如何为 Java 应用设置 GSON？
原文:https://www . geesforgeks . org/how-setup-gson-for-Java-application/
GSON 是谷歌的 JSON 解析器。它用于解析 JSON 文件和生成 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 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:
<dependency>
<groupId>com.google.code.gson</groupId>
<artifactId>gson</artifactId>
<version>2.3.1</version>
</dependency>
让我们理解 Gson 如何使用各种 API 进行序列化和反序列化。
考虑一下维护员工信息的 XYZ 公司。因此，我们有员工类，它具有诸如 id、姓名、部门、工资和评级等属性。我们创建一个 Gson 实例，如下所示:
java Gson gson = new Gson();
方法:
- 创建一个具有所有属性的对象，并从中生成一个 GSON
- 使用 GsonBuilder 创建 gson 的新实例
实施:
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
Java 语言(一种计算机语言，尤用于创建网站)
// 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 + "]";
}
}
输出:
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]
方法 2: 我们还可以使用 GsonBuilder 创建 gson 的新实例。
语法:
GsonBuilder gsonBuilder = new GsonBuilder();
Gson gson = gsonBuilder.create();
实施:
例 1
Java 语言(一种计算机语言，尤用于创建网站)
// 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 + "]";
}
}
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]
如果我们将 Employee 类中的任何字段设置为瞬态的，那么 Gson 库将在序列化和反序列化期间忽略它，并将其设置为默认值。让我们用一个例子来理解这一点。
例 2
Java 语言(一种计算机语言，尤用于创建网站)
// 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:
Emp json is {"id":"J01012","name":"Jane","department":"Devops","salary":200000.0}
Generated employee from json is Employee [id=J01012, name=Jane, department=Java, rating=0, salary=200000.0]
输出解释:
当 employee 对象序列化为 json 时，评级属性不会出现在 json 字符串中，因为它被标记为瞬态。当 json 字符串被反序列化为 employee 对象时，作为 int 字段的评级被设置为默认值 0。因此，Gson 库会忽略瞬态字段，并根据字段的数据类型将其设置为默认值。
版权属于：月萌API www.moonapi.com，转载请注明出处
