使用GSON将Java对象转换为JSON

转x33g5p2x  于2022-10-07 转载在 Java  
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在本文中，我们将创建一个使用GSON library将Java对象转换或序列化为JSON表示的示例。

Gson是一个Java库，可用于将Java对象转换为其JSON表示形式。它还可以用于将JSON字符串转换为等效的Java对象。Gson可以处理任意Java对象，包括您没有源代码的预先存在的对象。在这个例子中，我们将向您展示如何使用GSON将Java对象序列化为JSON。

GSON Maven依赖项

要在Maven2/3中使用Gson，可以通过添加以下依赖项来使用Maven Central中的Gson版本：

  1. <dependencies>
  2.     <!--  Gson: Java to Json conversion -->
  3.     <dependency>
  4.       <groupId>com.google.code.gson</groupId>
  5.       <artifactId>gson</artifactId>
  6.       <version>2.8.5</version>
  7.       <scope>compile</scope>
  8.     </dependency>
  9. </dependencies>

学生POJO类-要序列化的对象

让我们创建一个Student类，它与e1d1e1类有一对多关系。让我们创建Student和Phone类，并使用GSON将其序列化为JSON表示。

  1. class Student {
  3.     private long studentId;
  4.     private String studentName;
  5.     private Set < Phone > studentPhoneNumbers = new HashSet < Phone > (0);
  7.     public long getStudentId() {
  8.         return studentId;
  9.     }
  11.     public void setStudentId(long studentId) {
  12.         this.studentId = studentId;
  13.     }
  15.     public String getStudentName() {
  16.         return studentName;
  17.     }
  19.     public void setStudentName(String studentName) {
  20.         this.studentName = studentName;
  21.     }
  23.     public Set < Phone > getStudentPhoneNumbers() {
  24.         return studentPhoneNumbers;
  25.     }
  27.     public void setStudentPhoneNumbers(Set < Phone > studentPhoneNumbers) {
  28.         this.studentPhoneNumbers = studentPhoneNumbers;
  29.     }
  31.     @Override
  32.     public String toString() {
  33.         return "Student [studentId=" + studentId + ", studentName=" + studentName + ", studentPhoneNumbers=" +
  34.             studentPhoneNumbers + "]";
  35.     }
  37. }
  39. class Phone {
  41.     private long phoneId;
  42.     private String phoneType;
  43.     private String phoneNumber;
  45.     public Phone() {}
  47.     public Phone(String phoneType, String phoneNumber) {
  48.         this.phoneType = phoneType;
  49.         this.phoneNumber = phoneNumber;
  50.     }
  52.     public long getPhoneId() {
  53.         return phoneId;
  54.     }
  56.     public void setPhoneId(long phoneId) {
  57.         this.phoneId = phoneId;
  58.     }
  60.     public String getPhoneType() {
  61.         return phoneType;
  62.     }
  64.     public void setPhoneType(String phoneType) {
  65.         this.phoneType = phoneType;
  66.     }
  68.     public String getPhoneNumber() {
  69.         return phoneNumber;
  70.     }
  72.     public void setPhoneNumber(String phoneNumber) {
  73.         this.phoneNumber = phoneNumber;
  74.     }
  75. }

使用GSON将Java对象序列化或转换为JSON

在使用GSON将Java Object转换为JSON时，很高兴了解以下几点：

*不能用循环引用序列化对象，因为这将导致无限递归。
*Google GSON支持预先存在的对象。这意味着我们不需要用任何特殊的标记注释来注释类。
*序列化或反序列化时，默认情况下忽略瞬态字段。
*序列化时，将从输出中跳过空字段。
*反序列化时，JSON中缺少条目会导致将对象中的相应字段设置为null。
*与内部类、匿名类和本地类中的外部类对应的字段将被忽略，并且不会包含在序列化或反序列化中。

  1. package net.javaguides.gson;
  3. import java.util.HashSet;
  4. import java.util.Set;
  6. import com.google.gson.Gson;
  7. import com.google.gson.GsonBuilder;
  9. /**
  10. * 
  11. * @author Ramesh Fadatare
  12. *
  13. */
  14. public class GSONComplexObjectExample {
  15.     public static void main(String[] args) {
  16.         serializeStudentObject();
  17.     }
  19.     private static void serializeStudentObject() {
  20.         Gson gson = new GsonBuilder().setPrettyPrinting().create();
  21.         Student student = createStudent();
  22.         String jsonStr = gson.toJson(student);
  23.         System.out.println(jsonStr);
  24.     }
  26.     private static Student createStudent() {
  27.         Student student = new Student();
  28.         student.setStudentId(1000);
  29.         student.setStudentName("Ramesh");
  30.         Set < Phone > phones = new HashSet < Phone > ();
  31.         Phone phone = new Phone();
  32.         phone.setPhoneId(100);
  33.         phone.setPhoneNumber("1234567890");
  34.         phone.setPhoneType("Mobile Phone");
  35.         phones.add(phone);
  37.         Phone phone1 = new Phone();
  38.         phone1.setPhoneId(101);
  39.         phone1.setPhoneNumber("2222 3333 44");
  40.         phone1.setPhoneType("Landline Phone");
  41.         phones.add(phone1);
  43.         student.setStudentPhoneNumbers(phones);
  44.         return student;
  45.     }
  46. }

