Android 网络编程

本章节将介绍Android网络编程的核心知识点，包括常用网络库、协议解析、安全性等方面。

HTTP/HTTPS基础

核心概念

HTTP请求方法（GET、POST、PUT、DELETE等）
HTTP状态码
HTTP请求/响应头
HTTPS的工作原理

安全机制

// 配置SSL证书
val sslContext = SSLContext.getInstance("TLS")
val trustManagerFactory = TrustManagerFactory.getInstance(TrustManagerFactory.getDefaultAlgorithm())
trustManagerFactory.init(keyStore)
sslContext.init(null, trustManagerFactory.trustManagers, null)

OkHttp使用

基本配置

// OkHttpClient配置
val client = OkHttpClient.Builder()
    .connectTimeout(10, TimeUnit.SECONDS)
    .readTimeout(10, TimeUnit.SECONDS)
    .writeTimeout(10, TimeUnit.SECONDS)
    .addInterceptor(HttpLoggingInterceptor().apply {
        level = HttpLoggingInterceptor.Level.BODY
    })
    .build()

拦截器

应用拦截器
网络拦截器
自定义拦截器

// 自定义拦截器
class TokenInterceptor : Interceptor {
    override fun intercept(chain: Interceptor.Chain): Response {
        val original = chain.request()
        val request = original.newBuilder()
            .header("Authorization", "Bearer $token")
            .build()
        return chain.proceed(request)
    }
}

Retrofit使用

接口定义

interface ApiService {
    @GET("users/{id}")
    suspend fun getUser(
        @Path("id") userId: String
    ): Response<User>
 
    @POST("users")
    suspend fun createUser(
        @Body user: User
    ): Response<User>
}

配置示例

// Retrofit构建
val retrofit = Retrofit.Builder()
    .baseUrl(BASE_URL)
    .client(okHttpClient)
    .addConverterFactory(GsonConverterFactory.create())
    .build()
 
val apiService = retrofit.create(ApiService::class.java)

缓存策略

网络缓存

// 配置缓存
val cacheDir = File(context.cacheDir, "http_cache")
val cache = Cache(cacheDir, 10 * 1024 * 1024) // 10MB
 
val client = OkHttpClient.Builder()
    .cache(cache)
    .addNetworkInterceptor { chain ->
        val response = chain.proceed(chain.request())
        response.newBuilder()
            .header("Cache-Control", "public, max-age=60")
            .build()
    }
    .build()

离线缓存

// 离线缓存拦截器
class OfflineCacheInterceptor(private val context: Context) : Interceptor {
    override fun intercept(chain: Interceptor.Chain): Response {
        var request = chain.request()
        if (!isNetworkAvailable(context)) {
            request = request.newBuilder()
                .header("Cache-Control", "public, only-if-cached, max-stale=2419200")
                .build()
        }
        return chain.proceed(request)
    }
}

性能优化

连接池复用
请求合并
图片压缩
断点续传

示例代码

// 连接池配置
val connectionPool = ConnectionPool(
    maxIdleConnections = 5,
    keepAliveDuration = 5,
    timeUnit = TimeUnit.MINUTES
)
 
val client = OkHttpClient.Builder()
    .connectionPool(connectionPool)
    .build()

错误处理

网络异常

超时处理
重试机制
错误统一处理

// 统一错误处理
sealed class NetworkResult<T> {
    data class Success<T>(val data: T) : NetworkResult<T>()
    data class Error<T>(val code: Int, val message: String) : NetworkResult<T>()
    class Loading<T> : NetworkResult<T>()
}
 
// 网络请求封装
suspend fun <T> safeApiCall(
    apiCall: suspend () -> Response<T>
): NetworkResult<T> {
    return try {
        val response = apiCall()
        if (response.isSuccessful) {
            NetworkResult.Success(response.body()!!)
        } else {
            NetworkResult.Error(response.code(), response.message())
        }
    } catch (e: Exception) {
        NetworkResult.Error(-1, e.message ?: "Unknown error")
    }
}

Type System Security