小编典典

如何从Gson将JSON对象转换为POJO

json

我正在尝试使用GSON将JSON对象转换为POJO。

JSON字串

[
  {
    "automation_project": {
      "user_id": null,
      "name": "Untitled Project",
      "updated_at": "2015-06-16T19:39:42Z",
      "group_id": 764496,
      "created_at": "2014-11-23T01:01:59Z",
      "id": 16214
    }
  },
  {
    "automation_project": {
      "user_id": null,
      "name": "newintropage",
      "updated_at": "2015-06-16T21:20:47Z",
      "group_id": 764496,
      "created_at": "2015-06-16T20:39:04Z",
      "id": 29501
    }
  }
]

与GSON一起使用的AutomationProjectsList类

public class AutomationProjectsList {

private List<AutomationProject> automationProject = new ArrayList<AutomationProject>();

public List<AutomationProject> getAutomationProject() {
    return automationProject;
}

public void setAutomationProject(List<AutomationProject> automationProject) {
    this.automationProject = automationProject;
}

@Override
public String toString() {
    return "AutomationProjectsList [automationProject=" + automationProject
            + "]";
}}

自动化项目POJO

 public class AutomationProject {

    private Object userId;   
    private Integer groupId;    
    private Integer id;    
    private String name;   
    private String updatedAt;   
    private String createdAt;

    public Object getUserId() {
        return userId;
    }

    public void setUserId(Object userId) {
        this.userId = userId;
    }

    public Integer getGroupId() {
        return groupId;
    }

    public void setGroupId(Integer groupId) {
        this.groupId = groupId;
    }

    public Integer getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getUpdatedAt() {
        return updatedAt;
    }

    public void setUpdatedAt(String updatedAt) {
        this.updatedAt = updatedAt;
    }

    public String getCreatedAt() {
        return createdAt;
    }

    public void setCreatedAt(String createdAt) {
        this.createdAt = createdAt;
    }}

我正在使用的代码

JSONArray jsonArray =新的JSONArray(response.getEntity(String.class));

    for(int i = 0; i < jsonArray.length(); i++){
        if(jsonArray.get(i) instanceof JSONObject){
            JSONObject jsnObj = (JSONObject)jsonArray.get(i);               
            AutomationProjectsList obj = new Gson().fromJson(jsnObj.toString(), AutomationProjectsList.class);                  
            System.out.println(obj.getAutomationProject().get(0).getId());
        }
    }

但是它给出了一个例外:

Exception in thread "main" java.lang.IndexOutOfBoundsException: Index: 0, Size: 0
at java.util.ArrayList.rangeCheck(ArrayList.java:653)
at java.util.ArrayList.get(ArrayList.java:429)
at br.usp.icmc.teste.ConnectionRestClient.getBrowserStackProjects(ConnectionRestClient.java:74)
at br.usp.icmc.teste.TestePrincipal.main(TestePrincipal.java:9)

为什么会收到IndexOutOfBoundsException异常?我哪里错了?


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2020-07-27

共1个答案

小编典典

您的课程或JSON不正确。我建议您使用JSON。与POJO类匹配的JSON为:

{
  "automationProjects":[
    {
      "user_id": null,
      "name": "Untitled Project",
      "updated_at": "2015-06-16T19:39:42Z",
      "group_id": 764496,
      "created_at": "2014-11-23T01:01:59Z",
      "id": 16214
    },
    {
      "user_id": null,
      "name": "newintropage",
      "updated_at": "2015-06-16T21:20:47Z",
      "group_id": 764496,
      "created_at": "2015-06-16T20:39:04Z",
      "id": 29501
    }
  ]
}

请注意,我为列表使用了名称AutomationProjects,因为它更有意义,因此您的类将是:

public class AutomationProjectsList {

    private List<AutomationProject> automationProjects = new ArrayList<AutomationProject>();

    public List<AutomationProject> getAutomationProjects() {
        return automationProjects;
    }

    public void setAutomationProjects(List<AutomationProject> automationProjects) {
        this.automationProjects = automationProjects;
    }

    @Override
    public String toString() {
        return "AutomationProjectsList [automationProject=" + automationProject
        + "]";
    }
}

最后将JSON转换为AutomationProjectsList对象:

AutomationProjectsList projectsList = new Gson().fromJson(jsonArray.toString(), AutomationProjectsList.class);

然后,如果要记录每个项目:

for(AutomationProject project : projectsList.automationProjects){
  System.out.println(porject.getId());
}

总之,您的代码似乎存在以下问题:

  1. 您有列表列表还是仅一个项目列表?如果列表只是一个,为什么要jsonArray像它的子对象就是列表一样进行迭代呢?

  2. 如果您在JSON上正确建模您的类,则无需迭代JSON即可获取对象

  3. 您发布的JSON非常奇怪,并且不易与Gson一起使用,这是一项要求还是可以根据需要进行编辑?

希望这可以帮助

编辑

既然您声明无法更改所获取的JSON,那么它将变得更加复杂,但是一切都取决于对JSON格式的类进行建模。因此,让我们从这个JSON开始:

[
    {
        "automation_project": {
            "user_id": null,
            "name": "Untitled Project",
            "updated_at": "2015-06-16T19:39:42Z",
            "group_id": 764496,
            "created_at": "2014-11-23T01:01:59Z",
            "id": 16214
        }
    },
    {
        "automation_project": {
            "user_id": null,
            "name": "newintropage",
            "updated_at": "2015-06-16T21:20:47Z",
            "group_id": 764496,
            "created_at": "2015-06-16T20:39:04Z",
            "id": 29501
        }
    }
]

现在,这很讨厌,但是让我们看看这里有什么:我们有一个具有单个属性的未命名对象数组,"automationProject"这是我们的实际AutomationProject对象。因此,就结构而言,它是包装实际AutomationProject的对象列表。

因此,您将需要摆脱AutomationProjectList并使用看起来更有意义的AutomationProjectWrapper对其进行更改:

public class AutomationProjectsWrapper {

    private AutomationProject automation_project = new AutomationProject();

    public AutomationProject getAutomationProject() {
        return automation_project;
    }

    public void setAutomationProject(AutomationProject automationProject) {
        this.automation_project = automationProject;
    }

    @Override
    public String toString() {
        return "AutomationProjectsList [automationProject=" + automation_project
        + "]";
    }
}

请参阅此类等同于JSON对象:

{
    "automation_project": {
        "user_id": null,
        "name": "Untitled Project",
        "updated_at": "2015-06-16T19:39:42Z",
        "group_id": 764496,
        "created_at": "2014-11-23T01:01:59Z",
        "id": 16214
    }
}

最终,您将得到一个数组包装对象,如jsonArray,因此您可以编写:

AutomationProjectWrapper[] projectsList = new Gson().fromJson(jsonArray.toString(), AutomationProjectWrapper[].class);

然后记录您的对象:

for(AutomationProjectWrapper wrapper : projectsList){
    System.out.println(wrapper.getAutomationProject().getId());
}

编辑2

抱歉,该错误在AutomationProjectWrapper课堂上AutomationProject应命名为automation_project。已在上面的代码中修复。

2020-07-27