1. brief introduction

in the past ,Android Send on HTTP There are generally two ways to request ：HttpURLConnection and HttpClient（Apache HttpClient）. But due to the HttpClient There is API Too many 、 It's difficult to expand ,Android The team is increasingly not suggesting that we use this approach . Finally in the Android 6.0 In the system ,HttpClient Has been completely removed , It indicates that this function has been officially abandoned . Although the official recommendation is HttpURLConnection, But in the process of code writing, it will still be more cumbersome . here , A network layer framework to replace them has emerged ： That is to say Okhttp, The framework is also where I am 《Android First line of code 》 What you learn is nothing more than Litepal The second frame after that . Today, I have learned again Okhttp, Record the learning process on a blog , I hope it will help the readers .
OkHttp It's by the great name Square company-developed , This company has contributed a lot to the cause of open source , except OkHttp outside , And developed something like Picasso,Retrofit And other famous open source projects .OkHttp Not only is it easy to do on interface encapsulation , Even in the underlying implementation, it's a school of its own , Compared with the original HttpURLConnection, It can be said that there are too many , Now it has become a vast Android Developer's preferred network communication library .

2. characteristic

OkHttp It's an efficient HTTP client , It has the following default features ：

• Support HTTP/2, Allow all requests with the same host address to share the same socket Connect
• Connection pooling reduces request latency
• Transparent GZIP Compression reduces the size of response data
• Cache response content , Avoid completely repeated requests

When there's a problem with the Internet OkHttp Still stick to your duty , It will automatically recover general connection problems , If you have more than one service IP Address , When the first one IP When the request fails ,OkHttp Will alternate between trying your configuration of other IP,OkHttp Use modern TLS technology (SNI, ALPN) Initializing a new connection , When the handshake fails, it will go back to TLS 1.0.

OkHttp Support Android 2.3 And above Android platform , as well as Java,JDK 1.7 And above .

OkHttp The use of is very simple . Its request / Respond to API Use Constructor mode builders To design , It supports blocking Synchronization request And with callback Asynchronous requests .
In order to better demonstrate OkHttp, Only synchronization is shown here / Asynchronous execution get/post The relevance of the request api, As for OkHttp Related calls to , Suggestions for reference OkHttp Official documents of ：OkHttp Official website , No need to turn over the wall
About use post Request to send flow / file / Forms etc. , These functions need to be combined with another framework ：OkIo, It will be shown in the next blog .
Don't talk much , Let's start using OkHttp Well .

3. demonstration

3.1 Integrate

It's the integration link that we love , We just need to modify it module Under the build.gradle, Join in OkHttp Dependence , The code is as follows ：

implementation("com.squareup.okhttp3:okhttp:4.6.0")

Remember again Sync once , Make sure OkHttp Integrated into your project . When the author wrote this blog OkHttp3 Stable version number to achieve 4.6.0, If the reader is in OkHttp An updated version of , Remember to update in time , Keep pace with the times .

3.2 To configure

Now that you've integrated OkHttp, It is necessary to carry out network related operations . In that case , You need to declare the network permissions under the manifest file , namely ：

<uses-permission android:name="android.permission.INTERNET" />

in addition ： If your Android Version is Android P（ namely targetSdkVersion 27）, Errors about the network may be reported when running the project , As shown in the figure ：

reason ： stay Android P On the equipment of the system , If the application uses unencrypted plaintext traffic http Network request , This will cause the application to be unable to make network requests ,https Will not be affected , In the same way, if the application uses WebView Load web page Then loading the web page also needs to be https request .
resolvent ：

• APP The overall network request is changed to https
• take targetSdkVersion Version down to 27 following
• Change project network security configuration

Three methods are also available , Here is the third solution , To broaden the solution

1. stay res New under the directory xml Folder stay xml The new name in the folder is network_config( The name is not fixed ) Of xml, The code is as follows ：

<network-security-config>
<base-config cleartextTrafficPermitted="true" />
</network-security-config>

2. then , stay AndroidManifest add android:networkSecurityConfig attribute , The code is as follows ：

 <application
...
android:networkSecurityConfig="@xml/network_security_config"
...
/>

3. The above two steps complete the network security configuration , If you can't, you can try another two methods or Baidu

3.3 Layout files and URL encapsulation

Next , Let's go straight to layout the document activity_main.xml Compiling . The layout is simple , There are only four buttons , The code is as follows ：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity"
android:orientation="vertical">
<Button
android:id="@+id/btn_get_syn"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text=" send out get request —— Sync "/>
<Button
android:id="@+id/btn_get_asy"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text=" send out get request —— asynchronous "/>
<Button
android:id="@+id/btn_post_syn"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text=" send out post request —— asynchronous "/>
<Button
android:id="@+id/btn_post_asy"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text=" send out post request —— asynchronous "/>
</LinearLayout>

after , Let's simply encapsulate the requested URL, namely http://wwww.baidu.com. It is suggested that you want to go deep OkHttp Of the readers themselves build a Tomcat/Apache The server , Upload the resource file to the server , Then visit the local path , This can deepen the understanding of network requests . Here in order to facilitate the demonstration of the direct network request Baidu , The code is as follows ：

private static final String URL = "http://wwww.baidu.com";

3.4 Sync GET request

Sync GET The steps of the request are simple , It's mostly divided into ：

• structure OkHttpClient object ;
• structure Request object ;
• Build... From the objects in the first two steps Call object ;
• adopt call.execute() Method to submit a synchronization request . Be careful , Because it's a synchronization request , So the api To put it in a child thread , Avoid blocking the main thread , cause ANR abnormal . in addition ,Android3.0 In the future, it is not allowed to access the network in the main thread .

