如何为Java应用程序设置 GSON？
GSON 是 Google 的 JSON 解析器。它用于解析 JSON 文件并生成 JSON 文件。它有多个 API，可以将Java对象序列化为 JSON，并将 JSON 文件反序列化为Java对象。要在您的Java应用程序中使用 GSON，我们首先需要安装它。为此，我们可以在 Maven pom.xml 文件中添加 GSON jar 依赖项，也可以下载 jar 并将其添加到我们的项目中，如下所示：
pom.xml 文件如下：
com.google.code.gson
gson
2.3.1
让我们了解 Gson 如何使用各种 API 进行序列化和反序列化。
Consider XYZ company which maintains Employee information. So we have Employee class with attributes like id, name, department, salary and rating. We create a Gson instance as follows:
方法：
- 创建具有所有属性的对象并从中生成 GSON
- 使用 GsonBuilder 创建一个新的 gson 实例
执行：
方法 1：我们创建一个具有所有属性的对象并从中生成一个 GSON。
例子
Java
Gson gson = new Gson();Java
// Java Program to Create an Employee object with all
// Attributes and generate a GSON out of it
// Importing input output classes
import com.google.gson.Gson;
import java.io.*;
// Main class
class GFG {
// Main driver method
public static void main(String[] args)
{
// Creating an object of Gson class
Gson gson = new Gson();
// Creating an object of Employee class
Employee emp = new Employee();
// Attributes
emp.setName("John");
emp.setId("E00101");
emp.setDepartment("IT");
emp.setSalary(250000.00);
emp.setRating(7);
// Generating json from emp object
String empJson = gson.toJson(emp);
System.out.println("Emp json is " + empJson);
// Changing one of the attributes of emp object
emp.setDepartment("Java");
// Generating emp object from emp json
Employee empGenerated = gson.fromJson(
gson.toJson(emp), Employee.class);
// Print and display the employee been generated
System.out.println(
"Generated employee from json is "
+ empGenerated);
}
}
// Class 2
// Helper class
class Employee {
// Member variables of this class
private String id;
private String name;
private String department;
private int rating;
private double salary;
// Member functions of this class
// Method 1
public String getId() { return id; }
// Method 2
public void setId(String id) { this.id = id; }
// Method 3
public String getName() { return name; }
// Method 4
public void setName(String name) { this.name = name; }
// Method 5
public String getDepartment() { return department; }
// Method 6
public void setDepartment(String department)
{
this.department = department;
}
// Method 7
public int getRating() { return rating; }
// Method 8
public void setRating(int rating)
{
this.rating = rating;
}
// Method 9
public double getSalary() { return salary; }
// Method 10
public void setSalary(double salary)
{
this.salary = salary;
}
// Method 11
@Override public String toString()
{
return "Employee [id=" + id + ", name=" + name
+ ", department=" + department + ", rating="
+ rating + ", salary=" + salary + "]";
}
}Java
// Java Program where we will be using GsonBuilder object to
// Pretty Print the gson Contents
// Importing I/O classes
import java.io.*;
// Class 1
// Main class
class GFG {
// Main driver method
public static void main(String[] args)
{
// Creating an object of Employee class
Employee emp = new Employee();
// Attributes
emp.setId("F000101");
emp.setName("Dave");
emp.setRating(9);
emp.setDepartment("DB");
emp.setSalary(150000.00);
// Creating a GSON builder
GsonBuilder gsonBuilder = new GsonBuilder();
// Creating a GSON from GSON builder
Gson gson = gsonBuilder.create();
// Creating an employee gson using pretty printing
String empJson = gsonBuilder.setPrettyPrinting()
.create()
.toJson(emp);
// Print and display
System.out.println(
"Emp json in pretty print format:" + empJson);
// Update rating of emp object
emp.setRating(8);
Employee updatedEmp = gson.fromJson(
gson.toJson(emp), Employee.class);
// Print and displaying the updated employee
System.out.println("Updated employee is : "
+ updatedEmp);
}
}
// Class 2
// Helper class
class Employee {
// Attributes
private String id;
private String name;
private String department;
private int rating;
private double salary;
// Member methods of this class
public String getId() { return id; }
public void setId(String id) { this.id = id; }
public String getName() { return name; }
public void setName(String name) { this.name = name; }
public String getDepartment() { return department; }
public void setDepartment(String department)
{
this.department = department;
}
public int getRating() { return rating; }
public void setRating(int rating)
{
this.rating = rating;
}
public double getSalary() { return salary; }
public void setSalary(double salary)
{
this.salary = salary;
}
@Override public String toString()
{
return "Employee [id=" + id + ", name=" + name
+ ", department=" + department + ", rating="
+ rating + ", salary=" + salary + "]";
}
}输出：
// Java Program to Make Rating Attribute of Employee class
// as Transient
// Importing required classes
import java.io.*;
// Class 1
// Main class
class GFG {
// Main driver method
public static void main(String[] args)
{
// Creating an object of Gson and user-defined
// Employee class
Gson gson = new Gson();
Employee emp = new Employee();
emp.setName("Jane");
emp.setId("J01012");
emp.setDepartment("Devops");
emp.setSalary(200000.00);
emp.setRating(7);
// Generating json from emp object
String empJson = gson.toJson(emp);
System.out.println("Emp json is " + empJson);
// Changing one of the attributes of emp object
emp.setDepartment("Java");
// Generate emp object from emp json
Employee empGenerated = gson.fromJson(
gson.toJson(emp), Employee.class);
// Print and display the employee generated from
// json
System.out.println(
"Generated employee from json is "
+ empGenerated);
}
}
// Class 2
// Helper class
class Employee {
