騰訊面試被懟得體無完膚，Android面試題及答案

A求知若渴 2021-09-18 08:31:33 阅读数:509

android 答案

}


# 簡單使用
本文使用的OkHttp版本為4.7.2。OkHttp的核心類主要有`OkHttpClient`，`Dispatcher`，`Call`，`Request`，`Response`，`Interceptor`，`Chain`。其中`OkHttpClient`是負責管理多個`Call`的組織者，而每個`Call`又包含一個`Request`和`Response`，並且`Call`中的回調用於提供響應結果。要完成一次網絡請求，我們需要告訴`Call`需要處理的`Request`是什麼樣的，例如它的URL是什麼，然後將`Call`交給`OkHttpClient`。`OkHttpClient`僅對本次請求做一些配置，例如指定緩存路徑，它會讓`Dispatcher`去决定何時執行`Call`。而`Dispatcher`的底層實現就是一個由OkHttp默認實現的線程池，它將最終執行`Call`中的`.run()`方法。最後的`Interceptor`和`Chain`將用於數據的攔截處理。OkHttp提供兩種方式提交網絡請求，分別是`Call.execute()`和`Call.enqueue(Callback)`，前者會阻塞線程，後者加入隊列异步執行。通過調用`response.body().string()`我們可以得到響應的body部分並以`String`形式返回，但值得注意的是`.string()`只能調用一次。
* **同步調用**
一般來說要在得到結果的第一時間修改UI，我們可能會使用`Call.execute()`和`AsyncTask`完成提交請求。但`AsyncTask`通常會導致`context`內存泄漏，因為它是非靜態嵌套類，所以不推薦使用同步調用。以下例子使用[https://reqres.in](
)測試請求:


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public class MainActivity extends AppCompatActivity {
private TextView mTextView;
private OkHttpClient mClient = new OkHttpClient();

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mTextView = findViewById(R.id.textView);
String url = "https://reqres.in/api/users/2";
OkHttpHandler okHttpHandler = new OkHttpHandler();
okHttpHandler.execute(url);
}
private class OkHttpHandler extends AsyncTask<String, String, String> {
@Override
protected String doInBackground(String... params) {
Request request = new Request.Builder()
.url(params[0])
.build();
try {
Response response = mClient.newCall(request).execute();
return response.body().string();
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
@Override
protected void onPostExecute(String s) {
super.onPostExecute(s);
mTextView.setText(s);
}
}

}


* **异步調用**
拋開同步調用，使用`Call.enqueue(Callback)`和`Activity.runOnUiThread(Runnable)`的方式是提交請求的最佳方案。其中`Activity.runOnUiThread(Runnable)`方法傳入`Runnable`，這個`Runnable`將插入到UI線程的事件隊列末尾，等待執行`run()`方法。以下例子使用[https://reqres.in](
)測試請求:


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public class MainActivity extends AppCompatActivity {
private TextView mTextView;
private OkHttpClient mClient = new OkHttpClient();

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mTextView = findViewById(R.id.textView);
String url = "https://reqres.in/api/users/2";
try {
get(url);
} catch (IOException e) {
e.printStackTrace();
}
}
private void get(String url) {
Request request = new Request.Builder()
.url(url)
.build();
mClient.newCall(request).enqueue(new Callback() {
@Override
public void onFailure(Call call, IOException e) {
call.cancel();
}
@Override
public void onResponse(Call call, Response response) throws IOException {
final String responseString = response.body().string();
MainActivity.this.runOnUiThread(new Runnable() {
@Override
public void run() {
mTextView.setText(responseString);
}
});
}
});
}

}

HttpUrl.Builder urlBuilder = HttpUrl.parse(“ https://httpbin.org/get”).newBuilder();
urlBuilder.addQueryParameter(“category”, “android”);
urlBuilder.addQueryParameter(“title”, “okhttp”);
String url2 = urlBuilder.build().toString();

Request request = new Request.Builder()
.url(url)
.addHeader(“Accept”,“application/json; charset=utf-8”)
.header(“Accept”,“application/json; charset=utf-8”)
.post(requestBody)
.build();

String headerString=response.header(“Server”);
List<String> headerStrings=response.headers(“Vary”);

Log.i(TAG,headerString);
Iterator<String> it=headerStrings.iterator();
while (it.hasNext()) {
Log.i(TAG,it.next());
}

private static final MediaType JSON = MediaType.parse(“application/json; charset=utf-8”);

String url = “ https://reqres.in/api/users/”;
String jsonString = “{\n” +
" “name”: “morpheus”,\n" +
" “job”: “leader”\n" +
“}”;

private void post(String url, final String requestString) {
RequestBody requestBody = RequestBody.create(JSON, requestString);

Request request = new Request.Builder()
.url(url)
.post(requestBody)
.build();
mClient.newCall(request).enqueue(new Callback() {
@Override
public void onFailure(Call call, IOException e) {
call.cancel();
}
@Override
public void onResponse(Call call, Response response) throws IOException {
final String responseString = response.body().string();
MainActivity.this.runOnUiThread(new Runnable() {
@Override
public void run() {
mTextView.setText(responseString);
}
});
}
});

