Jackson中的数据绑定

17 Mar 2025 | 4 分钟阅读

数据绑定概念用于序列化和反序列化数据。它通过使用注解或属性访问器将JSON转换为POJO或反之。

数据绑定API有两种类型

简单数据绑定
完整数据绑定

1. 简单数据绑定

简单数据绑定用于将JSON转换为Map，List，String，Number，Boolean和null对象，或将Map，List，String，Number，Boolean和null对象转换为JSON。

下表定义了JSON和Java类型之间的关系

JSON类型	Java类型
Object	LinkedHashMap<String,Object>
Array	ArrayList<Object>
String	String
完整数字	Integer, Long 或 BigInteger
小数	Double / BigDecimal
True \| False	Boolean
Null	Null

让我们看一个例子来了解简单数据绑定API的工作方式

SimpleDataBinding.java

// import required classes and package
import java.io.File;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;
import com.fasterxml.jackson.core.JsonParseException;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;
// create class SimpleDataBinding to understand the use of Simple Data Binding API
public class SimpleDataBinding {
	
	// main() method start
	@SuppressWarnings("unchecked")
	public static void main(String args[]){
		
		// use try-catch block for conversion Java to JSON type
		try {
			// create instance of the ObjectMapper class
			ObjectMapper mapper = new ObjectMapper();
			
			// create a list of Student
            		Map<String, Student> studentDataMap = new HashMap<String, Student>(); 
            
            		// size of Map
            		int size;
            
            		// create an instance of Scanner class
            		Scanner sc= new Scanner(System.in);
            
            		System.out.println("How many records of Student you have?");
            		size = Integer.parseInt(sc.nextLine());
            
            		for(int i = 0; i < size; i++) {
				
            			Student std = new Student();
				
            			System.out.println("Enter student id: ");
            			String stdId = sc.nextLine();
				std.setStdId(stdId);
				
				System.out.println("Enter course:");
				std.setCourse(sc.nextLine());
				
				System.out.println("Enter first name:");
				std.setFName(sc.nextLine());
				
				System.out.println("Enter last name:");
				std.setLName(sc.nextLine());
				
				System.out.println("Enter full name:");
				std.setPreferredFullName(sc.nextLine());
				
				System.out.println("Enter Enrollment number:");
				std.setEnrol(sc.nextLine());
				
				System.out.println("Enter region:");
				std.setRegion(sc.nextLine());
				
				System.out.println("Enter contact number:");
				std.setPhoneNumber(sc.nextLine());
				
				System.out.println("Enter email address:");
				std.setEmailAddress(sc.nextLine());
				
				studentDataMap.put(stdId, std);
				
			}
            
            		// close Scanner class object
            		sc.close();
            
            		// write Map data into student.json file
            		mapper.writeValue(new File("C:\\Users\\rastogi ji\\Desktop\\student.json"), studentDataMap);
            
            		System.out.println("Your data is written successfully in student.json.\n");
            		System.out.println("Data present in student.json file......");
            	
            		Map<String, Student> data = mapper.readValue(new File("C:\\Users\\rastogi ji\\Desktop\\student.json"), Map.class);
            
            		for (Map.Entry<String, Student> entry : data.entrySet())
                		System.out.println("Key = " + entry.getKey()+", Value = " + entry.getValue());
            
      		}  catch (JsonMappingException exec) {
         		exec.printStackTrace();
      		} catch (JsonParseException exec) {
         		exec.printStackTrace();
      		} catch (IOException exec) {
            		exec.printStackTrace();
      		}
   	}
}

class Student {
	
	// declare variables
	private String stdId;
	private String course;
	private String fName;
	private String lName;
	private String preferredFullName;
	private String enrol;
	private String region;
	private String phoneNumber;
	private String emailAddress;

	public Student(){
	   
	}

	// getter/setters for all variables
	public String getStdId() {
		return stdId;
	}
	public void setStdId(String stdId) {
		this.stdId = stdId;
	}

	public String getCourse() {
		return course;
	}
	public void setCourse(String course) {
		this.course = course;
	}

	public String getFirstName() {
		return fName;
	}
	public void setFName(String fName) {
		this.fName = fName;
	}

