The purpose of each jar package under the android system source directory system/framework

1. am.jar: The java library required to execute the am command in the terminal. Source directory: framework/base/cmds/am
2. android.policy.jar: The jar package required for the lock screen interface, this package references android.test.runner.jar, the source directory: framework/base/policy
3. android.test.runner.jar: The jar package required for the test application, which references core.jar, core-junit.ajr and framework.jar, source directory: framework/base/test-runner
4. bmgr.jar: The java library required for the backup and restore operations of all Android Device packages under the adb shell command. Official documentation: http://developer.android.com/guide/developing/tools/bmgr.html . However, this android service is Disabled by default, and the application to be backed up must implement BackupAgent, and add the android:backupAgent attribute to the application tag of AndroidManifest.xml. Source directory: framework/base/cmds/bmgr
5. bouncycastle.jar: java three-party key store, online information said to be used for apk signature, https link and so on, official website: http://www.bouncycastle.org/java.html
6. com.android.future.usb.accessory.jar: The upper-level java library used to manage USB, which will be called by the hardware layer when the system is compiled. Source directory: frameworks/base/libs/usb
7. com.android.location.provider.jar：
8. com.android.nfc_extras.jar: NFC external library. android/nfc/NfcAdapter.java will call NfcAdapterExtras.java in the package. Source directory: frameworks/base/nfc-extras
9. core-junit.jar : The junit core library, called when running *Test.apk.
10. core-junitrunner.jar: unknown, available on the company phone.
11. core-tests*.jar: A series of test jar packages under the framework, which can be deleted when not testing.
12. core.jar: The core library, this is loaded first when starting the desktop. Source directory: 
13. ext.jar: android external three-party expansion package, the source code is mainly external/nist-sip (sip tripartite library under java), external/apache-http (java tripartite library of apache), external/tagsoup (HTML parsing that conforms to the SAX standard) device). In fact, this jar package can add external extension jar packages, just add the src directory to the ext-dir in framework/base/Android.mk.
14. framework-res.apk: android system resource library.
15. framework.jar: The core code in android's sdk.
16. ime.jar: The jar package required by the ime command is used to view the current phone input method list and set the input method. Source directory: framework/base/cmds/ime
17. input.jar: The jar package required by the input command to simulate key input. Source directory: framework/baes/cmds/input
18. javax.obex.jar: java bluetooth API for object exchange protocol. Source directory: framework/base/obex
19. monkey.jar: The jar package required to execute the monkey command. Source directory: framework/base/cmds/monkey
20. pm.jar: The jar package required to execute the pm command. For details of pm, see adb shell pm. Source directory: framework/base/cmds/pm
21. services.jar：话机框架层服务端的编译后jar包，配合libandroid_servers.so在话机启动时通过SystemServer以循环闭合管理的方式将各个service添加到ServiceManager中。源码目录：framework/base/service
22. sqlite-jdbc.jar： sqlite的Java DataBase Connextivity jar包。
23. svc.jar：svc命令所需jar包，可硬用来管理wifi,power和data。源码目录：framework/base/cmds/svc，详情见：http://madgoat.cn/2011/02/android_svc/