Apk packaging process

Typical Android The construction process of application modules usually follows the following steps ：

• Compiler converts source code into .DEX（Dalvik Executable） file （ These include Android Bytecode running on the device ）, Convert all other content into compiled resources ;
• APK The packer will .DEX Combine files and compiled resources into a single file APK. however , You must sign APK, To install and deploy the application to Android On the device ;
• APK Packers use debugging or publishing keystores to sign APK;
  • If you build a debug version of the application （ That is, applications designed for testing and Analysis ）, The packer will use the debug keystore to sign the application . Android Studio Automatically configure new projects using the debug keystore ;
  • If you build a release version application that you plan to release , The packer will use the publishing keystore to sign the application ;
• At the end of the generation APK Before , The packer will use zipalign Tools to optimize applications , Reduce the memory used when running on the device ;

1 Package resource files

stay Android During the compilation of the application ,AAPT(Android Assert Packaging Tool) The tool will be right res Compile the resource files under the directory , Generate a resource.arsc file ,resource.arsc A file is equivalent to a file index table , It records a lot of information related to resources . Each such file will be assigned a resource id, Access to such resources , The application layer code is through resource id visiting .

take .apk After decompressing （apk The essence is a .zip Compressed package ） You'll see it resources.arsc, It's actually APP Resource files for . Simply speaking , adopt resources.arsc You can locate the memory address of the resource .

2 Handle aidl files

If there is .aidl file , Will pass aidl Tools （ The source code is located in system/tools/aidl）, Pack it up .java Interface class .aidl The tool parses the interface definition file and generates the corresponding Java Code interface for program call . If not used in the project aidl file , You can skip this step .

AIDL(Android Interface Definition Language), yes Android Interface definition language . The purpose is to facilitate inter process communication , Especially in the case of multi process concurrency . Its essence is to Binder Encapsulation of communication .

3 compile （Compilers）

Engineering source （ All of the Java Code ）+ R.java + aidl.java adopt javac Generate .class file .

4 Generate .dex file

.class Documents and third parties jar perhaps library adopt dx The tools are packed into .dex file .

5 apkbuilder（ Generate unsigned apk）

apkbuilder The tool will save all resources that have not been compiled 、.arsc resources 、.dex Package the files into a complete apk In file .

6 Jarsigner（ Signature ）

jarsigner The tool will respond to unsigned apk Verify the signature , After getting a signature apk——signed.apk. once APK File generation , It has to be signed to be installed on the device .

7 zipalign（ alignment ）

zipAlign Tool pair signed.apk Do alignment . If the APK If it's the official version , You have to be right APK Do alignment , The tools used are zipalign（[ Catalog ]\Android\sdk\build-tools\[ Version number ]\zipalign.exe） . The so-called alignment , The main process is to APK All resource files in the package are offset from the beginning of the file by 4 Integer multiples of bytes , This is accessed through memory mapping apk Files will be faster .

Reference resources

APK Packaging process