Android 6.0版本已經已經基本將Apahce Http Client 移除出SDK，會報出以下錯誤：

" Unable to find optional library: org.apache.http.legacy"

 那麼問題來了，如果我在以前的專案中使用了Apache HttpClient相關類，怎麼辦呢？

請看官網給出的解決

Apache HTTP Client Removal

Android 6.0 release removes support for the Apache HTTP client. If your app is using this client and targets Android 2.3 (API level 9) or higher, use the  class instead. This API is more efficient because it reduces network use through transparent compression and response caching, and minimizes power consumption. To continue using the Apache HTTP APIs, you must first declare the following compile-time dependency in your build.gradle

android {
    useLibrary 'org.apache.http.legacy'}

解決辦法：

     1、看看目錄D:\Android\sdk\platforms\android-23\optional 下有沒有org.apache.http.legacy.jar 和 optional.json

     2、如果沒有optional.json，則自己新建一個這樣的檔案，然後加入如下內容:

1. [  
2.   {  
3.     "name": "org.apache.http.legacy",  
4.     "jar": "org.apache.http.legacy.jar",  
5.     "manifest": false  
6.   }  
7. ]