	public String getLastName() {
		return lName;
	}
	public void setLName(String lName) {
		this.lName = lName;
	}

	public String getPreferredFullName() {
		return preferredFullName;
	}
	public void setPreferredFullName(String preferredFullName) {
		this.preferredFullName = preferredFullName;
	}

	public String getEnrol() {
		return enrol;
	}
	public void setEnrol(String enrol) {
		this.enrol = enrol;
	}

	public String getRegion() {
		return region;
	}
	public void setRegion(String region) {
		this.region = region;
	}

	public String getPhoneNumber() {
		return phoneNumber;
	}
	public void setPhoneNumber(String phoneNumber) {
		this.phoneNumber = phoneNumber;
	}

	public String getEmailAddress() {
		return emailAddress;
	}
	public void setEmailAddress(String emailAddress) {
		this.emailAddress = emailAddress;
	}

	public String toString(){
		return "Employee [ Student Id: "+stdId+", Course: "+course+ ""
   		+ ", First Name: \"+fName+ \", Last Name: \"+lName+ \""
   		+ ", Name: \"+preferredFullName+ \", Enrol No: \"+enrol+ \""
   		+ ", Region: \"+region+ \", Phone Number: \"+phoneNumber+ \""
   		+ ", Email Address: \"+emailAddress+ \" ]";
	}
}

输出

2. 完整数据绑定

完整数据绑定也用于将JSON转换为任何Java类型，反之亦然。完整数据绑定主要指的是将JSON映射到任何Java类型。

为了将JSON转换为任何Java类型并读取JSON数据，需要使用以下三个步骤

1. 创建一个ObjectMapper类的实例。

3. 将Java对象映射到JSON内容。

让我们看一个例子来了解完整数据绑定如何工作

FullDataBinding.java

package javaTpoint.Jackson;
import java.io.File;
import java.io.IOException;
import java.util.Scanner;
import com.fasterxml.jackson.core.JsonParseException;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;
// create FullDataBinding class to convert Java Object into JSON
public class FullDataBinding {
	
	// main() method start
	public static void main(String args[]){
		
		// create instance of the ObjectSerialization class
		ObjectMapper obj = new ObjectMapper();
		
		Scanner sc1 = new Scanner(System.in);
		
		try {
			
			Product prod = new Product();
			String prodId, prodName, price;
			
			System.out.println("Enter Product Id:");
			prodId = sc1.nextLine();
			prod.setProId(prodId);
			
			System.out.println("Enter Product Name");
			prodName = sc1.nextLine();
			prod.setProName(prodName);
			
			System.out.println("Enter Product Price:");
			price = sc1.nextLine();
			prod.setPrice(price);

			// write data into product.json file
			obj.writeValue(new File("C:\\Users\\rastogi ji\\Desktop\\product.json"), prod);
			
			System.out.println("Your data is written successfully in product.json.\n");
            		System.out.println("Data present in product.json file......");
            
            		Product product = obj.readValue(new File("C:\\Users\\rastogi ji\\Desktop\\product.json"), Product.class);
            		System.out.println(product);

		} catch (JsonParseException e) {
			e.printStackTrace();
		} catch (JsonMappingException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		}
		
		// close scanner class object
		sc1.close();
	}
}
class Product {  
	
	//Creating properties of Product class  
    	private String proId;    
    	private String name;    
    	private String price;  
    
    	//Getter and Setters  
    	public String getProId() {  
        	return proId;  
    	}  
    	public void setProId(String proId) {  
        	this.proId = proId;  
    	}  
    	public String getName() {  
        	return name;  
    	}  
    	public void setProName(String name) {  
        	this.name = name;  
    	}  
    	public String getPrice() {  
        	return price;  
    	}  
    	public void setPrice(String price) {  
        	this.price = price;  
    	}  
    	@Override    
    	public String toString() {    
        	// TODO Auto-generated method stub    
        	return "\"Product [ProductId "+ proId + ", ProductName = " + name + ", ProductPrice = " + price + "]";    
    	}  
}  

输出

下一主题Jackson中的树模型

Jackson中的数据绑定

1. 简单数据绑定

2. 完整数据绑定

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