Develop Reference

Issue with xss-sanitizer plugin in grails 3.3.x

I am using grails-xss-sanitizer in my grails application in v3.2.11. When I tried to upgrade my application to the latest 3.3.4. It reported below issue:
[2018-04-11 11:16:37,627] [main] ERROR o.s.b.SpringApplication -
Application startup failed java.lang.NoClassDefFoundError:
org/springframework/boot/context/embedded/FilterRegistrationBean
at grails.plugin.xss.sanitizer.XssSanitizerGrailsPlugin$_doWithSpring_closure1.doCall(XssSanitizerGrailsPlugin.groovy:38)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.springsource.loaded.ri.ReflectiveInterceptor.jlrMethodInvoke(ReflectiveInterceptor.java:1427)
at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:98)
at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:325)
at org.codehaus.groovy.runtime.metaclass.ClosureMetaClass.invokeMethod(ClosureMetaClass.java:264)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1034)
at groovy.lang.Closure.call(Closure.java:418)
at groovy.lang.Closure.call(Closure.java:412)
at grails.spring.BeanBuilder.invokeBeanDefiningClosure(BeanBuilder.java:759)
at grails.spring.BeanBuilder.beans(BeanBuilder.java:588)
at grails.spring.BeanBuilder.invokeMethod(BeanBuilder.java:531)
at org.grails.plugins.DefaultGrailsPlugin.doWithRuntimeConfiguration(DefaultGrailsPlugin.java:559)
at org.grails.plugins.AbstractGrailsPluginManager.doRuntimeConfiguration(AbstractGrailsPluginManager.java:167)
at grails.boot.config.GrailsApplicationPostProcessor.postProcessBeanDefinitionRegistry(GrailsApplicationPostProcessor.groovy:171)
at org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanDefinitionRegistryPostProcessors(PostProcessorRegistrationDelegate.java:272)
at org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(PostProcessorRegistrationDelegate.java:122)
at org.springframework.context.support.AbstractApplicationContext.invokeBeanFactoryPostProcessors(AbstractApplicationContext.java:687)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:525)
at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.refresh(EmbeddedWebApplicationContext.java:122)
at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:693)
at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:360)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:303)
at grails.boot.GrailsApp.run(GrailsApp.groovy:84)
at grails.boot.GrailsApp.run(GrailsApp.groovy:393)
at grails.boot.GrailsApp.run(GrailsApp.groovy:380)
at grails.boot.GrailsApp$run.call(Unknown Source)
at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:47)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:116)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:136)
at com.the41.fraudnet.Application.main(Application.groovy:28) Caused by: java.lang.ClassNotFoundException:
org.springframework.boot.context.embedded.FilterRegistrationBean
at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:335)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
... 34 common frames omitted
FAILURE: Build failed with an exception.
What went wrong: Execution failed for task ':bootRun'.
Process 'command '/opt/jdk1.8.0_131/bin/java'' finished with non-zero exit value 1
I saw in grails 3.3.x upgrade notes:
Spring Boot 1.5.x - supported in grails 3.3.x
Spring Boot 1.5.x removes a number of deprecated classes, notably
several of the classes within the
org.springframework.boot.context.embedded package.
If your application is referencing any of the classes within this
package you will need to alter your imports to use
org.springframework.boot.web.servlet instead.
All classes in the org.springframework.boot.context.web package have
been deprecated and relocated per the Spring Boot 1.4 Release Notes.
And xss-sanitizer plugin is using the classes defined in package "org.springframework.boot.context.embedded"
So, Is there any plans on the upgrade of xss-sanitizer plugin for grails 3.3.x or any workaround for this issue?

There is no reasonable workaround to this other than to upgrade the plugin.
It appears that the plugin is being upgraded; see source here https://github.com/rpalcolea/grails-xss-sanitizer/blob/master/gradle.properties that references grails version 3.3.0. You may also want to track or comment on this issue: https://github.com/rpalcolea/grails-xss-sanitizer/issues/1 since it describes the problem that you are seeing.

