【Android】Android Studio 进行代码混淆，打包release APK

apply plugin: ‘com.android.application‘

android {
    compileSdkVersion 19
    buildToolsVersion ‘23.0.1‘

    defaultConfig {
        applicationId "com.rayclear.juchang"
        minSdkVersion 17
        targetSdkVersion 23
        versionCode 4
        versionName "1.03"
    }
    buildTypes {
        release {
            //代码混淆开关，一定要注意现在已经使用minifyEnabled代替runProguard了
            minifyEnabled true
            // proguard-rules.pro 是当前使用的混淆文件（Eclipse中的proguard.cfg)
            proguardFiles getDefaultProguardFile(‘proguard-android.txt‘), ‘proguard-rules.pro‘
        }
    }

    packagingOptions {
        exclude ‘META-INF/DEPENDENCIES‘
        exclude ‘META-INF/LICENSE‘
        exclude ‘META-INF/LICENSE.txt‘
        exclude ‘META-INF/license.txt‘
        exclude ‘META-INF/NOTICE‘
        exclude ‘META-INF/NOTICE.txt‘
        exclude ‘META-INF/notice.txt‘
        exclude ‘META-INF/ASL2.0‘
    }

    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_7
        targetCompatibility JavaVersion.VERSION_1_7
    }
}

1.一直处于Gradle Build Running...
被坑了两次，一直以为是真的在打包，IDE也木有个具体提示什么的，就干等了好久。
遇到这种情况，直接关掉Android Studio重新开始吧。正常来说一个普通的APP打包混淆时长也就是1～3分钟吧。

2.关于cache.properties.lock的错：
Error:Timeout waiting to lock cp_proj class cache for build file ‘/Users/raomengyang/work/app/build.gradle‘ (/Users/raomengyang/.gradle/caches/2.8/scripts/build_aldsk0ke4ednnd4pf0nybqlhq/cp_proj). It is currently in use by another Gradle instance.
Owner PID: unknown
Our PID: 20080
Owner Operation: unknown
Our operation: Initialize cache
Lock file: /Users/raomengyang/.gradle/caches/2.8/scripts/build_aldsk0ke4ednnd4pf0nybqlhq/cp_proj/cache.properties.lock
之前遇到过同样的情况，是将带lock的文件给恢复权限解决的，可是这次不管用，于是退出AS重新来，每次遇到这个问题然后退出AS都会提示后台还有任务没有结束，所以这个错误个人感觉是AS还有后台任务没有被结束，以至于一直hold在这儿。

3.各种specified twice：
java.io.IOException: The same input jar [/Users/raomengyang/work/app/libs/**] is specified twice.
删掉proguard文件中的重复声明引用的jar文件。

4.满天的Warning：
Note: there were 157 duplicate class definitions.
      (http://proguard.sourceforge.net/manual/troubleshooting.html#duplicateclass)
Warning:library class org.apache.http.auth.AuthenticationException extends or implements program class org.apache.http.ProtocolException
Warning:library class org.apache.http.auth.MalformedChallengeException extends or implements program class org.apache.http.ProtocolException
Warning:library class org.apache.http.auth.params.AuthParamBean extends or implements program class org.apache.http.params.HttpAbstractParamBean
Warning:library class org.apache.http.client.NonRepeatableRequestException extends or implements program class org.apache.http.ProtocolException
Warning:library class org.apache.http.client.RedirectException extends or implements program class org.apache.http.ProtocolException
Warning:library class org.apache.http.client.entity.UrlEncodedFormEntity extends or implements program class org.apache.http.entity.StringEntity
Warning:library class org.apache.http.client.methods.HttpEntityEnclosingRequestBase extends or implements program class org.apache.http.HttpEntityEnclosingRequest
Warning:library class org.apache.http.client.methods.HttpRequestBase extends or implements program class org.apache.http.message.AbstractHttpMessage
Warning:library class org.apache.http.client.methods.HttpUriRequest extends or implements program class org.apache.http.HttpRequest
Warning:library class org.apache.http.client.params.AllClientPNames extends or implements program class org.apache.http.params.CoreConnectionPNames
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Warning:library class org.apache.http.client.params.AllClientPNames extends or implements program class org.apache.http.params.CoreProtocolPNames
Warning:library class org.apache.http.client.params.ClientParamBean extends or implements program class org.apache.http.params.HttpAbstractParamBean
Warning:library class org.apache.http.client.protocol.RequestAddCookies extends or implements program class org.apache.http.HttpRequestInterceptor
Warning:library class org.apache.http.client.protocol.RequestDefaultHeaders extends or implements program class org.apache.http.HttpRequestInterceptor
Warning:library class org.apache.http.client.protocol.RequestProxyAuthentication extends or implements program class org.apache.http.HttpRequestInterceptor

该类问题都可以根据我们的class文件来进行以下声明：
例如：现在提示的是org.apache.http.* 这个包里的类有问题，那么就加入下述代码：
-keep class org.apache.http.** { *; }
-dontwarn org.apache.http.**
依此类推，注意一点，混淆完后，就算打包成功也需要再次测试，因为APP内部可能会出现上述问题。