Android 网络开发核心知识点

Android 网络开发核心知识点

一、基础网络通信

1. HTTP/HTTPS 协议

• HTTP方法：GET、POST、PUT、DELETE等
• 状态码：200(成功)、404(未找到)、500(服务器错误)等
• HTTPS加密：SSL/TLS握手过程
• 报文结构：请求头/响应头、请求体/响应体

2. 网络请求权限

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

3. 检查网络状态

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、网络请求实现方式

1. HttpURLConnection

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

2. OkHttp (最常用)

// 添加依赖
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) {
        // 处理错误
    }
})

3. Retrofit (REST API 最佳选择)

// 添加依赖
implementation("com.squareup.retrofit2:retrofit:2.9.0")
implementation("com.squareup.retrofit2:converter-gson:2.9.0")

// 定义API接口
interface ApiService {
    @GET("users/{id}")
    suspend fun getUser(@Path("id") userId: String): User
}

// 创建Retrofit实例
val retrofit = Retrofit.Builder()
    .baseUrl("https://api.example.com/")
    .addConverterFactory(GsonConverterFactory.create())
    .build()

val service = retrofit.create(ApiService::class.java)

// 发起请求(Coroutine方式)
lifecycleScope.launch {
    try {
        val user = service.getUser("123")
    } catch (e: Exception) {
        // 处理错误
    }
}

三、数据解析

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 -> { /* 处理开始标签 */ }
          XmlPullParser.TEXT -> { /* 处理文本内容 */ }
      }
      eventType = parser.next()
  }
  

四、高级网络特性

1. 缓存策略

val cache = Cache(File(context.cacheDir, "http_cache"), 10 * 1024 * 1024) // 10MB

val 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分钟缓存
            .build()
            
        return response.newBuilder()
            .header("Cache-Control", cacheControl.toString())
            .build()
    }
}

2. 文件下载

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) {
        // 处理错误
    }
})

3. 文件上传

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、网络安全

1. 证书锁定 (Certificate Pinning)

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

val client = OkHttpClient.Builder()
    .certificatePinner(certificatePinner)
    .build()

2. 网络安全配置

<!-- 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 -->
<application
    android: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) {
        // 连接关闭
    }
}

val webSocket = client.newWebSocket(request, listener)

// 发送消息
webSocket.send("Hello WebSocket!")

七、性能优化

1. 连接池

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

2. 请求合并

// 使用GraphQL合并多个REST请求
// 或使用自定义拦截器合并相似请求

3. 图片加载优化

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

八、调试工具

1. Stetho：Facebook开发的Android调试工具

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

2. Chrome DevTools：查看网络请求

3. Charles/Fiddler：抓包工具

九、最佳实践

1. 主线程规则：网络请求必须在后台线程执行
2. 错误处理：妥善处理各种网络异常（超时、无网络等）
3. 资源释放：确保关闭所有网络资源（InputStream等）
4. 性能考虑：
   • 减少请求次数
   • 压缩数据
   • 使用缓存
5. 安全考虑：
   • 使用HTTPS
   • 验证服务器证书
   • 敏感数据加密

Android网络开发需要综合考虑功能实现、性能优化和安全性，选择合适的工具和架构可以使网络层更加健壮和高效。