ClassNotFoundException: com.allen_sauer.gwt.log.client.WrappedClientThrowable

I'm getting class not found exception for com.allen_sauer.gwt.log.client.WrappedClientThrowable while starting my application in tomcat 8.0.36.
Libraries used
- gwt-user-2.8
- gwt-servlet-2.7.0
- spring4gwt-0.0.1
- gwt-log-3.1.2
This class is present in gwt-log but in package com.allen_sauer.gwt.log.shared. My application code is referring to the correct package but still I'm getting this exception:
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:153)
at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:725)
at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:701)
at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:717)
at org.apache.catalina.startup.HostConfig.deployWAR(HostConfig.java:940)
at org.apache.catalina.startup.HostConfig$DeployWar.run(HostConfig.java:1816)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.NoClassDefFoundError: com/allen_sauer/gwt/log/client/WrappedClientThrowable
at java.lang.Class.getDeclaredMethods0(Native Method)
at java.lang.Class.privateGetDeclaredMethods(Class.java:2701)
at java.lang.Class.getDeclaredMethods(Class.java:1975)
at org.apache.catalina.util.Introspection.getDeclaredMethods(Introspection.java:127)
at org.apache.catalina.startup.WebAnnotationSet.loadMethodsAnnotation(WebAnnotationSet.java:273)
at org.apache.catalina.startup.WebAnnotationSet.loadApplicationServletAnnotations(WebAnnotationSet.java:133)
at org.apache.catalina.startup.WebAnnotationSet.loadApplicationAnnotations(WebAnnotationSet.java:65)
at org.apache.catalina.startup.ContextConfig.applicationAnnotationsConfig(ContextConfig.java:335)
at org.apache.catalina.startup.ContextConfig.configureStart(ContextConfig.java:782)
at org.apache.catalina.startup.ContextConfig.lifecycleEvent(ContextConfig.java:306)
at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:95)
at org.apache.catalina.util.LifecycleBase.fireLifecycleEvent(LifecycleBase.java:90)
at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5202)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:147)
... 10 more
Caused by: java.lang.ClassNotFoundException: com.allen_sauer.gwt.log.client.WrappedClientThrowable
at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1333)
at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1167)
... 24 more
Not sure which library is referring to the old package. Any help is appreciated. Thanks in advance.

Seems like you have a gwt-user and gwt-servlet in different versions.
It would be great if you could post your full "mvn dependency:tree" (or gradle equivalent)
EDIT:
Feels like you are using a somewhat outdated logging library.
https://github.com/fredsa/gwt-log/wiki/GettingStarted
Try adding this guy to your dependencies: compile 'com.allen-sauer.gwt.log:gwt-log:3.3.2

Seems this issue was introduced due to some duplicate compiled classes. I got the application from a different team who have recently converted it to gradle build. When I checked the project structure and gradle scripts, I found many inconsistencies. Basically project was not converted correctly.
After I converted it correctly, this error was gone.
Thanks for the insights, really appreciate it

