Android network access tutorial

1. Concept

HttpClient	Removed in Android 6 (difficult to expand the number of APIs).
HttpURLConnection	Currently officially integrated.
OKHttp	Produced by Square, the realization of underlying communications.
Retrofit	Produced by Square, the packaging of the upper-level interface makes it more convenient to use object-oriented thinking for network operations.

2. Use

Android 9 has only allowed HTTPS-type network requests by default, and HTTP plaintext transmission is no longer supported due to security risks. If you insist on using it, you need to configure it: Right-click the res directory → New → Directory → Create an xml directory, Right-click the xml directory → New → File → Create a network_config.xml file, and the modification content is as follows:

<?xml version="1.0" encoding="utf-8"?>
<network-security-config>
    <base-config cleartextTrafficPermitted="true">
        <trust-anchors>
            <certificates src="system" />
        </trust-anchors>
    </base-config>
</network-security-config>

Manifest {
//Add network access permissions
<uses-permission android:name="" />
//Allow HTTP access
<application
android:networkSecurityConfig="@xml/network_config"
</application>
}

2.1HttpURLConnection

thread {
    var connection: HttpURLConnection? = null
    try {
        val response = StringBuilder()
        val url = URL("")
        connection = () as HttpURLConnection
         = 8000
         = 8000
        //GET request        val input = 
        val reader = BufferedReader(InputStreamReader(input))
         { (it) }
        print(())
        //POST request         = "POST"
        val output = DataOutputStream()
        ("username=admin&amp;password=123456")
    } catch (e: Exception) {
        ()
    } finally {
        connection?.disconnect()
    }
}

2.2OKHttp

Portal

2.3Retrofit

View the latest version

implementation '.retrofit2:retrofit:2.9.0' //OkHttp and Okio will be downloaded together
implementation '.retrofit2:converter-gson:2.k6.1' //GSON will be downloaded together

2.3.1 Defining entity classes

Based on JSON content, write the corresponding entity class.

data class Person(var name: String, var age: Int)

2.3.2 Defining API Interface

According to the API interface, write the corresponding access file. Naming usually starts with a function name + ends with a service.

@GET	Get data from the server
@POST	Submit data to the server
@PUT @PATCH	Modify data on the server
@DELETE	Delete data on the server

interface PersonService {
    //Interface 1:/    @GET("")    // means that the GET request is initiated, the address of the incoming request (relative path, repeated root path is configured later)    fun getPerson(): Call&lt;list&lt;Person&gt;&gt;    //The return value must be declared as the call type built in Retrofit, and the specific data type returned by the server is specified through generics    //Interface 2:/<page>/    @GET("{page}/get_data.json")    //Use {page} placeholder    fun getData(@Path("page") page: Int): Call&lt;Data&gt;    //Use the @Path("page") annotation to declare the corresponding parameters    //Interface 3: /?u=<user>&t=<token>    @GET("")
    fun getData(@Query("u") user: String, @Query("t") token: String): Call&lt;Data&gt;
    //Interface 4: /v2/place?query=Beijing&token={token}&lang=zh_CN    @GET("v2/place?token=${}&amp;lang=zh_CN")    //The unchanged parameters are fixed in GET    fun searchPlaces(@Query("query") query: String): Call&lt;PlaceResponse&gt;
    //Interface 5: /data/<id>    @DELETE("data/{id}")
    fun deleteData(@Path("id") id: String): Call&lt;ResponseBody&gt;    //This generic type can accept any type and will not be parsed    //Interface 6: /data/create{"id": 1, "content": "The description for this data."}    @POST("data/create")
    fun createData(@Body data: Data): Call&lt;ResponseBody&gt;    //Convert the data in the Data object into JSON format text and put it in the body part of the HTTP request    //Interface 7: /get_data.json    // User-Agent: okhttp //header parameters are key-value pairs    //      Cache-Control: max-age=0
    // Static declaration    @Headers("User-Agent: okhttp", "Cache-Control: max-age=0")
    @GET("get_data.json")
    fun getData(): Call&lt;Data&gt;
    // Dynamic statement    @GET("get_data.json")
    fun getData(@Header("User-Agent") userAgent: String, @Header("Cache-Control") cacheControl: String): Call&lt;Data&gt;
}

2.3.3 Building Retrofit Objects

val retrofit = ()
    .baseUrl("/")    //Configure duplicate root path    .addConverterFactory(())    //Specify the conversion library to use to parse the data (here is Gson)    .build()

2.3.4 Create an API interface instance and call access functions

//Create a dynamic proxy objectval personService = (PersonService::)
//Calling access function().enqueue(object : Call&lt;List&lt;person&gt;&gt; {    //Can network request based on the address configured in the annotation    override fun onResponse(call: Call&lt;List&lt;person&gt;&gt;, response: Response&lt;List&lt;person&gt;&gt;) {
        val list = ()    //Get parsed object    }
    override fun onFailure(call: Call&lt;List&lt;person&gt;&gt;, t: Trouble) {
        ()
    }
})

2.3.5 Optimization

object GlobalRetrofit {
    private const val BASE_URL = "/"
    val retrofit: Retrofit = ()
        .baseUrl(BASE_URL)
        .addConverterFactory(())
        .build()
    //fun &lt;T&gt; create(serviceClass: Class&lt;T&gt;): T = (serviceClass)
    inline fun &lt;reified T&gt; create(): T = create(T::)
}
//useval personService = &lt;PersonService&gt;()

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