1 page.title=Zipalign: an Easy Optimization 2 @jd:body 3 4 <p>The Android SDK includes a tool called <a 5 href="{@docRoot}guide/developing/tools/zipalign.html"><code>zipalign</code></a> 6 that optimizes the way an application is packaged. Running zipalign against your 7 application enables Android to interact it more efficiently at run time and thus 8 has the potential to make it and the overall system run faster. We strongly 9 encourage you to use <code>zipalign</code> on both new and already published 10 applications and to make the optimized version available — even if your 11 application targets a previous version of Android. This article describes how 12 <code>zipalign</code> helps performance and how to use it to optimize your 13 app.</p> 14 15 <p>In Android, data files stored in each application's apk are accessed by 16 multiple processes: the installer reads the manifest to handle the 17 permissions associated with that application; the Home application 18 reads resources to get the application's name and icon; the system 19 server reads resources for a variety of reasons (e.g. to display that 20 application's notifications); and last but not least, the resource 21 files are obviously used by the application itself.</p> 22 23 <p>The resource-handling code in Android can efficiently access resources when 24 they're aligned on 4-byte boundaries by memory-mapping them. But for resources 25 that are not aligned (that is, when <code>zipalign</code> hasn't been run on an 26 apk), it has to fall back to explicitly reading them — which is slower and 27 consumes additional memory.</p> 28 29 <p>For an application developer, this fallback mechanism is very 30 convenient. It provides a lot of flexibility by allowing for several 31 different development methods, including those that don't include 32 aligning resources as part of their normal flow.</p> 33 34 <p>Unfortunately, for users the situation is reversed — reading resources 35 from unaligned apks is slow and takes a lot of memory. In the best case, the 36 only visible result is that both the Home application and the unaligned 37 application launch slower than they otherwise should. In the worst case, 38 installing several applications with unaligned resources increases memory 39 pressure, thus causing the system to thrash around by having to constantly start 40 and kill processes. The user ends up with a slow device with a poor battery 41 life.</p> 42 43 <p>Luckily, it's very easy for you to align the resources in your application:</p> 44 45 <ul> 46 <li>Using ADT:</li> 47 <li style="list-style-type: none; list-style-image: none; list-style-position: outside;"> 48 <ul> 49 <li>The ADT plugin for Eclipse (starting from version 0.9.3) will automatically 50 align release application packages if the export wizard is used to create them. 51 To use the wizard, right click the project and choose "Android Tools" > 52 "Export Signed Application Package..." It can also be accessed from the first 53 page of the <code>AndroidManifest.xml</code> editor.</li> 54 </ul> 55 </li> 56 <li>Using Ant:</li><li style="list-style-type: none; list-style-image: none; list-style-position: outside;"> 57 58 <ul> 59 <li>The <em>Ant</em> build script (starting from Android 1.6) can align 60 application packages. Targets for older versions of the Android platform are not 61 aligned by the <em>Ant</em> build script and need to be manually aligned.</li> 62 <li>Starting from the Android 1.6 SDK, Ant aligns and signs packages automatically, 63 when building in debug mode.</li> 64 <li>In release mode, Ant aligns packages only if it has enough 65 information to sign the packages, since aligning has to happen after signing. In 66 order to be able to sign packages, and therefore to align them, <em>Ant</em> 67 needs to know the location of the keystore and the name of the key in 68 <code>build.properties</code>. The name of the properties are 69 <code>key.store</code> and <code>key.alias</code> respectively. If those 70 properties are present, the signing tool will prompt to enter the store/key 71 passwords during the build, and the script will sign and then align the apk 72 file. If the properties are missing, the release package will not be signed, and 73 therefore will not get aligned either.</li> 74 </ul> 75 </li> 76 <li>Manually:</li> 77 <li style="list-style-type: none; list-style-image: none; list-style-position: outside;"> 78 <ul> 79 <li>In order to manually align a package, <code>zipalign</code> 80 is in the <code>tools/</code> folder of Android 1.6 and later SDKs. You can use 81 it to align application packages targeting any version of Android. You should run 82 it only after signing the apk file, using the following command: 83 <br><code>zipalign -v 4 source.apk destination.apk</code></li> 84 </ul> 85 </li> 86 <li>Verifying alignment:</li> 87 <li style="list-style-type: none; list-style-image: none; list-style-position: outside;"> 88 <ul> 89 <li>The following command verifies that a package is aligned:<br><code>zipalign -c -v 4 application.apk</code> 90 </li> 91 </ul> 92 </li> 93 </ul> 94 95 <p>We encourage you manually run <code>zipalign</code> 96 on your currently published applications and to make the newly aligned 97 versions available to users. Also, don't forget to align any new 98 applications going forward!</p> 99
