导入必要的依赖 将JSON处理库加入项目依赖。例如：

    
    
     
        
      
       com.alibaba
      
        
      
       fastjson
      
        
      
       5.2.0
      
    
     
    

定义待转换的实体类 假设定义了一个User类：

public class User {
    private String email;
    private String username;
    private Address address;
    public User(String email, String username, Address address) {
        this.email = email;
        this.username = username;
        this.address = address;
    }
}
public class Address {
    private String street;
    private String city;
    private String country;
    public Address(String street, String city, String country) {
        this.street = street;
        this.city = city;
        this.country = country;
    }
}

使用JSON.toJSONString()方法进行转换 例如：

import com.alibaba.fastjson.JSON;
User user = new User("test@example.com", "testUser", new Address("123 Main St", "New York", "USA"));
String jsonStr = JSON.toJSONString(user);

生成的JSON字符串会类似于：

{"email":"test@example.com","username":"testUser","address":{"street":"123 Main St","city":"New York","country":"USA"}}

验证JSON格式 转换完成后可以使用在线JSON验证工具或代码验证，确保没有语法错误。