输出：

  1. {
  2.   "studentId": 1000,
  3.   "studentName": "Ramesh",
  4.   "studentPhoneNumbers": [
  5.     {
  6.       "phoneId": 100,
  7.       "phoneType": "Mobile Phone",
  8.       "phoneNumber": "1234567890"
  9.     },
  10.     {
  11.       "phoneId": 101,
  12.       "phoneType": "Landline Phone",
  13.       "phoneNumber": "2222 3333 44"
  14.     }
  15.   ]
  16. }

完整示例供参考

  1. package net.javaguides.gson;
  3. import java.util.HashSet;
  4. import java.util.Set;
  6. import com.google.gson.Gson;
  7. import com.google.gson.GsonBuilder;
  9. /**
  10. * 
  11. * @author Ramesh Fadatare
  12. *
  13. */
  14. public class GSONComplexObjectExample {
  15.     public static void main(String[] args) {
  16.         serializeStudentObject();
  17.     }
  19.     private static void serializeStudentObject() {
  20.         Gson gson = new GsonBuilder().setPrettyPrinting().create();
  21.         Student student = createStudent();
  22.         String jsonStr = gson.toJson(student);
  23.         System.out.println(jsonStr);
  24.     }
  26.     private static Student createStudent() {
  27.         Student student = new Student();
  28.         student.setStudentId(1000);
  29.         student.setStudentName("Ramesh");
  30.         Set < Phone > phones = new HashSet < Phone > ();
  31.         Phone phone = new Phone();
  32.         phone.setPhoneId(100);
  33.         phone.setPhoneNumber("1234567890");
  34.         phone.setPhoneType("Mobile Phone");
  35.         phones.add(phone);
  37.         Phone phone1 = new Phone();
  38.         phone1.setPhoneId(101);
  39.         phone1.setPhoneNumber("2222 3333 44");
  40.         phone1.setPhoneType("Landline Phone");
  41.         phones.add(phone1);
  43.         student.setStudentPhoneNumbers(phones);
  44.         return student;
  45.     }
  46. }
  48. class Student {
  50.     private long studentId;
  51.     private String studentName;
  52.     private Set < Phone > studentPhoneNumbers = new HashSet < Phone > (0);
  54.     public long getStudentId() {
  55.         return studentId;
  56.     }
  58.     public void setStudentId(long studentId) {
  59.         this.studentId = studentId;
  60.     }
  62.     public String getStudentName() {
  63.         return studentName;
  64.     }
  66.     public void setStudentName(String studentName) {
  67.         this.studentName = studentName;
  68.     }
  70.     public Set < Phone > getStudentPhoneNumbers() {
  71.         return studentPhoneNumbers;
  72.     }
  74.     public void setStudentPhoneNumbers(Set < Phone > studentPhoneNumbers) {
  75.         this.studentPhoneNumbers = studentPhoneNumbers;
  76.     }
  78.     @Override
  79.     public String toString() {
  80.         return "Student [studentId=" + studentId + ", studentName=" + studentName + ", studentPhoneNumbers=" +
  81.             studentPhoneNumbers + "]";
  82.     }
  84. }
  86. class Phone {
  88.     private long phoneId;
  89.     private String phoneType;
  90.     private String phoneNumber;
  92.     public Phone() {}
  94.     public Phone(String phoneType, String phoneNumber) {
  95.         this.phoneType = phoneType;
  96.         this.phoneNumber = phoneNumber;
  97.     }
  99.     public long getPhoneId() {
  100.         return phoneId;
  101.     }
  103.     public void setPhoneId(long phoneId) {
  104.         this.phoneId = phoneId;
  105.     }
  107.     public String getPhoneType() {
  108.         return phoneType;
  109.     }
  111.     public void setPhoneType(String phoneType) {
  112.         this.phoneType = phoneType;
  113.     }
  115.     public String getPhoneNumber() {
  116.         return phoneNumber;
  117.     }
  119.     public void setPhoneNumber(String phoneNumber) {
  120.         this.phoneNumber = phoneNumber;
  121.     }
  122. }

输出：

  1. {
  2.   "studentId": 1000,
  3.   "studentName": "Ramesh",
  4.   "studentPhoneNumbers": [
  5.     {
  6.       "phoneId": 100,
  7.       "phoneType": "Mobile Phone",
  8.       "phoneNumber": "1234567890"
  9.     },
  10.     {
  11.       "phoneId": 101,
  12.       "phoneType": "Landline Phone",
  13.       "phoneNumber": "2222 3333 44"
  14.     }
  15.   ]
  16. }

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原文链接 : https://www.javaguides.net/2018/10/convert-java-object-to-json-using-gson.html

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