将JSON解析为java对象
我试图通过从JSON文件中检索类别项列表来将JSON解析为java对象,但出现如下错误: 错误:将JSON解析为java对象,java,json,Java,Json,我试图通过从JSON文件中检索类别项列表来将JSON解析为java对象,但出现如下错误: 错误: Exception in thread "main" com.fasterxml.jackson.databind.JsonMappingException: Can not deserialize instance of java.util.ArrayList out of START_OBJECT token at [Source: java.io.StringReader@6be46
Exception in thread "main" com.fasterxml.jackson.databind.JsonMappingException: Can not deserialize instance of java.util.ArrayList out of START_OBJECT token
at [Source: java.io.StringReader@6be46e8f; line: 1, column: 1]
以下是检索类别对象的代码:
public ArrayList<Category> getAllTasksFromFile(String jsonString) throws JsonParseException, JsonMappingException, IOException {
ObjectMapper mapper = new ObjectMapper();
mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
ArrayList<Category> allTasks = mapper.readValue(jsonString, new TypeReference<ArrayList<Category>>() {});
return allTasks;
Category.java
public class Category {
private List<Task> task;
private List<Task> floatTask;
private List<Task> event;
public List<Task> getTask() {
return task;
}
public void setTask(List<Task> task) {
this.task = task;
}
public List<Task> getFloat() {
return floatTask;
}
public void setTaskType(List<Task> floatTask) {
this.floatTask = floatTask;
}
public List<Task> getEvent() {
return event;
}
public void setEvent(List<Task> event) {
this.event = event;
}
}
有人知道问题出在哪里吗?我需要检索类别列表。首先,您需要一个包含类别列表的包装器。并且您的方法应该期望该包装器的列表 这是包装纸
import java.util.List;
public class CategoryWrapper {
private List<Category> category;
public List<Category> getCategory() {
return category;
}
public void setCategory(List<Category> category) {
this.category = category;
}
}
我们定义了我们的CategoryWrapper
来表示该对象。根据你的JSON分类
也是一个对象数组。然后创建Category
来表示该对象
[ {
"category" : [{...},{...}...]
} ]
Category
有三个不同的属性,分别命名为task
、floatTask
和event
。每个属性也由对象数组表示
[ {
"category" : [{
"task":[{...},{...}...],
"floatTask":[{...},{...}...],
"event":[{...},{...}...]
},
{...}
]
} ]
该对象在java中定义为Task
。每个任务
都有一些属性,如提醒、结束日期等
[ {
"category" : [{
"task":[{
"reminder" : 123,
"endDate" : "-1",
"name" : "Do homework",
"description" : "Do it now",
"startTime" : -1,
"endTime" : -1,
"priority" : 5,
"isDone" : false,
"startDate" : "-1"
}],
"floatTask":[{...},{...}...],
"event":[{...},{...}...]
},
{...}
]
} ]
它们中的每一个都可以显示为java对象。您不需要创建更多的类。请描述您希望如何将JSON映射到
ArrayList>
。我希望有一个类别列表(具有不同的类别名称),其中每个类别包含3种类型的任务列表-任务、浮动任务和事件。每个列表都包含名为Task的对象。我已经更新了JSON代码供您参考;因为我怀疑这可能是错误的。抱歉,因为今天是我第一次学习JSON。问题是您的JSON没有映射到ArrayList
,甚至没有关闭。描述JSON的每个嵌套成员以及它与ArrayList
的关系,你会发现你的问题。我也有类似的问题
[ {
"category" : ...
} ]
[ {
"category" : [{...},{...}...]
} ]
[ {
"category" : [{
"task":[{...},{...}...],
"floatTask":[{...},{...}...],
"event":[{...},{...}...]
},
{...}
]
} ]
[ {
"category" : [{
"task":[{
"reminder" : 123,
"endDate" : "-1",
"name" : "Do homework",
"description" : "Do it now",
"startTime" : -1,
"endTime" : -1,
"priority" : 5,
"isDone" : false,
"startDate" : "-1"
}],
"floatTask":[{...},{...}...],
"event":[{...},{...}...]
},
{...}
]
} ]