使用Ktor进行HTTP请求

绝地灬酷狼 2023-07-12 03:50 14阅读 0赞

# Ktor是什么? #

--------------------

Ktor 这是一个 Kotlin 官方打造的 Web 框架，除了提供 HTTP 服务外，Ktor 还为和客户端提供了配套的库，用来进行 HTTP 请求。当然我们已经有`Retrofit`等其他库完成类似功能，但是作为Kotlin亲儿子，`Ktor`与`Coroutine`的搭配更加天衣无缝。

接下来我们通过一个小例子学习一下Ktor在Android上的使用。

# gradle #

--------------------

`Retrofit`一样，`Ktor`在HTTP通信、JSON解析等功能模块提供了多个可选项，我们选择使用`okhttp`和[Kotlinx.Serialization][]

dependencies { 
        implementation "io.ktor:ktor-client-core:1.3.1"
        implementation "io.ktor:ktor-client-android:1.3.1"
        implementation "io.ktor:ktor-client-okhttp:1.3.1"
        implementation "io.ktor:ktor-client-serialization-jvm:1.3.1"
    }

## coroutine ##

dependencies { 
        implementation "org.jetbrains.kotlinx:kotlinx-coroutines-android:1.3.3"
    }

## serialization ##

dependencies { 
            classpath 'com.android.tools.build:gradle:3.6.1'
            classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
            classpath "org.jetbrains.kotlin:kotlin-serialization:$kotlin_version"
        }

apply plugin: 'kotlinx-serialization'
    
    dependencies { 
        implementation "org.jetbrains.kotlinx:kotlinx-serialization-runtime:0.20.0"
    }

# API #

--------------------

通过[OpenWeather][] 提供的API获取天气信息

# ViewModel #

--------------------

基于MVVM开发，`ViewModel`封装HTTP请求，将返回的数据通过`LiveData`通知到UI

## HttpClient ##

基于`Okhttp`创建一个HttpClient ，整个代码非常DSL

private val httpClient = HttpClient(OkHttp) { 
            install(JsonFeature) { 
                serializer = KotlinxSerializer(
                    Json(
                        JsonConfiguration.Stable.copy()
                    )
                )
            }
        }

通过httpClient就可以进行http请求了。

## LiveData ##

`viewModelScope.launch` 开启协程，`httpClient.post`进行异步请求。

val openWeatherMapLiveData = MutableLiveData<OpenWeatherMapJson>()
    
        fun getOpenWeatherMapJson() { 
            viewModelScope.launch { 
                try { 
                    val openWeatherMapJson = httpClient.post<OpenWeatherMapJson>("https://api.openweathermap.org/data/2.5/weather?q=yokohama&appid={KEY}") { 
                        contentType(ContentType.Application.Json)
                    }
                    openWeatherMapLiveData.postValue(openWeatherMapJson)
                } catch (e:Exception) { 
                    Log.e("w", e.message)
                }
            }
        }

# Model #

--------------------

JSON解析后得到以下data class

@Serializable
    data class OpenWeatherMapJson(
        val coord: Coord,
        val weather: List<Weather>,
        val base: String,
        val main: Main,
        val visibility: Int,
        val wind: Wind,
        val clouds: Clouds,
        val dt: Int,
        val sys: Sys,
        val timezone: Int,
        val id: Int,
        val name: String,
        val cod: Int
    )

# View(Activity) #

--------------------

订阅ViewModel，获取数据后更新View

class MainActivity : AppCompatActivity() { 
    
        private val viewModel by viewModels<MainViewModel>()
    
        override fun onCreate(savedInstanceState: Bundle?) { 
            super.onCreate(savedInstanceState)
            setContentView(R.layout.activity_main)
            setSupportActionBar(toolbar)
    
            fab.setOnClickListener {  view ->
                viewModel.getOpenWeatherMapJson()
            }
            viewModel.openWeatherMapLiveData.observe(this, Observer { 
                textView.text = it.name
            })
        }
    }

# 总结 #

--------------------

虽然`retrofit`现在也支持`Coroutine`的使用，但是`Ktor`中使用`Coroutine`的成本更低，而且Ktor支持Kotlin MPP，当有跨平台需求时Ktor绝对是一个好选择。

[Kotlinx.Serialization]: https://blog.csdn.net/vitaviva/article/details/104779479
[OpenWeather]: https://openweathermap.org/