Spring resource not found - 3.2

We have a project which is using Spring with 3.0 xsd running on tomcat 7. I tried to change the xsd to Spring 3.2 as we have been using spring jars for spring 3.2.4 and 'exclude-mapping' cannot be used with spring 3.0 xsd.
After this change, application stops working, though it does not throw any errors while starting/stopping the server or adding and removing the application.
After the change any request to the application fails with error 404.
Here are the Jars we are using:
beandoc-0.7.0.jar
commons-fileupload-1.2.2.jar
commons-io-1.3.2.jar
commons-logging-1.2-javadoc.jar
commons-logging-1.2.jar
jstl.jar
log4j-1.2.14.jar
ojdbc6.jar
slf4j-api-1.5.6.jar
slf4j-log4j12-1.5.6.jar
spring-beandoc-0.7.1.jar
spring-beans-3.2.4.RELEASE.jar
spring-context-3.2.4.RELEASE.jar
spring-context-support-3.2.4.RELEASE.jar
spring-core-3.2.4.RELEASE.jar
spring-dao-2.0.8.jar
spring-expression-3.2.4.RELEASE.jar
spring-jdbc-3.2.4.RELEASE.jar
spring-web-3.2.4.RELEASE.jar
spring-webmvc-3.2.4.RELEASE.jar
spring-webmvc-portlet-3.2.4.RELEASE.jar
standard.jar
When we try to clean the server, it results in the below exception:
SEVERE: Exception starting Context with name [/COETOOLSACCL]
org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Catalina].StandardHost[localhost].StandardContext[/COETOOLSACCL]]
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:153)
at org.apache.catalina.core.StandardContext.reload(StandardContext.java:4119)
at org.apache.catalina.loader.WebappLoader.backgroundProcess(WebappLoader.java:425)
at org.apache.catalina.core.ContainerBase.backgroundProcess(ContainerBase.java:1341)
at org.apache.catalina.core.ContainerBase$ContainerBackgroundProcessor.processChildren(ContainerBase.java:1542)
at org.apache.catalina.core.ContainerBase$ContainerBackgroundProcessor.processChildren(ContainerBase.java:1552)
at org.apache.catalina.core.ContainerBase$ContainerBackgroundProcessor.processChildren(ContainerBase.java:1552)
at org.apache.catalina.core.ContainerBase$ContainerBackgroundProcessor.run(ContainerBase.java:1520)
at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.NoClassDefFoundError: org/springframework/web/context/support/ServletRequestHandledEvent
at java.lang.Class.getDeclaredFields0(Native Method)
at java.lang.Class.privateGetDeclaredFields(Unknown Source)
at java.lang.Class.getDeclaredFields(Unknown Source)
at org.apache.catalina.util.Introspection.getDeclaredFields(Introspection.java:106)
at org.apache.catalina.startup.WebAnnotationSet.loadFieldsAnnotation(WebAnnotationSet.java:270)
at org.apache.catalina.startup.WebAnnotationSet.loadApplicationServletAnnotations(WebAnnotationSet.java:139)
at org.apache.catalina.startup.WebAnnotationSet.loadApplicationAnnotations(WebAnnotationSet.java:65)
at org.apache.catalina.startup.ContextConfig.applicationAnnotationsConfig(ContextConfig.java:416)
at org.apache.catalina.startup.ContextConfig.configureStart(ContextConfig.java:890)
at org.apache.catalina.startup.ContextConfig.lifecycleEvent(ContextConfig.java:387)
at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:117)
at org.apache.catalina.util.LifecycleBase.fireLifecycleEvent(LifecycleBase.java:90)
at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5503)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:147)
... 8 more
Caused by: java.lang.ClassNotFoundException: org.springframework.web.context.support.ServletRequestHandledEvent
at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1891)
at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1734)
... 22 more
This exception prevails regardless of the xsd versions and with 3.0 application runs normal despite we get this error while cleaning the server.
Please help.

java.lang.RuntimeException: org.apache.nutch.plugin.PluginRuntimeException: java.lang.ClassNotFoundException when parsing with nutch

I'm beginner in Nutch. Tried out some tutorial to crawl the web from NutchWiki. Then I try to make a custom plugin for parsing with the help of this.
All configurations are made and after building using ant my plugin folders are there in build/plugins and runtime/local/plugin and in apache-nutch-1.13-SNAPSHOT.job file. When I parsed the fetched content, I got the following error.
Error parsing: http://example.com/: java.lang.RuntimeException: org.apache.nutch.plugin.PluginRuntimeException: java.lang.ClassNotFoundException: org.apache.nutch.parsefilter.TagExtractorParseFilter
at org.apache.nutch.plugin.PluginRepository.getOrderedPlugins(PluginRepository.java:469)
at org.apache.nutch.parse.HtmlParseFilters.<init>(HtmlParseFilters.java:35)
at org.apache.nutch.parse.html.HtmlParser.setConf(HtmlParser.java:340)
at org.apache.nutch.plugin.Extension.getExtensionInstance(Extension.java:163)
at org.apache.nutch.parse.ParserFactory.getParsers(ParserFactory.java:136)
at org.apache.nutch.parse.ParseUtil.parse(ParseUtil.java:78)
at org.apache.nutch.parse.ParseSegment.map(ParseSegment.java:107)
at org.apache.nutch.parse.ParseSegment.map(ParseSegment.java:45)
at org.apache.hadoop.mapred.MapRunner.run(MapRunner.java:54)
at org.apache.hadoop.mapred.MapTask.runOldMapper(MapTask.java:453)
at org.apache.hadoop.mapred.MapTask.run(MapTask.java:343)
at org.apache.hadoop.mapred.LocalJobRunner$Job$MapTaskRunnable.run(LocalJobRunner.java:243)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)
Caused by: org.apache.nutch.plugin.PluginRuntimeException: java.lang.ClassNotFoundException: org.apache.nutch.parsefilter.TagExtractorParseFilter
at org.apache.nutch.plugin.Extension.getExtensionInstance(Extension.java:167)
at org.apache.nutch.plugin.PluginRepository.getOrderedPlugins(PluginRepository.java:441)
... 16 more
Caused by: java.lang.ClassNotFoundException: org.apache.nutch.parsefilter.TagExtractorParseFilter
at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
at org.apache.nutch.plugin.PluginRepository.getCachedClass(PluginRepository.java:331)
at org.apache.nutch.plugin.Extension.getExtensionInstance(Extension.java:156)
... 17 more
I can't figure what exactly is the problem and I have done all things specified in the tutorial.
Any help will be appreciated.
EDIT : I temporarily solved this issue by hardcoding the classpath of plugin in nutch script file like:
CLASSPATH="${CLASSPATH}:$NUTCH_HOME/plugins/TagExtractorParseFilter/TagExtractorParseFilter.jar"
# distributed mode
EXEC_CALL=(hadoop jar "$NUTCH_JOB")
if $local; then
EXEC_CALL=("$JAVA" $JAVA_HEAP_MAX "${NUTCH_OPTS[#]}" -classpath "$CLASSPATH")
else
.....................

