retrifit2-gson-预期的BEGIN_ARRAY但为STRING或预期的BEGIN_OBJECT但为BEGIN_ARRAY

Question

我的Retrofit2调用出现以下异常：

retrofit = new Retrofit.Builder()
                .baseUrl(Constants.URL_HOST)
                .client(okHttpClient.build())
                .addConverterFactory(GsonConverterFactory.create(gson))
                .addCallAdapterFactory(RxJava2CallAdapterFactory.create())
                .build();

学分类别：

public class Credits {

    @SerializedName("director")
    @Expose
    private List<String> director;
    @SerializedName("actor")
    @Expose
    private List<String> actor = null;
    @SerializedName("presenter")
    @Expose
    private List<String> presenter;
    @SerializedName("commentator")
    @Expose
    private String commentator;

    public List<String> getDirector() {
        return director;
    }

    public void setDirector(List<String> director) {
        this.director = director;
    }

    public List<String> getActor() {
        return actor;
    }

    public void setActor(List<String> actor) {
        this.actor = actor;
    }

    public List<String> getPresenter() {
        return presenter;
    }

    public void setPresenter(List<String> presenter) {
        this.presenter = presenter;
    }

    public String getCommentator() {
        return commentator;
    }

    public void setCommentator(String commentator) {
        this.commentator = commentator;
    }
}

Answer 1

关于为什么会发生这个错误，你是对的。它试图解析一个数组，但接收到一个字符串。至于你的数据，最好还是坚持相同的模型。这意味着：使后端也返回一个数组，即使它只包含一个演示者。

然而，是的：我们可以用自定义类型适配器来修复这个问题。这个自定义类型适配器只需签入读取部分，不管它获取的是字符串还是数组。如果它得到一个字符串，我们将其重写为列表变体。

类型适配器

null

null

结果得到的类型适配器如下所示：

public class ListFromStringTypeAdapter extends TypeAdapter<List<String>> {

    public List<String> read(JsonReader reader) throws IOException {
        if (reader.peek() == JsonToken.NULL) {
            reader.nextNull();
            return null;
        }
        if (reader.peek() == JsonToken.STRING) {
            // ** This is the part where we fix the issue **
            // If we receive a String, get this and put it in a list.
            // Result will be that item in a list.
            List<String> list = new ArrayList<>();
            list.add(reader.nextString());
            return list;
        } else {
            // Else we expect to receive the array.
            // Based on original collection implementation:
            // https://github.com/google/gson/blob/0636635cbffa08157bdbd558b1212e4d806474eb/gson/src/main/java/com/google/gson/internal/bind/CollectionTypeAdapterFactory.java
            List<String> list = new ArrayList<>();
            reader.beginArray();
            while (reader.hasNext()) {
                String value = reader.nextString();
                list.add(value);
            }
            reader.endArray();
            return list;
        }
    }

    public void write(JsonWriter writer, List<String> list) throws IOException {
        // Simply writing the array, we don't need to modify anything here.
        // Based on original collection type adapter implementation:
        // https://github.com/google/gson/blob/0636635cbffa08157bdbd558b1212e4d806474eb/gson/src/main/java/com/google/gson/internal/bind/CollectionTypeAdapterFactory.java
        if (list == null) {
            writer.nullValue();
            return;
        }
        writer.beginArray();
        for (String string : list) {
            writer.value(string);
        }
        writer.endArray();
    }
}

将类型适配器注册为最后一个，我们需要告诉Gson将此类型适配器用于List类，因此修改创建Gson对象的位置：

// Get the type token for gson
Type collectionStringType = new TypeToken<List<String>>() {}.getType();
// Create gson object
Gson gson = new GsonBuilder()
        .registerTypeAdapter(collectionStringType, new ListFromStringTypeAdapter())
        .create();