// Attributes
private String id;
private String name;
private String department;
private transient int rating;
private double salary;
// Member methods of this class
public String getId() { return id; }
public void setId(String id) { this.id = id; }
public String getName() { return name; }
public void setName(String name) { this.name = name; }
public String getDepartment() { return department; }
public void setDepartment(String department)
{
this.department = department;
}
public int getRating() { return rating; }
public void setRating(int rating)
{
this.rating = rating;
}
public double getSalary() { return salary; }
public void setSalary(double salary)
{
this.salary = salary;
}
@Override public String toString()
{
return "Employee [id=" + id + ", name=" + name
+ ", department=" + department + ", rating="
+ rating + ", salary=" + salary + "]";
}
}方法二：我们也可以使用GsonBuilder新建一个gson实例。
句法：
Emp json is {"id":"E00101","name":"John","department":"IT","rating":7,"salary":250000.0}
Generated employee from json is Employee [id=E00101, name=John, department=Java, rating=7, salary=250000.0]执行：
示例 1
Java
GsonBuilder gsonBuilder = new GsonBuilder();
Gson gson = gsonBuilder.create();// Java Program where we will be using GsonBuilder object to
// Pretty Print the gson Contents
// Importing I/O classes
import java.io.*;
// Class 1
// Main class
class GFG {
// Main driver method
public static void main(String[] args)
{
// Creating an object of Employee class
Employee emp = new Employee();
// Attributes
emp.setId("F000101");
emp.setName("Dave");
emp.setRating(9);
emp.setDepartment("DB");
emp.setSalary(150000.00);
// Creating a GSON builder
GsonBuilder gsonBuilder = new GsonBuilder();
// Creating a GSON from GSON builder
Gson gson = gsonBuilder.create();
// Creating an employee gson using pretty printing
String empJson = gsonBuilder.setPrettyPrinting()
.create()
.toJson(emp);
// Print and display
System.out.println(
"Emp json in pretty print format:" + empJson);
// Update rating of emp object
emp.setRating(8);
Employee updatedEmp = gson.fromJson(
gson.toJson(emp), Employee.class);
// Print and displaying the updated employee
System.out.println("Updated employee is : "
+ updatedEmp);
}
}
// Class 2
// Helper class
class Employee {
// Attributes
private String id;
private String name;
private String department;
private int rating;
private double salary;
// Member methods of this class
public String getId() { return id; }
public void setId(String id) { this.id = id; }
public String getName() { return name; }
public void setName(String name) { this.name = name; }
public String getDepartment() { return department; }
public void setDepartment(String department)
{
this.department = department;
}
public int getRating() { return rating; }
public void setRating(int rating)
{
this.rating = rating;
}
public double getSalary() { return salary; }
public void setSalary(double salary)
{
this.salary = salary;
}
@Override public String toString()
{
return "Employee [id=" + id + ", name=" + name
+ ", department=" + department + ", rating="
+ rating + ", salary=" + salary + "]";
}
}
If we make any field in Employee class as transient, then Gson library will ignore it during serialization and deserialization and set it to its default value. Let’s understand this with an example.
示例 2
Java
Output:-
Emp json in pretty print format:{
"id": "F000101",
"name": "Dave",
"department": "DB",
"rating": 9,
"salary": 150000.0
}
Updated employee is : Employee [id=F000101, name=Dave, department=DB, rating=8, salary=150000.0]输出：
// Java Program to Make Rating Attribute of Employee class
// as Transient
// Importing required classes
import java.io.*;
// Class 1
// Main class
class GFG {
// Main driver method
public static void main(String[] args)
{
// Creating an object of Gson and user-defined
// Employee class
Gson gson = new Gson();
Employee emp = new Employee();
emp.setName("Jane");
emp.setId("J01012");
emp.setDepartment("Devops");
emp.setSalary(200000.00);
emp.setRating(7);
// Generating json from emp object
String empJson = gson.toJson(emp);
System.out.println("Emp json is " + empJson);
// Changing one of the attributes of emp object
emp.setDepartment("Java");
// Generate emp object from emp json
Employee empGenerated = gson.fromJson(
gson.toJson(emp), Employee.class);
// Print and display the employee generated from
// json
System.out.println(
"Generated employee from json is "
+ empGenerated);
}
}
// Class 2
// Helper class
class Employee {
// Attributes
private String id;
private String name;
private String department;
private transient int rating;
private double salary;
// Member methods of this class
public String getId() { return id; }
public void setId(String id) { this.id = id; }
public String getName() { return name; }
public void setName(String name) { this.name = name; }
public String getDepartment() { return department; }
public void setDepartment(String department)
{
this.department = department;
}
public int getRating() { return rating; }
public void setRating(int rating)
{
this.rating = rating;
}
public double getSalary() { return salary; }
public void setSalary(double salary)
{
this.salary = salary;
}
@Override public String toString()
{
return "Employee [id=" + id + ", name=" + name
+ ", department=" + department + ", rating="
+ rating + ", salary=" + salary + "]";
}
}
输出说明：
当员工对象序列化为 json 时，json字符串不存在 rating 属性，因为它被标记为瞬态。当 json字符串反序列化为员工对象时，作为 int 字段的 rating 将设置为其默认值 0。因此，Gson 库会忽略瞬态字段并根据字段的数据类型将它们设置为默认值。