I finally solved this issue. It was due to a small mistake in my plugin.xml.
Earlier the runtime property in plugin.xml was like
<runtime>
<library name="TagExtractorParseFilter">
<export name="*"/>
</library>
</runtime>
I changed it to
<runtime>
<library name="TagExtractorParseFilter.jar">
<export name="*"/>
</library>
</runtime>
Then, it worked.

Jenkins Plugin having trouble using Class?

I'm trying to integrate scribe-java and write a Jenkins Plugin for it, but it seems Jenkins can't be used with Class? Does anyone know why is this?
Jenkins Plugin code:
OAuthService service =
new ServiceBuilder().provider( com.lookout.jenkins.publishoverbox.BoxApi20.class ).apiKey( clientId ).apiSecret(clientSecret ).callback(callbackUrl).grantType( OAuthConstants.AUTHORIZATION_CODE ).build();
Log:
SEVERE: Failed to create Guice container from all the plugins
com.google.common.collect.ComputationException: java.lang.NoClassDefFoundError: Lorg/scribe/oauth/OAuthService;
at com.google.common.collect.ComputingConcurrentHashMap$ComputingMapAdapter.get(ComputingConcurrentHashMap.java:397)
at com.google.inject.internal.FailableCache.get(FailableCache.java:49)
at com.google.inject.internal.MembersInjectorStore.get(MembersInjectorStore.java:66)
at com.google.inject.internal.ConstructorInjectorStore.createConstructor(ConstructorInjectorStore.java:73)
at com.google.inject.internal.ConstructorInjectorStore.access$000(ConstructorInjectorStore.java:29)
at com.google.inject.internal.ConstructorInjectorStore$1.create(ConstructorInjectorStore.java:36)
at com.google.inject.internal.ConstructorInjectorStore$1.create(ConstructorInjectorStore.java:33)
at com.google.inject.internal.FailableCache$1.apply(FailableCache.java:38)
at com.google.common.collect.ComputingConcurrentHashMap$ComputingValueReference.compute(ComputingConcurrentHashMap.java:355)
at com.google.common.collect.ComputingConcurrentHashMap$ComputingSegment.compute(ComputingConcurrentHashMap.java:184)
at com.google.common.collect.ComputingConcurrentHashMap$ComputingSegment.getOrCompute(ComputingConcurrentHashMap.java:153)
at com.google.common.collect.ComputingConcurrentHashMap.getOrCompute(ComputingConcurrentHashMap.java:69)
at com.google.common.collect.ComputingConcurrentHashMap$ComputingMapAdapter.get(ComputingConcurrentHashMap.java:393)
at com.google.inject.internal.FailableCache.get(FailableCache.java:49)
at com.google.inject.internal.ConstructorInjectorStore.get(ConstructorInjectorStore.java:49)
at com.google.inject.internal.ConstructorBindingImpl.initialize(ConstructorBindingImpl.java:127)
at com.google.inject.internal.InjectorImpl.initializeBinding(InjectorImpl.java:506)
at com.google.inject.internal.AbstractBindingProcessor$Processor$1.run(AbstractBindingProcessor.java:171)
at com.google.inject.internal.ProcessedBindingData.initializeBindings(ProcessedBindingData.java:44)
at com.google.inject.internal.InternalInjectorCreator.initializeStatically(InternalInjectorCreator.java:123)
at com.google.inject.internal.InternalInjectorCreator.build(InternalInjectorCreator.java:107)
at com.google.inject.Guice.createInjector(Guice.java:94)
at com.google.inject.Guice.createInjector(Guice.java:71)
at hudson.ExtensionFinder$GuiceFinder.<init>(ExtensionFinder.java:282)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
at java.lang.Class.newInstance0(Class.java:357)
at java.lang.Class.newInstance(Class.java:310)
at net.java.sezpoz.IndexItem.instance(IndexItem.java:181)
at hudson.ExtensionFinder$Sezpoz._find(ExtensionFinder.java:625)
at hudson.ExtensionFinder$Sezpoz.find(ExtensionFinder.java:600)
