我将使用rxJava和改造发送获取请求。我这样做的方式是我创建了POST模型和一个名为ApiCall的接口，我还在gradle中添加了以下依赖项：

compile 'com.squareup.retrofit2:retrofit:2.2.0'

compile 'com.android.support:recyclerview-v7:25.3.1'
compile 'com.android.support:design:25.3.1'

compile 'io.reactivex.rxjava2:rxandroid:2.0.1'
compile 'io.reactivex.rxjava2:rxjava:2.0.1'

compile 'com.android.support.constraint:constraint-layout:1.0.2'

compile 'com.squareup.retrofit2:adapter-rxjava:2.0.2'
compile 'com.squareup.retrofit2:converter-gson:2.0.0'

compile 'com.google.code.gson:gson:2.4'

在ApiCall界面中，我这样做：

public interface ApiCall {
    String SERVICE_ENDPOINT = "https://myserverIp";
    @GET("/api/post")
    io.reactivex.Observable<Post> getPost();
}

在我的活动的onResume（）中，我是这样的：

 @Override
    protected void onResume() {
        super.onResume();
        Retrofit retrofit=new Retrofit.Builder()
                .addCallAdapterFactory(RxJavaCallAdapterFactory.create())
                .addConverterFactory(GsonConverterFactory.create())
                .baseUrl("https://198.50.214.15/")
                .build();
        ApiCall apiService=retrofit.create(ApiCall.class);

        Observable<Post> observable=apiService.getPost();

        observable.subscribeOn(Schedulers.newThread())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe(responseData -> {
                    messageList.add(responseData.getTitle());
                    postAdapter.notifyDataSetChanged();
                });

    }

最后我得到这个错误：

Error:Execution failed for task ':app:transformResourcesWithMergeJavaResForDebug'.
> com.android.build.api.transform.TransformException: com.android.builder.packaging.DuplicateFileException: Duplicate files copied in APK META-INF/rxjava.properties
    File1: /home/hussein/.gradle/caches/modules-2/files-2.1/io.reactivex.rxjava2/rxjava/2.0.1/57f850a6b317e5582f1dbaff10a9e7d7e1fcdcfb/rxjava-2.0.1.jar
    File2: /home/hussein/.gradle/caches/modules-2/files-2.1/io.reactivex/rxjava/1.1.1/b494968f6050d494de55dc3ce005e59c7eb40012/rxjava-1.1.1.jar