Android 網絡開發核心知識點

一、基礎網絡通信

1. HTTP/HTTPS 協議

• HTTP方法：GET、POST、PUT、DELETE等
• 狀態碼：200(成功)、404(未找到)、500(服務器錯誤)等
• HTTPS加密：SSL/TLS握手過程
• 報文結構：請求頭/響應頭、請求體/響應體

2. 網絡請求權限

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

3. 檢查網絡狀態

val connectivityManager = getSystemService(CONNECTIVITY_SERVICE) as ConnectivityManager
val activeNetwork = connectivityManager.activeNetwork
val capabilities = connectivityManager.getNetworkCapabilities(activeNetwork)
val isConnected = capabilities?.hasCapability(NET_CAPABILITY_INTERNET) ?: false

二、網絡請求實現方式

1. HttpURLConnection

val url = URL("https://api.example.com/data")
val connection = url.openConnection() as HttpURLConnection
try {connection.requestMethod = "GET"val inputStream = connection.inputStreamval response = inputStream.bufferedReader().use { it.readText() }
} finally {connection.disconnect()
}

2. OkHttp (最常用)

// 添加依賴
implementation("com.squareup.okhttp3:okhttp:4.9.3")// 使用示例
val client = OkHttpClient()
val request = Request.Builder().url("https://api.example.com/data").build()client.newCall(request).enqueue(object : Callback {override fun onResponse(call: Call, response: Response) {val responseData = response.body?.string()}override fun onFailure(call: Call, e: IOException) {// 處理錯誤}
})

3. Retrofit (REST API 最佳選擇)

// 添加依賴
implementation("com.squareup.retrofit2:retrofit:2.9.0")
implementation("com.squareup.retrofit2:converter-gson:2.9.0")// 定義API接口
interface ApiService {@GET("users/{id}")suspend fun getUser(@Path("id") userId: String): User
}// 創建Retrofit實例
val retrofit = Retrofit.Builder().baseUrl("https://api.example.com/").addConverterFactory(GsonConverterFactory.create()).build()val service = retrofit.create(ApiService::class.java)// 發起請求(Coroutine方式)
lifecycleScope.launch {try {val user = service.getUser("123")} catch (e: Exception) {// 處理錯誤}
}

三、數據解析

1. JSON 解析

• Gson：

  val gson = Gson()
  val user = gson.fromJson(jsonString, User::class.java)
  val json = gson.toJson(user)
  

• Moshi：

  val moshi = Moshi.Builder().build()
  val jsonAdapter = moshi.adapter(User::class.java)
  val user = jsonAdapter.fromJson(jsonString)
  val json = jsonAdapter.toJson(user)
  

2. XML 解析

• Pull Parser：

  val parser = Xml.newPullParser()
  parser.setInput(inputStream, null)
  var eventType = parser.eventType
  while (eventType != XmlPullParser.END_DOCUMENT) {when (eventType) {XmlPullParser.START_TAG -> { /* 處理開始標簽 */ }XmlPullParser.TEXT -> { /* 處理文本內容 */ }}eventType = parser.next()
  }
  

四、高級網絡特性

1. 緩存策略

val cache = Cache(File(context.cacheDir, "http_cache"), 10 * 1024 * 1024) // 10MBval client = OkHttpClient.Builder().cache(cache).addInterceptor(CacheInterceptor()).build()class CacheInterceptor : Interceptor {override fun intercept(chain: Interceptor.Chain): Response {val request = chain.request()val response = chain.proceed(request)val cacheControl = CacheControl.Builder().maxAge(30, TimeUnit.MINUTES) // 30分鐘緩存.build()return response.newBuilder().header("Cache-Control", cacheControl.toString()).build()}
}

2. 文件下載

val request = Request.Builder().url(fileUrl).build()client.newCall(request).enqueue(object : Callback {override fun onResponse(call: Call, response: Response) {response.body?.byteStream()?.use { input ->FileOutputStream(localFile).use { output ->input.copyTo(output)}}}override fun onFailure(call: Call, e: IOException) {// 處理錯誤}
})

3. 文件上傳

val requestBody = MultipartBody.Builder().setType(MultipartBody.FORM).addFormDataPart("file", file.name,file.asRequestBody("image/jpeg".toMediaType())).build()val request = Request.Builder().url(uploadUrl).post(requestBody).build()

五、網絡安全

1. 證書鎖定 (Certificate Pinning)

val hostname = "api.example.com"
val certificatePinner = CertificatePinner.Builder().add(hostname, "sha256/AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=").build()val client = OkHttpClient.Builder().certificatePinner(certificatePinner).build()

2. 網絡安全配置

<!-- res/xml/network_security_config.xml -->
<network-security-config><domain-config cleartextTrafficPermitted="false"><domain includeSubdomains="true">example.com</domain><trust-anchors><certificates src="@raw/my_ca"/></trust-anchors></domain-config>
</network-security-config><!-- AndroidManifest.xml 中引用 -->
<applicationandroid:networkSecurityConfig="@xml/network_security_config"... >

六、WebSocket 通信

val request = Request.Builder().url("wss://echo.websocket.org").build()val listener = object : WebSocketListener() {override fun onMessage(webSocket: WebSocket, text: String) {// 接收消息}override fun onClosed(webSocket: WebSocket, code: Int, reason: String) {// 連接關閉}
}val webSocket = client.newWebSocket(request, listener)// 發送消息
webSocket.send("Hello WebSocket!")

七、性能優化

1. 連接池

val client = OkHttpClient.Builder().connectionPool(ConnectionPool(5, 5, TimeUnit.MINUTES)).build()

2. 請求合并

// 使用GraphQL合并多個REST請求
// 或使用自定義攔截器合并相似請求

3. 圖片加載優化

// 使用Glide或Picasso
Glide.with(context).load(imageUrl).placeholder(R.drawable.placeholder).error(R.drawable.error).into(imageView)

八、調試工具

1. Stetho：Facebook開發的Android調試工具

   val client = OkHttpClient.Builder().addNetworkInterceptor(StethoInterceptor()).build()
   

2. Chrome DevTools：查看網絡請求

3. Charles/Fiddler：抓包工具

九、最佳實踐

1. 主線程規則：網絡請求必須在后臺線程執行
2. 錯誤處理：妥善處理各種網絡異常（超時、無網絡等）
3. 資源釋放：確保關閉所有網絡資源（InputStream等）
4. 性能考慮：
   • 減少請求次數
   • 壓縮數據
   • 使用緩存
5. 安全考慮：
   • 使用HTTPS
   • 驗證服務器證書
   • 敏感數據加密

Android網絡開發需要綜合考慮功能實現、性能優化和安全性，選擇合適的工具和架構可以使網絡層更加健壯和高效。