at hudson.ExtensionFinder._find(ExtensionFinder.java:151)
at hudson.ClassicPluginStrategy.findComponents(ClassicPluginStrategy.java:318)
at hudson.ExtensionList.load(ExtensionList.java:295)
at hudson.ExtensionList.ensureLoaded(ExtensionList.java:248)
at hudson.ExtensionList.iterator(ExtensionList.java:138)
at hudson.ClassicPluginStrategy.findComponents(ClassicPluginStrategy.java:311)
at hudson.ExtensionList.load(ExtensionList.java:295)
at hudson.ExtensionList.ensureLoaded(ExtensionList.java:248)
at hudson.ExtensionList.get(ExtensionList.java:153)
at hudson.PluginManager$PluginUpdateMonitor.getInstance(PluginManager.java:1066)
at hudson.maven.PluginImpl.init(PluginImpl.java:54)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at hudson.init.InitializerFinder.invoke(InitializerFinder.java:120)
at hudson.init.InitializerFinder$TaskImpl.run(InitializerFinder.java:184)
at org.jvnet.hudson.reactor.Reactor.runTask(Reactor.java:259)
at jenkins.model.Jenkins$7.runTask(Jenkins.java:888)
at org.jvnet.hudson.reactor.Reactor$2.run(Reactor.java:187)
at org.jvnet.hudson.reactor.Reactor$Node.run(Reactor.java:94)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:895)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:918)
at java.lang.Thread.run(Thread.java:680)
Caused by: java.lang.NoClassDefFoundError: Lorg/scribe/oauth/OAuthService;
at java.lang.Class.getDeclaredFields0(Native Method)
at java.lang.Class.privateGetDeclaredFields(Class.java:2300)
at java.lang.Class.getDeclaredFields(Class.java:1745)
at com.google.inject.spi.InjectionPoint.getInjectionPoints(InjectionPoint.java:651)
at com.google.inject.spi.InjectionPoint.forInstanceMethodsAndFields(InjectionPoint.java:358)
at com.google.inject.internal.MembersInjectorStore.createWithListeners(MembersInjectorStore.java:91)
at com.google.inject.internal.MembersInjectorStore.access$000(MembersInjectorStore.java:35)
at com.google.inject.internal.MembersInjectorStore$1.create(MembersInjectorStore.java:43)
at com.google.inject.internal.MembersInjectorStore$1.create(MembersInjectorStore.java:40)
at com.google.inject.internal.FailableCache$1.apply(FailableCache.java:38)
at com.google.common.collect.ComputingConcurrentHashMap$ComputingValueReference.compute(ComputingConcurrentHashMap.java:355)
at com.google.common.collect.ComputingConcurrentHashMap$ComputingSegment.compute(ComputingConcurrentHashMap.java:184)
at com.google.common.collect.ComputingConcurrentHashMap$ComputingSegment.getOrCompute(ComputingConcurrentHashMap.java:153)
at com.google.common.collect.ComputingConcurrentHashMap.getOrCompute(ComputingConcurrentHashMap.java:69)
at com.google.common.collect.ComputingConcurrentHashMap$ComputingMapAdapter.get(ComputingConcurrentHashMap.java:393)
... 56 more
Caused by: java.lang.ClassNotFoundException: org.scribe.oauth.OAuthService
at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
... 71 more
Jun 3, 2013 11:37:17 AM jenkins.InitReactorRunner$1 onAttained

What ever you need in your plugin, you specify the same in dependencies.
Reason 1:
Jenkins loads each plugin into a separate class loader to avoid conflicts. Plugins can then participate to the system activities just like other Jenkins built-in classes do. They can participate in XStream-based persistence, they can provide "views" by Jelly, they can provide static resources like images, and from users, everything works seamlessly --- there's no distinction between functionalities that are built-in vs those from plugins.
Reason 2: You don't want to change your code when jenkins change their dependencies.