The code is as follows ：

private void getBySynchronized() {

btn_get_syn.setOnClickListener(new View.OnClickListener() {

@Override
public void onClick(View v) {

// 1. structure Client object 
OkHttpClient client = new OkHttpClient();
// 2. Build with builder mode and chain call Request object 
final Request request = new Request.Builder()
.url(URL) // request URL
.get() // The default is get request , Don't write 
.build();
// 3. adopt 1 and 2 Produced Client and Request Object to generate Call object 
final Call call = client.newCall(request);
// 4. The synchronous get Request needs to use execute() Method , And in order to prevent the main thread from blocking, it needs to be placed in the sub thread itself 
new Thread(new Runnable() {

@Override
public void run() {

try {

// 6. structure response object 
Response response = call.execute();
Log.d(TAG, " The synchronous get The request is successful ！ The requested information is ：" + response.body().string());
} catch (IOException e) {

e.printStackTrace();
}
}
}).start();
}
});
}

3.5 asynchronous GET request

asynchronous GET The first few steps of the request are the same as synchronization , Just the last one is through call.enqueue(Callback()) To submit a request , The code is as follows ：

private void getByAsynchronized() {

btn_get_asy.setOnClickListener(new View.OnClickListener() {

@Override
public void onClick(View v) {

// 1. structure Client object 
OkHttpClient client = new OkHttpClient();
// 2. Build with builder mode and chain call Request object 
final Request request = new Request.Builder()
.url(URL) // request URL
.get() // The default is get request , Don't write 
.build();
// 3. adopt 1 and 2 Produced Client and Request Object to generate Call object 
Call call = client.newCall(request);
// 4. call Call Object's enqueue() Method , And implement a callback implementation class 
call.enqueue(new Callback() {

@Override
public void onFailure(@NotNull Call call, @NotNull IOException e) {

Log.d(TAG, " Send asynchronously get request was aborted ！");
e.printStackTrace();
}
@Override
public void onResponse(@NotNull Call call, @NotNull Response response) throws IOException {

Log.d(TAG, " Send asynchronously get The request is successful ！ The requested information is ：" + response.body().string());
}
});
}
});
}

3.6 Sync POST request

Sync POST The requested steps are similar to synchronization GET request , It's mostly divided into ：

• structure OkHttpClient object ;
• structure FormBody object （ Key value pair ）
• structure Request object ;
• Build... From the objects in the first two steps Call object ;
• adopt call.execute() Method to submit a synchronization request .

The code is as follows ：

private void postBySynchronized() {

btn_post_syn.setOnClickListener(new View.OnClickListener() {

@Override
public void onClick(View v) {

// 1. structure Client object 
OkHttpClient client = new OkHttpClient();
// 2. Use builder mode and chain call to build key value pair object 
FormBody formBody = new FormBody.Builder()
.add("username", "admin")
.add("password", "123456")
.build();
// 3. Build with builder mode and chain call Request object 
final Request request = new Request.Builder()
.url(URL) // request URL
.post(formBody) // The default is get request , Don't write 
.build();
// 4. adopt 1 and 3 Produced Client and Request Object to generate Call object 
final Call call = client.newCall(request);
// 5. The synchronous post Request needs to use execute() Method , And in order to prevent the main thread from blocking, it needs to be placed in the sub thread itself 
new Thread(new Runnable() {

@Override
public void run() {

try {

// 6. structure response object 
Response response = call.execute();
Log.d(TAG, " The synchronous post The request is successful ！ The requested information is ：" + response.body().string());
} catch (IOException e) {

e.printStackTrace();
}
}
}).start();
}
});
}

3.7 asynchronous POST request

asynchronous POST The first few steps of the request are the same as synchronization , Just the last one is through call.enqueue(Callback()) To submit a request , The code is as follows ：

private void postByAsynchronized() {

btn_post_asy.setOnClickListener(new View.OnClickListener() {

@Override
public void onClick(View v) {

// 1. structure Client object 
OkHttpClient client = new OkHttpClient();
// 2. Use builder mode and chain call to build key value pair object 
FormBody formBody = new FormBody.Builder()
.add("username", "admin")
.add("password", "123456")
.build();
// 3. Build with builder mode and chain call Request object 
final Request request = new Request.Builder()
.url(URL) // request URL
.post(formBody) // The default is get request , Don't write 
.build();
// 4. adopt 1 and 3 Produced Client and Request Object to generate Call object 
Call call = client.newCall(request);
// 5. call Call Object's enqueue() Method , And implement a callback implementation class 
call.enqueue(new Callback() {

@Override
public void onFailure(@NotNull Call call, @NotNull IOException e) {

Log.d(TAG, " Send asynchronously post request was aborted ！");
e.printStackTrace();
}
@Override
public void onResponse(@NotNull Call call, @NotNull Response response) throws IOException {

Log.d(TAG, " Send asynchronously post The request is successful ！ The requested information is ：" + response.body().string());
}
});
}
});
}

4 summary

• A synchronous invocation ： Write simple , But it will block the main thread , Generally not applicable
• Asynchronous call ： The callback function is in the child thread , We can't update... In a child thread UI, It needs help from runOnUiThread() Methods or Handler To deal with it

Generally speaking , Although synchronization / Asynchronous calls have their own advantages and disadvantages , In the actual project , We are still Asynchronous call It's going to be used a little bit more , collocation RxJava/RxAndroid as well as EventBus, Can enhance the user experience . Of course , If it's for rapid development, it's simpler demo, A synchronous invocation That's enough. .

5. Source code address

AFL——Android Frame learning