引用。
I searched for the class in my WEB-INF/lib directory. It was included as part of mx4j:jar. Mx4j was a dependency for jetty-management.jar. I didn't really need jetty-management so I removed that reference from my pom file.
基本上包含MBeanServer（来自mx4j）会导致某种类加载问题无法正确加载org.apache.derby.jdbc.EmbeddedDriver。我从我的Web应用程序中删除了它，应用程序开始正常工作。
Basically the inclusion of MBeanServer (from mx4j) caused some kind of class loading issue where org.apache.derby.jdbc.EmbeddedDriver couldn't be loaded properly. I removed it from my web application and the application started working properly.
这篇关于在Web环境Spring / Wicket / Derby / Jetty中出现NoClassDefFoundError错误的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！