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本文主要介绍了Android studio利用gradle打jar包并混淆的方法，下面话不多说，来看看详细的介绍吧。
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首先打jar包的配置很简单，使用jar的task，可以参考gradle官方文档，具体代码如下：
task buildJar(type: Jar, dependsOn: ['assembleRelease']) {
destinationDir = file('build/outputs/jar/')
appendix = ""
baseName = ""
version = SDK_VERSION
// manifest信息
def map = ['Version': SDK_VERSION,
'Gradle': project.gradle.gradleVersion,
'Vendor': '',
'Date': new Date().getDateTimeString()
]
manifest.attributes(map)
from('build/intermediates/classes/release/')
exclude('**/BuildConfig.class')
exclude('**/BuildConfig\$*.class')
exclude('**/R.class')
exclude('**/R\$*.class')
include('**/*.class')
}但是发现上面打出来的jar包中的代码没有被混淆，于是加混淆。使用混淆的proguard.gradle.ProGuardTask task时，发现总是报如下错误：
java.io.IOException: The output jar [....jar] must be specified after an input jar, or it will be empty.
按照上面的提示，outjars是写在injars后面啊，it will be empty是提示哪里有问题？以为是proguard-rules.pro文件中的配置有问题，结果把文件清空，还是报上面的错误，错误原因不得而知了。在这个问题上耗了很长时间，最终还是没有解决。
突然看到上面的assembleRelease task想起了平常打APK时，会使用到这个task，打出来的APK会自动混淆。
那这个assembleRelease task就会依赖处理混淆的task，于是查看了输出日志：
To honour the JVM settings for this build a new JVM will be forked. Please consider using the daemon: https://docs.gradle.org/2.14.1/userguide/gradle_daemon.html. Observed package id 'system-images;android-22;google_apis;x86' in inconsistent location 'android-sdk-windows-studio\system-images\addon-google_apis-google-22 \x86' (Expected 'android-sdk-windows-studio\system-images\android-22\google_apis\x86') Observed package id 'system-images;android-22;google_apis;x86' in inconsistent location 'android-sdk-windows-studio\system-images\addon-google_apis-google-22 \x86' (Expected 'android-sdk-windows-studio\system-images\android-22\google_apis\x86') Incremental java compilation is an incubating feature. :sdk:preBuild UP-TO-DATE :sdk:extractProguardFiles :sdk:preReleaseBuild :sdk:checkReleaseManifest :sdk:preDebugAndroidTestBuild UP-TO-DATE :sdk:preDebugBuild UP-TO-DATE :sdk:preDebugUnitTestBuild UP-TO-DATE :sdk:preReleaseUnitTestBuild UP-TO-DATE :sdk:prepareComAndroidSupportAnimatedVectorDrawable2510Library UP-TO-DATE :sdk:prepareComAndroidSupportAppcompatV72510Library UP-TO-DATE :sdk:prepareComAndroidSupportSupportCompat2510Library UP-TO-DATE :sdk:prepareComAndroidSupportSupportCoreUi2510Library UP-TO-DATE :sdk:prepareComAndroidSupportSupportCoreUtils2510Library UP-TO-DATE :sdk:prepareComAndroidSupportSupportFragment2510Library UP-TO-DATE :sdk:prepareComAndroidSupportSupportMediaCompat2510Library UP-TO-DATE :sdk:prepareComAndroidSupportSupportV42510Library UP-TO-DATE :sdk:prepareComAndroidSupportSupportVectorDrawable2510Library UP-TO-DATE :sdk:prepareReleaseDependencies :sdk:compileReleaseAidl UP-TO-DATE :sdk:compileReleaseNdk UP-TO-DATE :sdk:compileLint UP-TO-DATE :sdk:copyReleaseLint UP-TO-DATE :sdk:compileReleaseRenderscript UP-TO-DATE :sdk:generateReleaseBuildConfig :sdk:generateReleaseResValues UP-TO-DATE :sdk:generateReleaseResources UP-TO-DATE :sdk:mergeReleaseResources UP-TO-DATE :sdk:processReleaseManifest UP-TO-DATE :sdk:processReleaseResources UP-TO-DATE :sdk:generateReleaseSources :sdk:incrementalReleaseJavaCompilationSafeguard :sdk:compileReleaseJavaWithJavac :sdk:compileReleaseJavaWithJavac - is not incremental (e.g. outputs have changed, no previous execution, etc.). 注: 某些输入文件使用或覆盖了已过时的 API。 注: 有关详细信息, 请使用 -Xlint:deprecation 重新编译。 :sdk:extractReleaseAnnotations :sdk:mergeReleaseShaders UP-TO-DATE :sdk:compileReleaseShaders UP-TO-DATE :sdk:generateReleaseAssets UP-TO-DATE :sdk:mergeReleaseAssets UP-TO-DATE :sdk:mergeReleaseProguardFiles UP-TO-DATE :sdk:packageReleaseRenderscript UP-TO-DATE :sdk:packageReleaseResources UP-TO-DATE :sdk:processReleaseJavaRes UP-TO-DATE :sdk:transformResourcesWithMergeJavaResForRelease UP-TO-DATE :sdk:transformClassesAndResourcesWithProguardForRelease ProGuard, version 5.2.1 Reading input... Reading program directory [sdk\build\intermediates\classes\release] (filtered) Reading library jar [sdk\build\intermediates\exploded-aar\com.android.support\support-media-compat\25.1.0\jars\classes.jar] (filtered) Reading library jar [sdk\build\intermediates\exploded-aar\com.android.support\support-compat\25.1.0\jars\classes.jar] (filtered) Reading library jar [sdk\build\intermediates\exploded-aar\com.android.support\support-fragment\25.1.0\jars\classes.jar] (filtered) Reading