遇到一个小问题：
当加入javamail 的三个jar包后遇到报错
java.lang.IllegalArgumentException: already added: Lorg/apache/harmony/awt/internal/nls/Messages;
[2012-08-01 19:08:21 - scoresheetdemo] Dx at com.android.dx.dex.file.ClassDefsSection.add(ClassDefsSection.java:123)
[2012-08-01 19:08:21 - scoresheetdemo] Dx at com.android.dx.dex.file.DexFile.add(DexFile.java:163)
[2012-08-01 19:08:21 - scoresheetdemo] Dx at com.android.dx.command.dexer.Main.processClass(Main.java:486)
[2012-08-01 19:08:21 - scoresheetdemo] Dx at com.android.dx.command.dexer.Main.processFileBytes(Main.java:455)
[2012-08-01 19:08:21 - scoresheetdemo] Dx at com.android.dx.command.dexer.Main.access$400(Main.java:67)
[2012-08-01 19:08:21 - scoresheetdemo] Dx at com.android.dx.command.dexer.Main$1.processFileBytes(Main.java:394)
[2012-08-01 19:08:21 - scoresheetdemo] Dx at com.android.dx.cf.direct.ClassPathOpener.processArchive(ClassPathOpener.java:245)
[2012-08-01 19:08:21 - scoresheetdemo] Dx at com.android.dx.cf.direct.ClassPathOpener.processOne(ClassPathOpener.java:131)
[2012-08-01 19:08:21 - scoresheetdemo] Dx at com.android.dx.cf.direct.ClassPathOpener.process(ClassPathOpener.java:109)
[2012-08-01 19:08:21 - scoresheetdemo] Dx at com.android.dx.command.dexer.Main.processOne(Main.java:418)
[2012-08-01 19:08:21 - scoresheetdemo] Dx at com.android.dx.command.dexer.Main.processAllFiles(Main.java:329)
[2012-08-01 19:08:21 - scoresheetdemo] Dx at com.android.dx.command.dexer.Main.run(Main.java:206)
[2012-08-01 19:08:21 - scoresheetdemo] Dx at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
[2012-08-01 19:08:21 - scoresheetdemo] Dx at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
[2012-08-01 19:08:21 - scoresheetdemo] Dx at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
[2012-08-01 19:08:21 - scoresheetdemo] Dx at java.lang.reflect.Method.invoke(Unknown Source)
[2012-08-01 19:08:21 - scoresheetdemo] Dx at com.android.ide.eclipse.adt.internal.build.DexWrapper.run(DexWrapper.java:179)
[2012-08-01 19:08:21 - scoresheetdemo] Dx at com.android.ide.eclipse.adt.internal.build.BuildHelper.executeDx(BuildHelper.java:745)
[2012-08-01 19:08:21 - scoresheetdemo] Dx at com.android.ide.eclipse.adt.internal.build.builders.PostCompilerBuilder.build(PostCompilerBuilder.java:634)
[2012-08-01 19:08:21 - scoresheetdemo] Dx at org.eclipse.core.internal.events.BuildManager$2.run(BuildManager.java:629)
[2012-08-01 19:08:21 - scoresheetdemo] Dx at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
[2012-08-01 19:08:21 - scoresheetdemo] Dx at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:172)
[2012-08-01 19:08:21 - scoresheetdemo] Dx at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:282)
[2012-08-01 19:08:21 - scoresheetdemo] Dx at org.eclipse.core.internal.events.BuildManager.build(BuildManager.java:363)
[2012-08-01 19:08:21 - scoresheetdemo] Dx at org.eclipse.core.internal.resources.Project$1.run(Project.java:545)
[2012-08-01 19:08:21 - scoresheetdemo] Dx at org.eclipse.core.internal.resources.Workspace.run(Workspace.java:1975)
[2012-08-01 19:08:21 - scoresheetdemo] Dx at org.eclipse.core.internal.resources.Project.internalBuild(Project.java:524)
[2012-08-01 19:08:21 - scoresheetdemo] Dx at org.eclipse.core.internal.resources.Project.build(Project.java:123)
[2012-08-01 19:08:21 - scoresheetdemo] Dx at com.android.ide.eclipse.adt.internal.project.ProjectHelper.doFullIncrementalDebugBuild(ProjectHelper.java:961)
[2012-08-01 19:08:21 - scoresheetdemo] Dx at com.android.ide.eclipse.adt.internal.launch.LaunchConfigDelegate.launch(LaunchConfigDelegate.java:146)
[2012-08-01 19:08:21 - scoresheetdemo] Dx at org.eclipse.debug.internal.core.LaunchConfiguration.launch(LaunchConfiguration.java:853)
[2012-08-01 19:08:21 - scoresheetdemo] Dx at org.eclipse.debug.internal.core.LaunchConfiguration.launch(LaunchConfiguration.java:702)
[2012-08-01 19:08:21 - scoresheetdemo] Dx at org.eclipse.debug.internal.ui.DebugUIPlugin.buildAndLaunch(DebugUIPlugin.java:924)
[2012-08-01 19:08:21 - scoresheetdemo] Dx at org.eclipse.debug.internal.ui.DebugUIPlugin$8.run(DebugUIPlugin.java:1128)
[2012-08-01 19:08:21 - scoresheetdemo] Dx at org.eclipse.core.internal.jobs.Worker.run(Worker.java:54)
[2012-08-01 19:08:23 - scoresheetdemo] Dx 1 error; aborting
[2012-08-01 19:08:23 - scoresheetdemo] Conversion to Dalvik format failed with error 1
找了很多方法比如重新导入jar包之类，但是都没用。最后回到错误本身，发现当我只用其中任意一个external包的时候都不会出错，是两个包有相同的类，打开看都是一样的，于是我删掉其中一个就好了。