}

final String url = “ https://tieba.baidu.com/f”;

RequestBody requestBody = new FormBody.Builder()
.add(“ie”, “utf-8”)
.add(“kw”, “minecraft”)
.build();

Request request = new Request.Builder()
.url(url)
.post(requestBody)
.build();

public static final MediaType JPEG = MediaType.parse(“image/jpeg”);

File file = new File(Environment.getExternalStoragePublicDirectory(
Environment.DIRECTORY_DCIM), “building.jpg”);

RequestBody requestBody = RequestBody.create(JPEG, file);

Request request = new Request.Builder()
.url(url)
.post(requestBody)
.build();

RequestBody requestBody = new RequestBody() {
@Nullable
@Override
public MediaType contentType() {
return null;
}

};

Request request = new Request.Builder()
.url(url)
.post(requestBody)
.build();

String url = “ https://api.github.com/gists/c2a7c39532239ff261be”;

class Gist{
Map<String,GistFile> files;
}

class GistFile{
String content;
}

Gson gson = new Gson();
Gist gist = gson.fromJson(response.body().charStream(),Gist.class);
for(Map.Entry<String,GistFile> entry:gist.files.entrySet()){
Log.i(TAG,entry.getKey()+ " "+entry.getValue().content);
}

OkHttpClient client = new OkHttpClient.Builder()
.connectTimeout(3, TimeUnit.SECONDS)
.build();

OkHttpClient client2 = client.newBuilder()
.connectTimeout(5, TimeUnit.SECONDS)
.build();


# 攔截器
攔截器（`Interceptor`）是OkHttp的概念，也是核心功能。OkHttp有兩種攔截器，分別是應用攔截器和網絡攔截器。攔截器的主要目的在於重寫`request`和`response`，可以在發出`request`前修改headers或body，也可以在收到`response`前修改headers或body。我們完全可以在用戶收到`reponse`前將其修改成一個完全不一樣的新`response`，這一功能使得我們可以進行後續的緩存策略修改或是使用gzip壓縮requestBody等操作。應用攔截器在用戶發出一次請求後的全過程中僅調用一次，而網絡攔截器可能因為重定向等問題多次調用，例如有一次重定向就會調用兩次。攔截器可以設置多個，並按添加順序進行攔截。下圖來自[OkHttp文檔](https://links.jianshu.com/go?to=https%3A%2F%2Fsquare.github.io%2Fokhttp%2Finterceptors%2F):
![騰訊面試被懟得體無完膚，Android面試題及答案_移動開發](//upload-images.jianshu.io/upload_images/18068581-afebe969be87b273.png?imageMogr2/auto-orient/strip|imageView2/2/w/1200/format/webp)
兩種攔截器區別如下，參考[OkHttp文檔](https://links.jianshu.com/go?to=https%3A%2F%2Fsquare.github.io%2Fokhttp%2Finterceptors%2F)原文:
> **Application interceptors**
>
> * Don’t need to worry about intermediate responses like redirects and retries.
> * Are always invoked once, even if the HTTP response is served from the cache.
> * Observe the application’s original intent. Unconcerned with OkHttp-injected headers like `If-None-Match`.
> * Permitted to short-circuit and not call `Chain.proceed()`.
> * Permitted to retry and make multiple calls to `Chain.proceed()`.
> * Can adjust `Call` timeouts using `withConnectTimeout`, `withReadTimeout`,`withWriteTimeout`.
>
> **Network Interceptors**
>
> * Able to operate on intermediate responses like redirects and retries.
> * Not invoked for cached responses that short-circuit the network.
> * Observe the data just as it will be transmitted over the network.
> * Access to the `Connection` that carries the request.
個人翻譯如下:
> **應用攔截器**
>
> * 使用時不需要考慮例如重定向、重試等中轉請求帶來的影響
> * 全過程只攔截一次，即使攔截的`response`來自緩存
> * 可處理來自Applcation（參考攔截器圖解）的本意。（例如`no-cache`）不涉及OkHttp的頭部注入例如`If-None-Match`頭部（這是在core注入的）
> * 可以不調用`Chain.proceed()`（例如`return`一個來自緩存的`response`，但不能`return null`）
### 更多Android高級工程師進階學習資料
**進階學習視頻**
![騰訊面試被懟得體無完膚，Android面試題及答案_Android_02](https://s6.51cto.com/images/20210918/1631924540271214.jpg)
附上：我們之前因為秋招收集的二十套一二線互聯網公司Android面試真題（含BAT、小米、華為、美團、滴滴）和我自己整理Android複習筆記（包含Android基礎知識點、Android擴展知識點、Android源碼解析、設計模式匯總、Gradle知識點、常見算法題匯總。）
![騰訊面試被懟得體無完膚，Android面試題及答案_Android_03](https://s7.51cto.com/images/20210918/1631924540320806.jpg)
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版权声明：本文为[A求知若渴]所创，转载请带上原文链接，感谢。 https://gsmany.com/2021/09/20210918083132750P.html

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