library jar [sdk\build\intermediates\exploded-aar\com.android.support\support-core-ui\25.1.0\jars\classes.jar] (filtered) Reading library jar [sdk\build\intermediates\exploded-aar\com.android.support\animated-vector-drawable\25.1.0\jars\classes.jar] (filte red) Reading library jar [android-sdk-windows-studio\extras\android\m2repository\com\android\support\support-annotations\25.1.0\support-annotations-25.1.0.jar] (f iltered) Reading library jar [sdk\build\intermediates\exploded-aar\com.android.support\support-v4\25.1.0\jars\classes.jar] (filtered) Reading library jar [sdk\build\intermediates\exploded-aar\com.android.support\support-vector-drawable\25.1.0\jars\classes.jar] (filter ed) Reading library jar [sdk\build\intermediates\exploded-aar\com.android.support\appcompat-v7\25.1.0\jars\classes.jar] (filtered) Reading library jar [sdk\build\intermediates\exploded-aar\com.android.support\support-core-utils\25.1.0\jars\classes.jar] (filtered) Reading library jar [\android-sdk-windows-studio\platforms\android-25\android.jar] Reading library jar [\android-sdk-windows-studio\platforms\android-25\optional\org.apache.http.legacy.jar] Note: duplicate definition of library class [android.net.http.HttpResponseCache] Note: duplicate definition of library class [android.net.http.SslCertificate$DName] Note: duplicate definition of library class [android.net.http.SslError] Note: duplicate definition of library class [android.net.http.SslCertificate] Note: duplicate definition of library class [org.apache.http.params.CoreConnectionPNames] Note: duplicate definition of library class [org.apache.http.params.HttpConnectionParams] Note: duplicate definition of library class [org.apache.http.params.HttpParams] Note: duplicate definition of library class [org.apache.http.conn.scheme.SocketFactory] Note: duplicate definition of library class [org.apache.http.conn.scheme.LayeredSocketFactory] Note: duplicate definition of library class [org.apache.http.conn.scheme.HostNameResolver] Note: duplicate definition of library class [org.apache.http.conn.ConnectTimeoutException] Note: there were 11 duplicate class definitions. (http://proguard.sourceforge.net/manual/troubleshooting.html#duplicateclass) Initializing... Note: you're ignoring all warnings! Ignoring unused library classes... Original number of library classes: 5857 Final number of library classes: 383 Printing kept classes, fields, and methods... Shrinking... Printing usage to [sdk\build\outputs\mapping\release\usage.txt]... Removing unused program classes and class elements... Original number of program classes: 52 Final number of program classes: 48 Obfuscating... Printing mapping to [sdk\build\outputs\mapping\release\mapping.txt]... Writing output... Preparing output jar [sdk\build\intermediates\transforms\proguard\release\jars\3\3\main.jar] Copying resources from program directory [sdk\build\intermediates\classes\release] (filtered) Printing classes to [sdk\build\outputs\mapping\release\dump.txt]... :sdk:transformClassesAndResourcesWithSyncLibJarsForRelease :sdk:mergeReleaseJniLibFolders UP-TO-DATE :sdk:transformNative_libsWithMergeJniLibsForRelease UP-TO-DATE :sdk:transformNative_libsWithSyncJniLibsForRelease UP-TO-DATE :sdk:bundleRelease :sdk:compileReleaseSources :sdk:assembleRelease :sdk:buildJar BUILD SUCCESSFUL.
好家伙，被我发现了。其中从:sdk:transformClassesAndResourcesWithProguardForRelease这个task就可以看到，下面一堆日志是关于ProGuard混淆工具的，最后可以看到：
Preparing output jar [sdk\build\intermediates\transforms\proguard\release\jars\3\3\main.jar]
这个main.jar就是混淆后的jar包，只不过这个jar还包含了R类和BuildConfig类的信息，所以将这个信息过滤掉就可以。但问题也来了，jar包都已经打好了，怎么配置混淆？解决方法是只要把jar包当输入就行了，最终配置如下：
task buildJar(type: Jar, dependsOn: ['assembleRelease']) {
destinationDir = file('build/outputs/jar/')
appendix = "" // SDK的后缀名称
baseName = "" // SDK名称
version = SDK_VERSION // 这个常量是在gradle.properties中配置的
// manifest信息
def map = ['Version': SDK_VERSION,
'Gradle': project.gradle.gradleVersion,
'Vendor': '',
'Date': new Date().getDateTimeString()
]
manifest.attributes(map)
from(project.zipTree('build/intermediates/transforms/proguard/release/jars/3/3/main.jar'))
exclude('**/BuildConfig.class')
exclude('**/BuildConfig\$*.class')
exclude('**/R.class')
exclude('**/R\$*.class')
include('**/*.class')
}总结
OK，任务搞定。以上就是这篇文章的全部内容了，希望本文的内容对各位Android开发者们能带来一定的帮助，如果有疑问大家可以留言交流，谢谢大家对创新互联的支持。
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