Java GSON 无法解析到对象数组

Question

我有问题。我正在做一个网络电话，我在屏幕上打印了一个 json，如下所示：

{"Agents":[{"Id":"1","Owner":"Andre"},{"Id":"7","Owner":"Andre2"},{"Id":"8","Owner":"Andre"},{"Id":"9","Owner":"Alexander"},{"Id":"10","Owner":"Alexander"},{"Id":"12","Owner":"Andre"}]}

然后我用下面的代码从网上获取了json并解析成一个数组对象：

EfyWebAPI webAPI = new EfyWebAPI();
String jsonResponse = webAPI.executeQuery("www.mysite.org/test.php", "SELECT Id, Owner FROM Agents");

Gson gson = new Gson();
Agent[] agents = gson.fromJson(jsonResponse, Agent[].class);

System.out.println(agents[0].getId());

class 看起来像这样：

public class Agent {

    private int id;
    private String owner;

    public Agent(int id, String owner) {
        this.id = id;
        this.owner = owner;
    }

    public int getId() {
        return this.id;
    }

}

但是当我运行代码时，我得到以下错误：

Exception in thread "main" com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected BEGIN_ARRAY but was STRING at line 1 column 1 path $ at com.google.gson.Gson.fromJson(Gson.java:822) at com.google.gson.Gson.fromJson(Gson.java:775) at com.google.gson.Gson.fromJson(Gson.java:724) at com.google.gson.Gson.fromJson(Gson.java:696) at com.company.Main.main(Main.java:18) Caused by: java.lang.IllegalStateException: Expected BEGIN_ARRAY but was STRING at line 1 column 1 path $ at com.google.gson.stream.JsonReader.beginArray(JsonReader.java:350) at com.google.gson.internal.bind.ArrayTypeAdapter.read(ArrayTypeAdapter.java:70) at com.google.gson.Gson.fromJson(Gson.java:810) ... 4 more

为什么会发生这种情况，我该如何解决？

Answer 1

It works kind of... Instead of getting id=1, it gets id=0. I think it gets the id of the object count from the json. How does this work and why can't I parse multiple objects at once and return it into an array list or something?

JSON（或至少 GSON）总是期望一个字符串作为键（据我所知）。只要符合JSON标准JSON就可以，String后面是什么并不重要。

如果您声明类似

，您提到的内容是可能的

{"persons" : [ + 其余内容 + ]}，但我不确定您是否可以自动将其解析为 List<Agent>.

Answer 2

错误是说

Expected BEGIN_ARRAY...

因为第二个参数 (Agent[].class)，它需要 Agent-s 的有效 json 数组字符串。您的 json 字符串是一个具有键 Agents 的对象，值是 Agent 的数组。

例如，可能的解决方案是创建一个 class 名为 Agents，表示 json 对象。

public class Agents {
    private Agent[] Agents; // note the capital 'A' matches the key name in the json string

    public Agent[] getAgents() {
        return Agents;
    }

    public void setAgents(Agent[] agents) {
        this.Agents = agents;
    }
}

并调整代理class如下：

public class Agent {
    @SerializedName("Id") // note the annotated field is needed since in the json string id is Id
    private int id;

    @SerializedName("Owner") // same as id field, annotation needed, or rename owner to Owner
    private String owner;

    public Agent(int id, String owner) {
        this.id = id;
        this.owner = owner;
    }

    public int getId() {
        return this.id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public void setOwner(String owner) {
        this.owner = owner;
    }

    @Override
    public String toString() {
        return "Agent{" +
                "id=" + id +
                ", owner='" + owner + '\'' +
                '}';
    }
}

这是一个有效的演示：

public class GsonDemo {
    public static void main(String[] args) {
        String json = "{\"Agents\":[{\"Id\":\"1\",\"Owner\":\"Andre\"},{\"Id\":\"7\",\"Owner\":\"Andre2\"},{\"Id\":\"8\",\"Owner\":\"Andre\"},{\"Id\":\"9\",\"Owner\":\"Alexander\"},{\"Id\":\"10\",\"Owner\":\"Alexander\"},{\"Id\":\"12\",\"Owner\":\"Andre\"}]}";
        Gson gson = new Gson();
        Agents a = gson.fromJson(json, Agents.class);
        System.out.println(a.getAgents()[1]);
        System.out.println(a.getAgents().length);
        // Output:
        // Agent{id=7, owner='Andre2'}
        // 6
    }
}

Java GSON 无法解析到对象数组

Java GSON Failed parsing to object array

java

json

gson