如何将 JSON 字符串转换为 Java 对象列表？
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How to convert JSON string into List of Java object?
提问by Nitesh
This is my JSON Array :-
这是我的 JSON 数组：-
[
{
"firstName" : "abc",
"lastName" : "xyz"
},
{
"firstName" : "pqr",
"lastName" : "str"
}
]
I have this in my String object. Now I want to convert it into Java object and store it in List of java object. e.g. In Student object. I am using below code to convert it into List of Java object : -
我的 String 对象中有这个。现在我想将它转换为 Java 对象并将其存储在 Java 对象列表中。例如在学生对象中。我正在使用以下代码将其转换为 Java 对象列表：-
ObjectMapper mapper = new ObjectMapper();
StudentList studentList = mapper.readValue(jsonString, StudentList.class);
My List class is:-
我的列表类是：-
public class StudentList {
private List<Student> participantList = new ArrayList<Student>();
//getters and setters
}
My Student object is: -
我的学生对象是：-
class Student {
String firstName;
String lastName;
//getters and setters
}
Am I missing something here? I am getting below exception: -
我在这里错过了什么吗？我遇到以下异常：-
Exception : com.fasterxml.Hymanson.databind.JsonMappingException: Can not deserialize instance of com.aa.Student out of START_ARRAY token
采纳答案by Manos Nikolaidis
You are asking Hymanson to parse a StudentList. Tell it to parse a List(of students) instead. Since Listis generic you will typically use a TypeReference
你要求Hyman逊解析一个StudentList. 告诉它解析一个List（学生）。由于List是通用的，您通常会使用TypeReference
List<Student> participantJsonList = mapper.readValue(jsonString, new TypeReference<List<Student>>(){});
回答by Pankaj Jaiswal
You can also use Gson for this scenario.
你也可以在这个场景中使用 Gson。
Gson gson = new Gson();
NameList nameList = gson.fromJson(data, NameList.class);
List<Name> list = nameList.getList();
Your NameList class could look like:
您的 NameList 类可能如下所示：
class NameList{
List<Name> list;
//getter and setter
}
回答by monstereo
StudentList studentList = mapper.readValue(jsonString,StudentList.class);
Change this to this one
把这个改成这个
StudentList studentList = mapper.readValue(jsonString, new TypeReference<List<Student>>(){});
回答by Atul Sharma
I have resolved this one by creating the POJO class (Student.class) of the JSON and Main Class is used for read the values from the JSON in the problem.
我通过创建 JSON 的 POJO 类 (Student.class) 解决了这个问题，主类用于从问题中的 JSON 读取值。
**Main Class**
public static void main(String[] args) throws JsonParseException,
JsonMappingException, IOException {
String jsonStr = "[ \r\n" + " {\r\n" + " \"firstName\" : \"abc\",\r\n"
+ " \"lastName\" : \"xyz\"\r\n" + " }, \r\n" + " {\r\n"
+ " \"firstName\" : \"pqr\",\r\n" + " \"lastName\" : \"str\"\r\n" + " } \r\n" + "]";
ObjectMapper mapper = new ObjectMapper();
List<Student> details = mapper.readValue(jsonStr, new
TypeReference<List<Student>>() { });
for (Student itr : details) {
System.out.println("Value for getFirstName is: " +
itr.getFirstName());
System.out.println("Value for getLastName is: " +
itr.getLastName());
}
}
**RESULT:**
Value for getFirstName is: abc
Value for getLastName is: xyz
Value for getFirstName is: pqr
Value for getLastName is: str
**Student.class:**
public class Student {
private String lastName;
private String firstName;
public String getLastName() {
return lastName;
}
public String getFirstName() {
return firstName;
} }
回答by javaPlease42
I made a method to do this below called jsonArrayToObjectList. Its a handy static class that will take a filename and the file contains an array in JSON form.
我在下面创建了一个方法来执行此操作，称为jsonArrayToObjectList. 它是一个方便的静态类，它将采用文件名，并且该文件包含一个 JSON 格式的数组。
List<Items> items = jsonArrayToObjectList(
"domain/ItemsArray.json", Item.class);
public static <T> List<T> jsonArrayToObjectList(String jsonFileName, Class<T> tClass) throws IOException {
ObjectMapper mapper = new ObjectMapper();
final File file = ResourceUtils.getFile("classpath:" + jsonFileName);
CollectionType listType = mapper.getTypeFactory()
.constructCollectionType(ArrayList.class, tClass);
List<T> ts = mapper.readValue(file, listType);
return ts;
}
回答by ?ào ??c Huy
Try this. It works with me. Hope you too!
尝试这个。它和我一起工作。希望你也是！
List<YOUR_OBJECT> testList = new ArrayList<>();
testList.add(test1);
Gson gson = new Gson();
String json = gson.toJson(testList);
Type type = new TypeToken<ArrayList<YOUR_OBJECT>>(){}.getType();
ArrayList<YOUR_OBJECT> array = gson.fromJson(json, type);回答by erhun
You can use below class to read list of objects. It contains static method to read a list with some specific object type. It is included Jdk8Module changes which provide new time class supports too. It is a clean and generic class.
您可以使用下面的类来读取对象列表。它包含静态方法来读取具有某些特定对象类型的列表。它包含 Jdk8Module 更改，也提供了新的时间类支持。它是一个干净和通用的类。
List<Student> students = JsonMapper.readList(jsonString, Student.class);
Generic JsonMapper class:
通用 JsonMapper 类：
import com.fasterxml.Hymanson.databind.DeserializationFeature;
import com.fasterxml.Hymanson.databind.ObjectMapper;
import com.fasterxml.Hymanson.datatype.jdk8.Jdk8Module;
import com.fasterxml.Hymanson.datatype.jsr310.JavaTimeModule;
import java.io.IOException;
import java.util.*;
import java.util.Collection;
public class JsonMapper {
public static <T> List<T> readList(String str, Class<T> type) {
return readList(str, ArrayList.class, type);
}
public static <T> List<T> readList(String str, Class<? extends Collection> type, Class<T> elementType) {
final ObjectMapper mapper = newMapper();
try {
return mapper.readValue(str, mapper.getTypeFactory().constructCollectionType(type, elementType));
} catch (IOException e) {
throw new RuntimeException(e);
}
}
private static ObjectMapper newMapper() {
final ObjectMapper mapper = new ObjectMapper();
mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
mapper.registerModule(new JavaTimeModule());
mapper.registerModule(new Jdk8Module());
return mapper;
}
}
回答by Sobhan
For any one who looks for answer yet:
对于任何正在寻找答案的人：
1.Add Hymanson-databindlibrary to your build tools like Gradle or Maven
1.将Hymanson-databind库添加到您的构建工具中，例如 Gradle 或 Maven
2.in your Codes:
2.在您的代码中：
add:
ObjectMapper mapper = new ObjectMapper();
List<Student> studentList = new ArrayList<>();
studentList = Arrays.asList(mapper.readValue(jsonStringArray, Student[].class));
回答by Prakash Reddy
use below simple code, no need to use any library
使用下面的简单代码，无需使用任何库
String list = "your_json_string";
Gson gson = new Gson();
Type listType = new TypeToken<ArrayList<YourClassObject>>() {}.getType();
ArrayList<YourClassObject> users = new Gson().fromJson(list , listType);
