使用 class Kotlin Android 解析 json 时出错

Question

hi i am trying to parse JSON with kotlin

below is my json code

    [{
    "module":"1",
    "books":[{"name":"bookname1","authors":"author1, author 2"},
             {"name":"bookname2","authors":"author1, author 2"},
             {"name":"bookname3","authors":"author1, author 2"}]
},
{
    "module":"2",
    "books":[{"name":"bookname1","authors":"author1, author 2"},
             {"name":"bookname2","authors":"author1, author 2"},
             {"name":"bookname3","authors":"author1, author 2"}]
},
{
    "module":"3",
    "books":[{"name":"bookname1","authors":"author1, author 2"},
             {"name":"bookname2","authors":"author1, author 2"},
             {"name":"bookname3","authors":"author1, author 2"}]
},
{
    "module":"4",
    "books":[{"name":"bookname1","authors":"author1, author 2"},
             {"name":"bookname2","authors":"author1, author 2"},
             {"name":"bookname3","authors":"author1, author 2"}]
},
{
    "module":"5",
    "books":[{"name":"bookname1","authors":"author1, author 2"},
             {"name":"bookname2","authors":"author1, author 2"},
             {"name":"bookname3","authors":"author1, author 2"}]
}]

please note that this json response starts with array

here is my class to parse it

class SemdetailsPArser {

    @SerializedName("module")
    @Expose
    var module: String? = null
    @SerializedName("books")
    @Expose
    var books: List<Book>? = null




}

class Book {

    @SerializedName("name")
    @Expose
    var name: String? = null
    @SerializedName("authors")
    @Expose
    var authors: String? = null

}

And here is my code

//interface

interface SemdetailsFetcher {
    @GET("test/json/sub1.json")
    fun getCurrentSemData(): Call<SemdetailsPArser>
}

here is my code in activity

fun getCurrentData() {
        val retrofit = Retrofit.Builder()
            .baseUrl(BaseUrl)
            .addConverterFactory(GsonConverterFactory.create())
            .build()
        val service = retrofit.create(SemdetailsFetcher::class.java)
        val call = service.getCurrentSemData()
        call.enqueue(object : Callback, retrofit2.Callback<SemdetailsPArser> {
            override fun onResponse(
                call: retrofit2.Call<SemdetailsPArser>?,
                response: retrofit2.Response<SemdetailsPArser>?
            ) {
               // val thisthig = response?.body();
                println("here 1 ${response?.body().toString()}")
            }

            override fun onFailure(call: Call?, e: IOException?) {
                println("here 2")
            }

            override fun onFailure(call: retrofit2.Call<SemdetailsPArser>?, t: Throwable?) {
                println("here 3 $t")
            }

            override fun onResponse(call: Call, response: Response) {
                if (response.code() == 200) {

                    println("secodn success")
                    val sampleResp = response.body()!!

                    println(sampleResp)
                }
            }


        })
    }

and i am getting this error

here 3 com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected BEGIN_OBJECT but was BEGIN_ARRAY at line 1 column 2 path $

I understood that this might be related to my parsing class

here i am getting an array of json info, i tried the same code with another json

{
    "person": {
        "name": "Don",
        "age": 35
    },
    "books": [{
            "id": 800,
            "name": "book 1",
            "description": "clear sky",
            "icon": "01n"
        },
        {
            "id": 801,
            "name": "book 2",
            "description": "clear sky 1",
            "icon": "01N"
        }
    ],

    "city": "bgvnslsl",
    "id": 1851632,
    "bname": "abcd",
    "code": 200
}

this was working perfectly when i changed the parsing class and interface

My problem is that i dont know how to write a class to parse a json response starting with an array

Answer 1

You are expecting list of SemdetailsPArser , so you should define return type as List of SemdetailsPArser

This should fix problem.

interface SemdetailsFetcher {
    @GET("test/json/sub1.json")
    fun getCurrentSemData(): Call<List<SemdetailsPArser>>
}

You also need to change it in other parts of code.

Answer 2

The error you are getting means that you're trying to parse JSON array, thinking it should be JSON object. JSON array is the thing between these [] , while JSON object is in curly brackets like these {} . So your first JSON corresponds to something like List<Module> , it's not an object, but a list of them. Each module has a list of books in it.

So all said, it should be like this

interface SemdetailsFetcher {
    @GET("test/json/sub1.json")
    fun getCurrentSemData(): Call<List<SemdetailsPArser>>
}

By the way, if you define your POJOs right, you won't need all the annotations.

Answer 3

Create SemdetailsPArser class

data class SemdetailsPArser( val books: List<Book>, val module: String )

Next create Book class

data class Book(
val authors: String,
val name: String

)

next in the interface (SemdetailsFetcher)

interface SemdetailsFetcher {
@GET("test/json/sub1.json")
fun getCurrentSemData(): Call<List<SemdetailsPArser>>

}