Android Retrofit2 관련 설정 총 정리 (HTTP 통신, Gson paring)

                                    CLEARTEXT communication to localhost not permitted by network security policy

                                    오류 원인: 안드로이드 API 버전에 따른 HTTP 통신 지원 X : HTTPS로만 (Android9: API LEVEL 28부터)

                                    해결 방안:

1. network_security_config.xml 파일 생성 : res/xml 경로

아래 코드를 넣는다.
<?xml version="1.0" encoding="utf-8"?>
<network-security-config>
    <domain-config cleartextTrafficPermitted="true">
        <domain includeSubdomains="true">10.0.2.2</domain>
    </domain-config>
</network-security-config>

                                    💡 Android에서는 Localhost로 요청을 전송하는 것이 아닌 10.0.2.2:port로
로컬 서버에 요청을 보낼 수 있습니다.

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

<application?
    android:networkSecurityConfig="@xml/network_security_config"
</application>

                                    Expected BEGIN_OBJECT but was STRING at line 1 column
  96path: $.boradResults[0].createdAt

                                    현재 포스팅 데이터를 BoardResult로 받고 있는데, Gson에서 parsing할 수 없어서 발생하는 오류

                                    package com.example.myapplication.dto

import java.time.LocalDateTime

data class BoardResult(
    val id: Long,

    val writerName: String,

    val textContent: String,

    val fileApiUrl: String?,

    val createdAt: LocalDateTime,

    val lastModifiedAt: LocalDateTime, // Gson에서 parsing이 안됨

    val readingCount: Long,

    val commentCount:Int,

    val jsonComment: String?,

    val likeCount: Int
)

                                    class LocalDateTimeAdapter : JsonSerializer<LocalDateTime>, JsonDeserializer<LocalDateTime> {
    private val formatter = DateTimeFormatter.ISO_LOCAL_DATE_TIME

    override fun serialize(src: LocalDateTime?, typeOfSrc: Type?, context: JsonSerializationContext?): JsonElement {
        return JsonPrimitive(formatter.format(src))
    }

    @Throws(JsonParseException::class)
    override fun deserialize(json: JsonElement, typeOfT: Type, context: JsonDeserializationContext): LocalDateTime {
        return LocalDateTime.parse(json.asString, formatter)
    }
}

                                    package com.example.myapplication.di

import com.example.myapplication.utils.LocalDateTimeAdapter
import com.google.gson.Gson
import com.google.gson.GsonBuilder
import dagger.Module
import dagger.Provides
import dagger.hilt.InstallIn
import dagger.hilt.components.SingletonComponent
import okhttp3.OkHttpClient
import okhttp3.logging.HttpLoggingInterceptor
import retrofit2.Retrofit
import retrofit2.converter.gson.GsonConverterFactory
import java.time.LocalDateTime
import java.util.concurrent.TimeUnit
import javax.inject.Singleton

@Module
@InstallIn(SingletonComponent::class)
object RetrofitModule {

    @Singleton
    @Provides
    fun provideGson(): Gson {
        return GsonBuilder()
            .registerTypeAdapter(LocalDateTime::class.java, LocalDateTimeAdapter())
            .create()
    }
    // Gson에 LocalDateTimeAdpater를 등록

    @Singleton
    @Provides
    fun provideRetrofit(gson: Gson): Retrofit {

        val httpLoggingInterceptor = HttpLoggingInterceptor().apply {
            level = HttpLoggingInterceptor.Level.BODY
        }

        val okHttpClient = OkHttpClient.Builder()
            .addInterceptor(httpLoggingInterceptor)
            .readTimeout(60, TimeUnit.SECONDS)
            .connectTimeout(60, TimeUnit.SECONDS)
            .build()

        return Retrofit.Builder()
            .baseUrl("http://10.0.2.2:8080")
            .addConverterFactory(GsonConverterFactory.create(gson)) // Retrofit에 Gson등록
            .client(okHttpClient)
            .build()
    }
}