Android 编程下通过 zipalign 对 APK 文件进行优化

zipalign

zipalign is an archive alignment tool that provides important optimization to Android application (.apk) files. The purpose is to ensure that all uncompressed data starts with a particular alignment relative to the start of the file. Specifically, it causes all uncompressed data within the .apk, such as images or raw files, to be aligned on 4-byte boundaries. This allows all portions to be accessed directly with mmap() even if they contain binary data with alignment restrictions. The benefit is a reduction in the amount of RAM consumed when running the application.

This tool should always be used to align your .apk file before distributing it to end-users. The Android build tools can handle this for you. When using Eclipse with the ADT plugin, the Export Wizard will automatically zipalign your .apk after it signs it with your private key. The build scripts used when compiling your application with Ant will also zipalign your .apk, as long as you have provided the path to your keystore and the key alias in your project ant.properties file, so that the build tools can sign the package first.

Caution: zipalign must only be performed after the .apk file has been signed with your private key. If you perform zipalign before signing, then the signing procedure will undo the alignment. Also, do not make alterations to the aligned package. Alterations to the archive, such as renaming or deleting entries, will potentially disrupt the alignment of the modified entry and all later entries. And any files added to an "aligned" archive will not be aligned.

The adjustment is made by altering the size of the "extra" field in the zip Local File Header sections. Existing data in the "extra" fields may be altered by this process.

For more information about how to use zipalign when building your application, please read Signing Your Applications.

Usage

To align infile.apk and save it as outfile.apk:

zipalign [-f] [-v] <alignment> infile.apk outfile.apk

To confirm the alignment of existing.apk:

zipalign -c -v <alignment> existing.apk

The <alignment> is an integer that defines the byte-alignment boundaries. This must always be 4 (which provides 32-bit alignment) or else it effectively does nothing.

Flags:

• -f : overwrite existing outfile.zip
• -v : verbose output
• -c : confirm the alignment of the given file

以上对 zipalign 的介绍和使用来自 Google Developer，下面开始实例演示：

1. 将 Android-SDK\tools 目录下的 zipalign.exe 文件拷贝到放置签名APK文件所在的目录（fileDir）
2. 调用 cmd 窗口，在窗口中执行 cd /d fileDir，进入签名APK文件所在的目录
3. 继续在 cmd 窗口中执行 zipalign -v 4 inFile.apk outFile.apk，看到窗口输出 Verification succesful 即完成了 APK 的优化（inFile.apk 为已经签名打包好的原始文件，outFile.apk 为优化完毕后的输出文件）